CROP RESIDUE MANAGEMENT AND ITS IMPACTS ON SOIL PROPERTIES YUXIN HE. B.E. China Agricultural University, 2007 M.S. Bemidji State University, 2010

Transcription

1 CROP RESIDUE MANAGEMENT AND ITS IMPACTS ON SOIL PROPERTIES by YUXIN HE B.E. Chin Agriculturl University, 2007 M.S. Bemidji Stte University, 2010 AN ABSTRACT OF A DISSERTATION submitted in prtil fulfillment of the requirements for the degree DOCTOR OF PHILOSOPHY Deprtment of Agronomy College of Agriculture KANSAS STATE UNIVERSITY Mnhttn, Knss 2015

2 Abstrct Crop residue removl for livestock feeding nd biofuel production t lrge scles must be evluted to ssess impcts on soil productivity nd properties. Among ll the potentil negtive impcts, wind erosion is mjor concern in the centrl Gret Plins. We conducted n on-frm study from 2011 to 2013 by removing crop residue t five levels (0, 25, 50, 75, nd 100%) to determine the effects of crop residue removl on soil wind erosion prmeters such s dry ggregte size distribution including soil wind erodible frction (EF <0.84 mm ggregtes), geometric men dimeter (GMD) nd geometric stndrd devition (GSD), dry ggregte stbility, nd soil surfce roughness. The sub-model of Wind Erosion Prediction System (WEPS) developed by the USDA-ARS, Single-event Wind Erosion Evlution Progrm (SWEEP) is stnd-lone compnion softwre pckge tht cn be pplied to simulte soil loss nd dust emission from single windstorm event. We pplied mesured dt (i.e. EF, GMD, GSD, nd roughness) to SWEEP for predicting wind velocity tht cn initite wind erosion nd soil loss under ech crop residue removl condition with wind velocity t 13 m s -1. The threshold wind velocity to initite wind erosion generlly decresed with increse in crop residue removl levels, prticulrly for residue removl >75%. The totl mount of soil loss in 3 hours rnged from bout 0.2 to 2.5 kg m -2 nd depends on soil condition nd crop residue cover. On the other hnd, high-yielding crops cn produce bundnt crop residue, which then rises the question tht if frmer wnts to reduce residue, wht could they do without removing it? The ppliction of fertilizer on crop residue to stimulte microbil ctivity nd subsequent decomposition of the residue is often debted. We conducted whet strw decomposition field experiments under different fertilizer rtes nd combintions t three loctions in western Knss following whet hrvest in 2011 nd A double sher box pprtus instrumented with lod cell mesured the sher stress required to cut whet strw nd photomicrogrphy ws used to mesure the cross-sectionl re of whet strw fter shering. Totl C nd N were lso nlyzed. The fertilizer rte nd timing of ppliction during summer 2012 nd Fll 2013 t the Hys site hd impcts on whet strw sher stress t brek point. Across site yers, erlier (fll) fertilizer ppliction generlly resulted in lower remining boveground biomss s compred to spring ppliction. Multivrite nd liner regressions suggested tht N nd C:N rtio prtilly explin the results observed with respect to tretment effects on winter whet residue decomposition.

3 CROP RESIDUE MANAGEMENT AND ITS IMPACTS ON SOIL PROPERTIES by YUXIN HE B.E. Chin Agriculturl University, 2007 M.S. Bemidji Stte University, 2010 A DISSERTATION submitted in prtil fulfillment of the requirements for the degree DOCTOR OF PHILOSOPHY Deprtment of Agronomy College of Agriculture KANSAS STATE UNIVERSITY Mnhttn, Knss 2015 Approved by: Mjor Professor DeAnn Presley

4 Abstrct Crop residue removl for livestock feeding nd biofuel production t lrge scles must be evluted to ssess impcts on soil productivity nd properties. Among ll the potentil negtive impcts, wind erosion is mjor concern in the centrl Gret Plins. We conducted n on-frm study from 2011 to 2013 by removing crop residue t five levels (0, 25, 50, 75, nd 100%) to determine the effects of crop residue removl on soil wind erosion prmeters such s dry ggregte size distribution including soil wind erodible frction (EF <0.84 mm ggregtes), geometric men dimeter (GMD) nd geometric stndrd devition (GSD), dry ggregte stbility, nd soil surfce roughness. The sub-model of Wind Erosion Prediction System (WEPS) developed by the USDA-ARS, Single-event Wind Erosion Evlution Progrm (SWEEP) is stnd-lone compnion softwre pckge tht cn be pplied to simulte soil loss nd dust emission from single windstorm event. We pplied mesured dt (i.e. EF, GMD, GSD, nd roughness) to SWEEP for predicting wind velocity tht cn initite wind erosion nd soil loss under ech crop residue removl condition with wind velocity t 13 m s -1. The threshold wind velocity to initite wind erosion generlly decresed with increse in crop residue removl levels, prticulrly for residue removl >75%. The totl mount of soil loss in 3 hours rnged from bout 0.2 to 2.5 kg m -2 nd depends on soil condition nd crop residue cover. On the other hnd, high-yielding crops cn produce bundnt crop residue, which then rises the question tht if frmer wnted to reduce residue, wht could they do without removing it? The ppliction of fertilizer on crop residue to stimulte microbil ctivity nd subsequent decomposition of the residue is often debted. We conducted whet strw decomposition field experiments under different fertilizer rtes nd combintions t three loctions in western Knss following whet hrvest in 2011 nd A double sher box pprtus instrumented with lod cell mesured the sher stress required to cut whet strw nd photomicrogrphy ws used to mesure the cross-sectionl re of whet strw fter shering. Totl C nd N were lso nlyzed. The fertilizer rte nd timing of ppliction during summer 2012 nd Fll 2013 t the Hys site hd impcts on whet strw sher stress t brek point. Across site yers, erlier (fll) fertilizer ppliction generlly resulted in lower remining boveground biomss s compred to spring ppliction. Multivrite nd liner regressions suggested tht N nd C:N rtio cn explin the results observed with respect to tretment effects on winter whet residue decomposition.

5 Tble of Contents List of Figures... vii List of Tbles... xiii Acknowledgements... xvii Dediction... xviii Chpter 1 - On-frm Assessment of Crop Residue Removl Impcts on Wind Erosion in the Centrl Gret Plins... 1 Abstrct... 1 Introduction... 2 Mterils nd methods... 6 Description of study sites nd tretments... 6 Aggregte size distribution... 7 Aggregte stbility... 9 Surfce rndom roughness... 9 SWEEP modeling Sttisticl nlysis Results Wind erodible frction (EF) Geometric men dimeter (GMD) Geometric stndrd devition Dry ggregte stbility Surfce rndom roughness SWEEP: Wind erosion threshold velocity nd probbility SWEEP: Amount of soil loss t 13 m s -1 wind speed Discussion Conclusions Figures nd Tbles References v

6 Chpter 2 - Effect of Liquid N nd S Fertilizer Solutions on the Mss nd Strength of Winter Whet (Triticum estivum) Residue in No-Till Systems Abstrct Introduction Mterils nd methods Site description nd field experimentl protocols Residue smpling nd nlyses Sttisticl nlysis Results Aboveground biomss Physicl evlution of strw strength Specific Energy (SE) Sher Stress (τs) Chemicl prmeters of whet strw Totl C Totl N C:N Rtio Ash Content Multiple regression: Exmining reltionships between physicl nd chemicl properties.. 92 Simple liner regression between physicl prmeters nd C:N rtio Discussion Conclusions Figures nd tbles References Appendix A - On-frm Assessment of Crop Residue Removl Impcts on Wind Erosion in the Centrl Gret Plins Appendix B - Effect of Liquid N nd S Fertilizer Solutions on the Mss nd Strength of Winter Whet (Triticum estivum) Residue in No-Till Systems Appendix C - SAS Codes vi

7 List of Figures Figure 1.1 Wind erodible frction (EF) (% <0.84 mm) t the L Crosse site. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period Figure 1.2 Wind erodible frction (EF) (% <0.84 mm) t Rush Center. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period Figure 1.3 Wind erodible frction (EF) (% <0.84 mm) t Colby. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period Figure 1.4 Wind erodible frction (EF) (% <0.84 mm) t Norctur. Tretments with different letters indicte significnt differences t the P=0.05 level. Results were seprtely compred mong tretments t ech smpling period Figure 1.5 Wind erodible frction (EF) (% <0.84 mm) t Grden City. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period Figure 1.6 Wind erodible frction (EF) (% <0.84 mm) t Scott City. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period Figure 1.7 Geometric men dimeter (GMD) of dry ggregtes t L Crosse. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period Figure 1.8 Geometric men dimeter (GMD) of dry ggregtes t Rush Center. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period vii

8 Figure 1.9 Geometric men dimeter (GMD) of dry ggregtes t Colby. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period Figure 1.10 Geometric men dimeter (GMD) of dry ggregtes t Norctur. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period Figure 1.11 Geometric men dimeter (GMD) of dry ggregtes t Grden City. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period Figure 1.12 Geometric men dimeter (GMD) of dry ggregtes t Scott City. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period Figure 1.13 Geometric stndrd devition (GSD) of dry ggregtes t L Crosse. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. 40 Figure 1.14 Geometric stndrd devition (GSD) of dry ggregtes t Rush Center. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. 41 Figure 1.15 Geometric stndrd devition (GSD) of dry ggregtes t Colby. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period Figure 1.16 Geometric stndrd devition (GSD) of dry ggregtes t Norctur. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely viii

9 compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period Figure 1.17 Geometric stndrd devition (GSD) of dry ggregtes t Grden City. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. 44 Figure 1.18 Geometric stndrd devition (GSD) of dry ggregtes t Scott City. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. 45 Figure 1.19 Soil dry ggregte stbility (DAS) t L Crosse. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period Figure 1.20 Soil dry ggregte stbility (DAS) t Rush Center. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period Figure 1.21 Soil dry ggregte stbility (DAS) t Colby. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period Figure 1.22 Soil dry ggregte stbility (DAS) t Norctur. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period Figure 1.23 Soil dry ggregte stbility (DAS) t Grden City. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period ix

10 Figure 1.24 Soil dry ggregte stbility (DAS) t Scott City. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period Figure 1.25 Surfce rndom roughness t L Crosse. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t every site t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period Figure 1.26 Surfce rndom roughness t Rush Center. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t every site t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period Figure 1.27 Surfce rndom roughness t Colby. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t every site t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period Figure 1.28 Surfce rndom roughness t Norctur. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t every site t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period Figure 1.29 Surfce rndom roughness t Grden City. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t every site t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period Figure 1.30 Surfce rndom roughness t Scott City. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t every site t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period Figure 1.31 Wind erosion threshold velocity simulted by SWEEP t L Crosse. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period x

11 Figure 1.32 Wind erosion threshold velocity simulted by SWEEP t Rush Center. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. 59 Figure 1.33 Wind erosion threshold velocity simulted by SWEEP t Colby. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period Figure 1.34 Wind erosion threshold velocity simulted by SWEEP t Norctur. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period Figure 1.35 Wind erosion threshold velocity simulted by SWEEP t Grden City. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period Figure 1.36 Wind erosion threshold velocity simulted by SWEEP t Scott City. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period Figure 1.37 Precipittion in 2011, 2012, 2013 nd monthly verge t the L Crosse site Figure 1.38 Precipittion in 2011, 2012, 2013 nd monthly verge t the Rush Center site Figure 1.39 Precipittion in 2011, 2012, 2013 nd monthly verge t the Colby site Figure 1.40 Precipittion in 2011, 2012, 2013 nd monthly verge t the Norctur site Figure 1.41 Precipittion in 2011, 2012, 2013 nd monthly verge t the Grden City site Figure 1.42 Precipittion in 2011, 2012, 2013 nd monthly verge t the Scott City site Figure 2.1 Design of the sher box nd photogrph of the mnufctured sher box Figure 2.2 Testing whet strw physicl strength using sher box ttched with lod cell Instron MN 44 (Instron, Norwood, MA) tht is connected to computer Figure 2.3 Sher force long blde movement recorded by computer with different colors showing different shering stges Figure 2.4 Imge of cross section of whet strw t the breking point under microscope (left) nd being nlyzed by the imge nlysis softwre pckge SigmScn 5 (Systt Softwre Inc.) (right) xi

12 Figure 2.5 Aboveground biomss t Hys site of Summer 2013, Colby site of summer 2012 nd Summer 2013 smpling periods. Brs with the sme letter re not significntly different (p<0.05) Figure 2.6 Specific energy mesured t Hys nd Grden City in summer 2012 nd t Hys in Fll Brs with the sme letter re not significntly different (p<0.05) Figure 2.7 Mesured sher stress t Hys nd Colby during summer 2012 nd Fll 2013 smpling periods. Brs with the sme letter re not significntly different (p<0.05) Figure 2.8 Totl C content mesured t the Hys, Colby, nd Grden City sites in Summer Figure 2.9 Whet strw N contents t Hys in summer 2012, Summer 2013, nd Grden City in summer Dt is not shown for the other site yers Figure 2.10 C:N rtios mesured t Hys nd Grden City in summer 2012 nd Summer Dt is not shown for the other site yers Figure 2.11 Ash contents mesured t Colby nd Grden City in Summer Dt is not shown for the other site yers xii

13 List of Tbles Tble 1.1 Soil informtion, cropping system nd mngement of the six experimentl sites. Soil slope is < 1% t ll sites Tble 1.2 Smpling time t ech reserch site Tble 1.3 Probbility (%) of dys when wind speed reches the wind erosion threshold velocity simulted by SWEEP cross six sites mong four smpling periods. Tretments with different letters indicte significnt differences t the P=0.05 level. Results were seprtely compred mong tretments t every site t ech smpling period Tble 1.4 Amount of soil loss t 13 m s -1 wind speed simulted by SWEEP under 75 nd 100% removl levels t ech site Tble 1.5 Probbility (%) of wind speed 13 m s -1 t the nerest wether sttion from ech study site in ech month Tble 2.1 Fertilizer rtes for ech tretment nd their ppliction time Tble 2.2 Results of nlysis of vrince Tble 2.3 Stepwise multivrite regression prmeters for specific energy nd sher stress s dependent vribles nd totl N, C nd sh content s independent vribles Tble 2.4 Liner regression between physicl prmeters nd C:N rtio Tble 2.5 Anlysis of vrince result of pre-test to determine the number of strw used Tble A.1 Soil EF, GMD nd GSD t L Crosse in fll Tble A.2 Soil EF, GMD nd GSD t Rush Center in fll Tble A.3 Soil EF, GMD nd GSD t Colby in fll Tble A.4 Soil EF, GMD nd GSD t Norctur in fll Tble A.5 Soil EF, GMD nd GSD t Grden City in fll Tble A.6 Soil EF, GMD nd GSD t Scott City in fll Tble A.7 Soil crushing test results nd rndom roughness t L Crosse in fll Tble A.8 Soil crushing test results nd rndom roughness t Rush Center in fll Tble A.9 Soil crushing test results nd rndom roughness t Colby in fll Tble A.10 Soil crushing test results nd rndom roughness t Norctur in fll Tble A.11 Soil crushing test results nd rndom roughness t Grden City in fll Tble A.12 Soil crushing test results nd rndom roughness t Scott City in fll xiii

14 Tble A.13 Soil wind erosion modeling (SWEEP) results t L Crosse in fll Tble A.14 Soil wind erosion modeling (SWEEP) results t Rush Center in fll Tble A.15 Soil wind erosion modeling (SWEEP) results t Colby in fll Tble A.16 Soil wind erosion modeling (SWEEP) results t Norctur in fll Tble A.17 Soil wind erosion modeling (SWEEP) results t Grden City in fll Tble A.18 Soil wind erosion modeling (SWEEP) results t Scott City in fll Tble A.19 Soil EF, GMD nd GSD t L Crosse in spring Tble A.20 Soil EF, GMD nd GSD t Rush Center in spring Tble A.21 Soil EF, GMD nd GSD t Colby in spring Tble A.22 Soil EF, GMD nd GSD t Norctur in spring Tble A.23 Soil EF, GMD nd GSD t Grden City in spring Tble A.24 Soil EF, GMD nd GSD t Scott City in spring Tble A.25 Soil crushing test results nd rndom roughness t L Crosse in spring Tble A.26 Soil crushing test results nd rndom roughness t Rush Center in spring Tble A.27 Soil crushing test results nd rndom roughness t Colby in spring Tble A.28 Soil crushing test results nd rndom roughness t Norctur in spring Tble A.29 Soil crushing test results nd rndom roughness t Grden City in spring Tble A.30 Soil crushing test results nd rndom roughness t Scott City in spring Tble A.31 Soil wind erosion modeling (SWEEP) results t L Crosse in spring Tble A.32 Soil wind erosion modeling (SWEEP) results t Rush Center in spring Tble A.33 Soil wind erosion modeling (SWEEP) results t Colby in spring Tble A.34 Soil wind erosion modeling (SWEEP) results t Norctur in spring Tble A.35 Soil wind erosion modeling (SWEEP) results t Grden City in spring Tble A.36 Soil wind erosion modeling (SWEEP) results t Scott City in spring Tble A.37 Soil EF, GMD nd GSD t L Crosse in fll Tble A.38 Soil EF, GMD nd GSD t Rush Center in fll Tble A.39 Soil EF, GMD nd GSD t Colby in fll Tble A.40 Soil EF, GMD nd GSD t Norctur in fll Tble A.41 Soil EF, GMD nd GSD t Grden City in fll Tble A.42 Soil EF, GMD nd GSD t Scott City in fll Tble A.43 Soil crushing test results nd rndom roughness t L Crosse in fll xiv

15 Tble A.44 Soil crushing test results nd rndom roughness t Rush Center in fll Tble A.45 Soil crushing test results nd rndom roughness t Colby in fll Tble A.46 Soil crushing test results nd rndom roughness t Norctur in fll Tble A.47 Soil crushing test results nd rndom roughness t Grden City in fll Tble A.48 Soil crushing test results nd rndom roughness t Scott City in fll Tble A.49 Soil wind erosion modeling (SWEEP) results t L Crosse in fll Tble A.50 Soil wind erosion modeling (SWEEP) results t Rush Center in fll Tble A.51 Soil wind erosion modeling (SWEEP) results t Colby in fll Tble A.52 Soil wind erosion modeling (SWEEP) results t Norctur in fll Tble A.53 Soil wind erosion modeling (SWEEP) results t Grden City in fll Tble A.54 Soil wind erosion modeling (SWEEP) results t Scott City in fll Tble A.55 Soil EF, GMD nd GSD t L Crosse in spring Tble A.56 Soil EF, GMD nd GSD t Rush Center in spring Tble A.57 Soil EF, GMD nd GSD t Colby in spring Tble A.58 Soil EF, GMD nd GSD t Norctur in spring Tble A.59 Soil EF, GMD nd GSD t Grden City in spring Tble A.60 Soil EF, GMD nd GSD t Scott City in spring Tble A.61 Soil crushing test results nd rndom roughness t L Crosse in spring Tble A.62 Soil crushing test results nd rndom roughness t Rush Center in spring Tble A.63 Soil crushing test results nd rndom roughness t Colby in spring Tble A.64 Soil crushing test results nd rndom roughness t Norctur in spring Tble A.65 Soil crushing test results nd rndom roughness t Grden City in spring Tble A.66 Soil crushing test results nd rndom roughness t Scott City in spring Tble A.67 Soil wind erosion modeling (SWEEP) results t L Crosse in spring Tble A.68 Soil wind erosion modeling (SWEEP) results t Rush Center in spring Tble A.69 Soil wind erosion modeling (SWEEP) results t Colby in spring Tble A.70 Soil wind erosion modeling (SWEEP) results t Norctur in spring Tble A.71 Soil wind erosion modeling (SWEEP) results t Grden City in spring Tble A.72 Soil wind erosion modeling (SWEEP) results t Scott City in spring Tble B.1 Aboveground biomss, totl N content, sh content, totl C content, C:N rtio, SE nd SS t Hys in summer 2012 smpling period xv

16 Tble B.2 Aboveground biomss, totl N content, sh content, totl C content, C:N rtio, SE nd SS t Hys in Summer 2013 smpling period Tble B.3 Aboveground biomss, totl N content, sh content, totl C content, C:N rtio, SE nd SS t Hys in Fll 2013 smpling period Tble B.4 Aboveground biomss, totl N content, sh content, totl C content, C:N rtio, SE nd SS t Colby in summer 2012 smpling period Tble B.5 Aboveground biomss, totl N content, sh content, totl C content, C:N rtio, SE nd SS t Colby in Summer 2013 smpling period Tble B.6 Aboveground biomss, totl N content, sh content, totl C content, C:N rtio, SE nd SS t Colby in Fll 2013 smpling period Tble B.7 Aboveground biomss, totl N content, sh content, totl C content, C:N rtio, SE nd SS t Grden City in summer 2012 smpling period Tble B.8 Aboveground biomss, totl N content, sh content, totl C content, C:N rtio, SE nd SS t Grden City in Summer 2013 smpling period xvi

17 Acknowledgements I would like to express my pprecition nd thnks to those who guided me through my Ph.D. work: Dr. DeAnn Presley for serving s my mjor dvisor nd ptiently teching nd supervising my grdute work. Dr. John Ttrko for serving on my dvisory committee nd teching me bout the fieldwork nd lbortory work. Dr. Gerrd Kluitenberg for serving on my dvisory committee nd providing vluble informtion. Dr. Zifei Liu for serving on my committee nd giving comments on my disserttion. Dr. Humberto Blnco for supervising my first project nd teching me the technique nd procedure of fieldwork. Tom Prosser t KSU Northwest Reserch Frm for mintining the reserch plot nd helping on the fieldwork. Privte producers for providing the study loctions in L Crosse, Rush Center, Norctur, Colby, Grden City, nd Scott City, KS. Michelle Busch, Keith Gustin, nd Srh Ttrko for helping on the fieldwork nd lbortory work. xvii

18 Dediction I would like to dedicte this work to my prents who consistently support nd believe in me. I lso would like to dedicte this work to my uncle Zhigng Pn, who showed nd tught me the importnce of hving good helth nd the power from fmily. xviii

19 Chpter 1 - On-frm Assessment of Crop Residue Removl Impcts on Wind Erosion in the Centrl Gret Plins Abstrct Crop residue removl for livestock nd biofuel production t lrge scles must be evluted to ssess impcts on soil productivity nd ecosystem services. Among ll the potentil impcts, wind erosion is mjor concern in the centrl Gret Plins. We conducted n on-frm study from 2011 to 2013 by removing crop residue t five levels (0, 25, 50, 75, nd 100%) to determine the effects of crop residue removl on soil wind erosion prmeters such s dry ggregte size distribution including soil wind erodible frction (EF <0.84 mm ggregtes), geometric men dimeter (GMD) nd geometric stndrd devition (GSD), dry ggregte stbility, nd soil surfce roughness. Five crop residue removl tretments with four replictions were estblished fter whet hrvest in 9 9 m plots on six frmers no-till fields in western Knss in summer Results consistently showed tht high level of crop residue removl (more thn 75%) incresed the soil wind erodibility s pproximted by severl soil prmeters. Significnt increse in EF, decrese in GMD, nd decrese in surfce roughness were mesured fter complete (100%) residue removl indicting tht complete residue removl is not sustinble in tht it degrdes soil structure. A sub-model of the Wind Erosion Prediction System (WEPS), the Single-event Wind Erosion Evlution Progrm (SWEEP) ws pplied to simulte soil loss nd dust emissions. We pplied mesured dt (i.e. EF, GMD, GSD, nd roughness) to SWEEP for predicting wind velocity tht cn initite wind erosion nd soil loss under ech crop residue removl condition with wind velocity of 13 m s -1 for three hours. The threshold wind velocity to initite wind erosion generlly decresed with increse in crop residue removl levels, 1

20 prticulrly for >75% residue removl. The totl mount of soil loss in 3 hours rnged from bout 0.2 to 2.5 kg m -2 nd depends on soil condition nd crop residue cover. Introduction Lrge scle crop residue removl for bioenergy (i.e., ethnol) production is predicted in the ner future due to the concerns over rising energy costs, dwindling crude oil supplies, incresing energy demnd from developing economies, nd incresing levels of greenhouse gs emissions from trditionl fossil fuel combustion (Blnco-Cnqui nd Ll, 2009; Ll, 2009). Corn (Ze mys L.) stover, sorghum (Sorghum bicolor (L.) Moench) stlks, nd whet (Triticum estivum L.) strw re often considered s primry feedstocks for bioenergy production in the United Sttes becuse of their cknowledged bundnce nd vilbility (Perlck et l., 2005; Srth et l., 2008; Blnco-Cnqui nd Ll, 2009b). The mgnitude of removl levels nd its impcts on soil degrdtion, especilly on soil wind erodibility, hve not been well documented in the centrl Gret Plins. Wind erosion is mjor concern in the centrl Gret Plins (Evers et l., 2013). Dust storms re one of the mjor sources of regionl trnsport of tmospheric prticles. It thretens mny other res throughout the world, such s Beijing, Lnzhou in Chin (Chn nd Yo, 2008), Shelin nd Shrn Afric (Schwnghrt nd Schutt, 2008), Estern Mediterrnen region (Slib et l., 2010), nd Ls Pmps in Argentin (Colzo nd Buschizzo, 2010). Some of the worst dust storms in U.S. history hppened during the 1930 s cross the Gret Plins (Colcicco et l., 1989). 2

21 Crop residue on the ground, prticulrly the stnding residue, cn reduce the ner surfce wind speed, increse soil ggregtion by dding soil orgnic mtter (SOM) (Lyles nd Allison, 1981; Rhoton et l., 2002; Ll, 2004; Wilhelm et l., 2007; Blnco-Cnqui, 2010), nd therefore reduce soil wind erosion. Bilbro nd Fryrer (1988) found tht herbceous plnt mterils could reduce wind erosion nd negtive effects from wind erosion such s dmge to plnts nd decresing crop yield. Effectiveness of crop residue cover on soil wind erosion control depends on the mount nd durtion of soil surfce cover. Evers et l. (2013) stted tht the smll susceptibility of wind erosion on field of wrm seson grss could be ttributed to the constnt soil surfce cover. In cultivted fields, limited or no residue cover nd soil disturbnce by tillge re the mjor fctors tht impct soil wind erosion (Mendez nd Buschizzo, 2010). Compred to conventionl-tillge (CT), no-till (NT) or reduced tillge (RT) my increse surfce soil wter content (Ll, 1982; Mengel et l., 1982), enhnce soil ggregte stbility (Arshd et l., 1999; Wuest et l., 2005; Dm et l., 2005; Hobbs, 2007), nd generlly hve greter bulk density (Hill, 1990; Dm et l., 2005; Krvchenko et l., 2006). It is ssumed, therefore, tht NT nd RT might sustin more residue removl (Vrvel et l, 2008). Previous studies showed tht 50 to 75% of the totl residue production in the Corn Belt region might be vilble for removl (Nelson et l., 2004; Kim nd Dle, 2004; Grhm et l., 2007). However, Blnco-Cnqui nd Ll (2009) observed tht indiscriminte crop residue removl might not be sustinble. Without protection of crop residue on the surfce, 3 ± 0.7 cm crust ws mesured by Blnco-Cnqui et l. (2006) in Ohio. By pplying 2, 4, 8 nd 12 Mg h!! strw, Brid et l. (2006) detected smller soil bulk density nd found the residue cn dissipte the compctive energy by 30%. Blnco-Cnqui nd Ll (2009) found wter retention decresed s the crop residue removl level incresed cross three NT sites in Ohio 3

22 within one yer fter removl. One rinfll simultion completed in the centrl Gret Plins by Kenney et l. (2014) reported significnt crbon loss ssocited with runoff sediments on NT residue removl plots cross three sites in Knss. Crop residue removl my rpidly chnge soil physicl properties such s reduce ggregte stbility (Blnco-Cnqui et l., 2006), increse soil bulk density (Brid et l., 2006), nd decrese SOM content (Wilhelm et l., 2004). Reduction in residue cover cn increse the risk of wind erosion by reducing ggregte stbility nd soil s bility to buffer wind erosive forces (Lyles nd Allison, 1981; Ll, 2009). By removing the most fertile surfce soil, reducing soil wter-holding cpcity, enhncing soil surfce crusting, degrding soil structure nd incresing soil vribility, wind erosion cn reduce soil qulity nd crop productivity (Leys nd McTinsh, 1994). Lrney et l. (1998) mesured whet yield loss nd crbon (C) nd nitrogen (N) enrichment in the depositionl re due to soil wind erosion in Cnd. Also, study of phosphorous (P) trnsport by wind erosion showed possibility of long-term soil productivity reduction (Okin, et l., 2004) Although the function of crop residue on protection of soil from erosion hs been long recognized (Ll, 1982; Mengel et l., 1982; Arshd et l., 1999; Wuest et l., 2005), the quntity of residue tht is required to mintin soil helth nd productivity is not well documented (Wilhelm et l., 2007; Blnco-Cnqui nd Ll, 2009). In semi-rid regions, where precipittion is limited, intensive nd loclized storm events cn cuse soil erosion (Kenny et l., 2014). In the centrl Gret Plins, climtic fluctutions in spring cn result in strong wind events while the freeze/thw process wekens soil ggregtion during erly winter to spring (Ttrko, et l., 2001), which cn excerbte soil wind erosion. 4

23 To estblish the permissible crop residue removl levels for different regions with different wether, soils, nd cropping systems, n ccurte prediction of soil wind erodibility bsed on experimentl dt is needed. Wind erosion models cn be useful to ssess potentil effects of different soil conservtion mngement prctices nd cropping systems (Feng nd Shrrtt, 2009). The Single-event Wind Erosion Evlution Progrm (SWEEP) is the erosion sub-model of the Wind Erosion Prediction System (WEPS) model nd hs grphicl user interfce. The WEPS model is process-bsed model designed to simulte wind erosion soil loss from cultivted griculturl lnds (Wgner, 2013). The SWEEP model cn estimte totl soil loss nd the threshold velocity of wind required to initite wind erosion under different crop residue removl rtes, nd therefore, my help determine the permissible residue removl levels for different soil conditions. The WEPS model cn simulte soil wind erosion on nnul nd periodic (two-week) bsis (Hgen, 1991). Agriculturl mngement prctices, soil types, nd field surfce prmeters re user inputs nd long-term climtic dt re pplied to WEPS to simulte results tht re more ccurte estimtes of soil loss compred to other empiricl models (i.e. the Wind Erosion Eqution WEQ). Buschizzo nd Zobeck (2008) demonstrted tht WEPS hd better results thn WEQ for simulting soil wind erosion in the Argentinen Pmps. Feng nd Shrrtt (2009) tested the SWEEP model by estimting soil loss during high winds on the Columbi Plteu nd concluded tht the model underestimted soil loss by overestimting the threshold friction velocity, but it should be noted tht they studied only smll intensity storms. Ji et l. (2014) pplied the SWEEP model to simulte wind erosion from tiling dm nd estimted the soil loss in different frctions such s totl mteril loss, slttion nd creep loss, suspension loss, nd prticulte mtter less thn 10 microns in dimeter (PM10) loss, etc. Among the soil erodibility prmeters used in WEPS nd SWEEP, ggregte size distribution 5

24 nd stbility, rndom roughness, nd vegettion were found by Hgen et l. (1999) to be mong those tht most influence wind erosion soil loss estimtes. Pired experimentl nd computer modeling dt on soil wind erosion fter crop residue removl re limited, prticulrly for on-frm conditions. To estblish the threshold residue removl levels t which retined crop residues could provide sufficient ecosystem services in western Knss, n ssessment of soil wind erosion is essentil. Therefore, the min objectives of this reserch re 1) to determine effects of corn, whet, nd sorghum residue removl from typicl NT crop rottions on soil wind erodibility prmeters under rinfed (e.g., drylnd) conditions in western Knss, 2) to use the SWEEP model nd mesured soil erodibility prmeters to simulte the wind erosion under different residue tretments nd determine the potentil soil loss, nd 3) to estblish the preliminry threshold levels of residue removl bsed on soil wind erodibility for the representtive soils under NT mngement in this region. Mterils nd methods Description of study sites nd tretments Reserch sites were initited in summer 2011 nd smples were collected during fll 2011, spring 2012, fll 2012 nd spring 2013 cross six on-frm producer-mnged rinfed fields in western Knss. The six on-frm experimentl sites were t (1) L Crosse (38 33 N, W, 627 m bove men se level, i.e., AMSL), (2) Rush Center (38 29 N, W, 599 m AMSL), (3) Colby (39 15 N, W, 963 m AMSL), (4) Norctur (39 47 N, W, 806 m AMSL), (5) Grden City (38 04 N, W, 865 m AMSL), nd (6) Scott City (38 27 N, W, 908 m AMSL). Soil types nd textures t ech loction re listed (Tble 1.1). Texture ws determined using the pipette method (Gee nd Buder, 1986). Soil totl C nd N were lso 6

25 nlyzed by combustion using LEFO TruSpecCN nlyzer (LECO Corp., St. Joseph, MI) (Tble 1.1). Cropping systems were decided by the producers nd therefore, they differed from site to site. All mngement prctices including the crop rottion nd yers in NT production re given in Tble 1.1. Bsed on the stnding height of whet strw left in the field fter hrvest in summer 2011, residue removl heights were clssified into 5 levels (i.e., 0, 25, 50, 75, nd 100% removed). The experimentl design ws rndomized complete block with four replictions. Thus, totl of 20 plots were estblished t ech site. A forge cutter cut whet strw to the height of the ssigned tretment. Due to the NT mngement of ll reserch sites nd historic residue on the ground, for 100% removl plots, weed trimmer nd lef blower were lso used to ccomplish complete removl. In the second nd third reserch yer, crop residue ws cut by forge cutter into different heights ccording to the tretment t ech site fter crop hrvesting. The dimension of the individul plots ws m. A 9.1 m wide lley-wy ws lso estblished between blocks t ech site. Field erodibility prmeters (discussed below) were collected or mesured in the field on the sme dte t ech loction where possible. Aggregte size distribution Soil ggregte size distribution smples were collected in October 2011, Mrch 2012, nd October 2012 from ll six sites. In spring 2013, due to wet soil conditions, soil smpling ws conducted t the Colby, Norctur, Grden City nd Scott City sites in Mrch nd t L Crosse nd Rush Center in erly My. An pproximte 3-kg surfce (0-5 cm) soil smple ws collected from ech plot using flt shovel. Smples were then plced into collection continers for trnsport nd drying. Smples were oven-dried t 60 for three dys. A rotry sieve pprtus (Chepil, 1962 nd Lyles et l., 1970) ws used to seprte ggregtes into size clsses tht were 7

26 weighed to determine the mss from ech sieve size frction. Sieve size openings were <0.42, , , , , , nd >44.45 mm in dimeter. To evlute soil erodibility, soil wind erodible frction (EF), geometric men dimeter (GMD), nd geometric stndrd devition (GSD) were clculted from the mss frction of the different sizes. EF is computed s the percentge of ggregtes less thn 0.84 mm in dimeter (Chepil, 1952). The eqution to clculte EF is EF = M! M! 100 where EF is the erodible frction (%), M! is the weight (g) of ggregtes with dimeter less thn 0.84 mm, nd M! is the totl weight (g) of totl smple. GMD describes the ggregte size in dimeter t which 50% of soil smple in mss is lrger thn nd 50% of it is smller thn nd GSD describes the distribution pttern of soil ggregte size. GMD nd GSD were clculted from Wgner nd Ding (1994) method s below. GMD = exp m! ln d!!!!!!! GSD = exp [ m! ln d! ln GMD! ]!.!!!! where m! represents the mss of soil ggregtes in certin size collection pn, nd d! represents the men dimeter of ech of the seven size frctions. 8

27 Aggregte stbility Soil ggregtes were collected from ech plot t the sme time with s soil ggregte size distribution smples. Aggregtes were collected using flt shovel from the top 5 cm soil nd pssed through 12.7 mm dimeter sieve in the field. Aggregte smples were then ir dried in greenhouse ( 25 ) for week. A Soil Aggregte Crushing Energy Meter (SACEM) pprtus ws used to mesure nd record the energy required to crush individul ggregtes (Boyd et l., 1983). The SACEM is comprised of two prllel pltes supported by lod cell, which is connected to computer to mesure force nd energy s the pltes crush the ggregte smple. For the test, subsmple of 30 ggregtes from the dried field ggregtes hving mss 5 grms ech were picked nd reformed by minor finger mnipultion to remove edges nd form into pproximte sphericl shpe. The result of SACEM is dry ggregte stbility presented s the nturl log of the crushing energy per unit mss (ln (J kg!! )) s described by Hgen et l., (1992). Surfce rndom roughness A micro-relief pin meter ws pplied to mesure the rndom surfce roughness of ech plot long the ridge tops (Wgner nd Yu, 1991; Skidmore et l., 1994). Rndom roughness mesurements were conducted for ll site yers except for L Crosse nd Rush Center in spring 2012 due to the presence of whet crop growing in those fields. A pin meter consists of 101 pins (1 cm prt, 50 cm in length nd 6 mm in dimeter) mounted on metl guide in front of white bckbord. The guide nd pins re lowered to the soil surfce so tht the pin tops replicte the soil surfce elevtions. Any residues present were crefully removed so tht the pins touched the ctul soil surfce. A digitl imge of the tops of the pins ws cptured in ech plot by digitl cmer. Sigm Scn Pro 5 (SPSS Science, 1998) softwre ws then used to nlyze the digitl 9

28 photos to obtin soil elevtion of ech pin. Roughness ws clculted s the stndrd devition of the pin heights fter correction for slope (Allmrs et l., 1966; Wgner nd Yu, 1991). SWEEP modeling An m squre field with no wind brriers ws simulted in SWEEP to estimte soil wind erosion under different residue removl levels t ll six sites bsed on the mesured prmeters (i.e., GMD, GSD, ggregte stbility, roughness, residue height, nd residue chrcteristics). Biomss informtion ws input into the SWEEP model for ech tretment t different sites. According to the distnce between the ground nd the forge cutter blde for ech tretment, 0.0, 0.075, 0.15, 0.225, nd 0.3 m were pplied s whet strw residue verge heights corresponding to 100, 75, 50, 25, nd 0% residue removl levels t ech site in the model. Likewise, 0.0, 0.15, 0.3, 0.45, nd 0.6 m were used s sorghum stlk residue verge heights nd 0.0, 0.125, 0.25, 0.375, nd 0.5 m were for corn stlk heights. Residue stem re index ws clculted by SWEEP from stem dimeter, stem height, nd stem popultion. In this study, we used 3, 30, nd 60 mm s whet, sorghum, nd corn residue dimeters. According to the WEPS defult dtbse, stem popultions for whet strw, sorghum stubble, nd corn stlks were 500.0, 24.71, 7.41 plnt m -2, respectively nd these vlues were used in our simultions. Residue lef re index ws ssumed to be zero under ll tretments t ll sites becuse the lef prts of plnt were removed during hrvest. Residue flt cover prmeters were estimted by compring field plots with photogrphs of known cover. Cover vlues of 0.0, 0.3, 0.5, 0.6, nd 0.7 m 2 m -2 corresponded to 100, 75, 50, 25, nd 0% residue removl levels. Since crops hd been hrvested before smpling, growing crop prmeters were ll ssumed to be zero in SWEEP. SWEEP hs the cpbility to downlod the USDA-Nturl Resource Conservtion Service Soil Dt Mrt file to import bsic soil informtion bsed on soil series t ech site. Then field-mesured prmeters 10

29 (i.e., EF, GMD, GSD, nd rndom roughness) were replced for dtbse-generted vlues. To estimte ir density t smpling time, elevtion nd dily verge temperture for the smpling month were pplied. To simulte the soil wind erosion under extreme conditions, mss of soil loss (kg m -2 h -1 ) t 13 m s!! ( 29 miles hr!! ) wind speed for 3-hour event ws determined. In ddition, threshold wind velocity (i.e., the wind velocity t which soil erosion initites), nd percent of dys tht greter thn threshold wind velocities cn be expected in the smpling month were determined by the SWEEP model using historicl wind prmeters t ech site. Sttisticl nlysis All dt were sttisticlly nlyzed using nlysis of vrince (Mixed procedure) in SAS 9.3 (SAS Institute, 2011). Lest squre mens t the 0.05 significnce level ws pplied to test the differences mong tretments (SAS Institute, 2011). Results Wind erodible frction (EF) Crop residue removl significntly ffected soil EF t ll six sites nd for ll smpling dtes (Fig. 1.1 Fig. 1.6). However, the mgnitude of removl effects vried with site. Four months fter reserch ws initited (fll 2011), residue removl hd no significnt impcts on EF t three out of six sites, while t Colby, Rush Center, nd Scott City sites there were significnt differences in EF mong tretments. At Colby, EF ws 26.58% t 25% removl, which ws pproximtely 15% less thn EF for the 75% removl plot. At Rush Center, the 100% removl plot hd significntly greter EF compred to the 0 nd 50% removl tretments. A similr pttern ws lso mesured t the Scott City site. The EF t 100% removl tretment ws 55.51%, which ws pproximtely 54 nd 55% greter thn mesured vlue t 25 nd 0% removl plots, respectively. 11

30 In spring 2012, nine months fter the plot estblishment, significntly greter EFs with incresed residue removl levels were mesured t ll sites. At L Crosse, residue removl did not hve impcts on soil EF. However, EF ws 54.68% under 100% removl t Rush Center, which ws pproximtely twice s much s the 0% removl plot. At Colby, EFs for the greter thn 50% residue removl plots (i.e. 75 nd 100% residue removl) were significntly greter compred to other tretments. The lowest vlue mesured ws for the 25% removl plots, which ws 37.86%, nd ws hlf s mny t 100% removl plot, which ws the highest EF found t this site. At Norctur, EF for complete residue removl (53.03%) ws significntly greter thn the other tretments, where EFs rnged from to 27.36% mong 0 to 75% removl plots. Significntly less EF ws mesured for the 0% removl tretment compred to 100% removl tretment t the Grden City site. The EF ws 37.42% t 0% removl plot. In contrst, EF pproximtely doubled (68.47%) with 100% removl. Similr to the Norctur site, 100% removl tretment hd significntly greter EF thn the other tretments t the Scott City site. The EF ws 64.93% for the 100% removl plot, which ws pproximtely twice s much s the other tretments, where the EFs rnged from to 38.81%. In fll 2012, residue removl hd significnt impcts on EF t four out of six sites. At Colby, nd Grden City sites, there were no significnt effects of residue removl on EF. At L Crosse, 100% removl plot hd significntly greter EF t 44.28%, compred to other tretments where EFs rnged from bout 24 to 28%. At Rush Center, EF for the complete residue removl tretment ws significntly greter thn for no residue removl. The mesured EF ws 55.50% for 100% removl tretment nd ws more thn twice greter thn 0% removl plot. At Norctur, the complete cover tretment hd significntly less EF compred to 25 nd 100% removl tretments. The highest EF mesured ws t 100% residue removl, which ws twice s much s 12

31 0% removl t 27.79%, while the 25% removl tretment hd 36.11% EF. At Scott City, EF for 100% removl ws significntly greter thn the 25 nd 0% removl tretments. In spring 2013, significnt impcts of residue removl on EF were found t ll six sites. At L Crosse, EF for complete residue removl ws significntly greter thn for ll other tretments. The EFs mesured were 44.28% t 100% removl tretment, which ws more thn twice s much s other tretments, where the EFs rnged bout from 17% to 22%. At Rush Center, 0, 25, nd 50% removl tretments hd less EF compred to 75 nd 100% removl. At Colby, 50% removl hd significntly greter EF thn the complete covered plot. At Norctur, highest EF ws mesured for the complete removl tretment. In contrst, 25 nd 50% residue removl tretments hd significntly less EFs, which were pproximtely 25%. EF t Grden City under complete residue cover ws significntly less thn the 50, 75, nd 100% residue removl levels. Menwhile, the highest EF ws gin observed for 100% removl, which ws 65.40%. At Scott City, the complete residue removl tretment hd the highest EF nd the lowest EF mesured ws t 0% removl plot. Geometric men dimeter (GMD) Crop residue removl ffected soil GMD t ll six sites over time (Fig. 1.7 Fig. 1.12). In fll 2011, immedite impcts of crop residue removl on GMD were found t four out of six sites (i.e., four months fter study ws initited). They re Rush Center, Colby, Norctur, nd Scott City. At the Rush Center site, the smllest GMD (1.15 mm) ws mesured for 100% removl, versus 4.88 mm for the 0% removl tretment. At Colby, significntly different GMDs were found between 75% nd 25% removl tretments. The lrgest GMD (2.61 mm) ws mesured under 25% removl tretment, which ws more thn twice the GMD thn the 75% removl plot. At Norctur, GMDs under the 0, 75, nd 100% tretments were significntly less thn the 50% 13

32 removl rte t mm. The smllest vlue t this site ws mesured t 100% removl tretment. A similr pttern ws observed t Scott City, where 50% removl hd highest GMD while the lowest vlue ws mesured t the complete removl. In spring 2012, significnt impcts on GMD due to crop residue removl were observed t ll six sites. At L Crosse, the smllest GMD (1.47 mm) ws mesured for 100% removl, which ws less thn hlf of wht ws observed for the 50% removl level. At Rush Center, compred to 0 nd 25% removl, the 100% removl plot hd significntly smller GMD, which ws 0.62 mm. At the Colby site, the smllest GMD ws mesured t 100% removl, which ws significntly smller thn 0% removl plot. Menwhile, the GMD t 75% removl ws lso significntly smller thn the complete removl. Similrly, the smllest GMD (0.68 mm) ws mesured for 100% removl t the Norctur site, which ws significntly smller thn 0, 25, nd 50% removl plots. At Grden City, significntly different GMDs were mesured between 0 nd 100% removl plots. The lrgest vlue (1.27 mm) ws mesured t 0% removl plot, which ws five times the GMD mesured with complete removl. At the Scott City site, the highest GMD (3.82 mm) ws mesured t 50% removl plot, which is significntly lrger thn vlues under 0, nd 100% removl. In fll 2012, significnt impcts of crop residue removl on GMD were mesured t three out of six sites. At the L Crosse site, the smllest vlue (1.09 mm) ws mesured under 100% removl, which ws significntly less thn 0% removl. At Rush Center, GMD mesured t 100% removl plot ws significntly smller thn other tretments. At the Norctur site, the highest GMD ws 2.75 mm under 0% removl, nd GMDs t 25 nd 100% were significntly smller. 14

33 In spring 2013, significnt results were mesured t four out of six sites. At L Crosse, the lowest vlue ws observed for the complete removl tretment, which ws 1.03 mm nd ws significntly smller thn t 50 nd 75% removl levels. At Rush Center, highest GMD ws mesured t 25% removl while the significntly smller vlues were mesured t 0, 75, nd 100% removl. At Grden City, the smllest GMD (0.33 mm) ws mesured t 100% removl plots. Comprtively, the highest vlue ws mesured t 0% removl tht ws twice s lrge s the complete removl tretment. At the Scott City site, GMD under the 100% residue removl tretment ws significntly smller thn the 0 nd 75% removl tretments. Geometric stndrd devition As shown in Fig to Fig. 1.18, four months fter the study ws initited, significnt differences due to crop residue removl were mesured t the L Crosse nd Colby sites. At L Crosse, the smllest GSD (13.37 mm) ws mesured t 25% removl plot while the vlues mesured t 0, 75, nd 100% removl tretments were significntly greter. A similr pttern ws mesured t the Colby site. The smllest vlue ws mesured under 25% removl. Significntly greter GSDs were mesured t 0, 75, nd 100% removl plots. In spring 2012, significnt impcts of crop residue removl on soil GSD were found t three out of six sites (Rush Center, Colby, nd Grden City). At Rush Center, the GSD mesured t 0% removl ws the smllest mong ll tretments, which ws 8.21 mm. The GSDs mesured t 25 nd 100% removl plots were significntly greter (40 nd 35% lrger, respectively) reltive to 0% removl plot. At Colby, the GSDs from 0, 25, nd 50% removl rtes were significntly greter thn from 75 nd 100% removl. At the Grden City site, the highest GSD ws mesured t 25% removl, which ws mm. Vlues from the 75 nd 100% removl tretments were 20 nd 26% less, respectively. 15

34 In fll 2012, significnt differences were mesured t the Colby nd Scott City sites only. Similrly, the highest vlues were both from 25% removl tretment t these sites. The smllest GSD ws mesured t 75% removl t Colby nd t 0% removl t Scott City, respectively. In spring 2013, impcts of residue removl on GSD were mesured t L Crosse, Rush Center, nd Colby. At the L Crosse site, the gretest GSD (17.36 mm) ws from 100% removl, which ws significntly more thn 0, 25, nd 50% removl tretments (31, 40 nd 49% greter, respectively). Similrly, the gretest GSD (15.77 mm) t Rush Center ws from the complete removl plots s well. GSD ws pproximte 64% greter thn the result from 50% removl tretment, which ws the smllest result mesured t this site. At Colby, significntly different results were mesured between 25 nd 50% removl tretments. GSD from 25% removl plot ws 24% greter thn the results from 50% removl tretment. Dry ggregte stbility Residue removl impcts on dry ggregte stbility (DAS) were significnt t some sites nd some smpling periods. However, the reltionship between ggregte stbility nd residue removl levels gretly vried from site to site nd time to time (Fig Fig. 1.24). To pply stbility to SWEEP modeling, nturl log formt of energy per unit mss is reported (ln(j kg -1 )). In fll 2011, significnt impct of crop residue removl on DAS ws only mesure t the Colby site. DAS mesured t both 0 nd 100% removl tretments were significntly greter thn the 50% removl tretment in fll Two out of six sites mesured significnt chnges in DAS in spring 2012 smpling period. At L Crosse, complete residue removl ws less stble s compred to the 0 nd 50% removl 16

35 tretments. At Scott City, the smllest stbility vlue in spring 2012 ws mesured t complete residue removl plot, which ws significntly less thn the other tretments. In fll 2012, significnt differences in DAS due to crop residue removl were mesured t L Crosse, Rush Center, nd Colby. The 100% removl tretment hd the lowest stbility, which is significntly less thn other tretments t the L Crosse site. At Rush Center, soil ggregtes from the complete removl tretment were significntly less stble compred to the soil ggregtes from 0, 25, nd 50% removl plots. However, t Colby, the complete residue removl tretment hd the most stble soil ggregtes, which hd significntly greter DAS thn other tretments. Four out of six sites showed significnt impcts of residue removl on DAS during the spring 2013 smpling period. At Rush Center, DAS t 50% removl ws significntly greter thn 75 nd 100% removl plots. DAS vlues t 0, 25, nd 50% removl plots were significntly less thn for the 100% removl tretment t the Colby site. At Norctur, the lrgest DAS ws mesured t 25% residue removl plot, which ws significntly greter thn complete removl. At the Scott City site, the DAS mesured under 75 nd 100% removl tretments ws significntly lrger thn for the 50% removl plot. Surfce rndom roughness Impcts of crop residue removl on soil surfce rndom roughness were significnt t some sites. However, the dt gretly vry between sesons nd sites (Fig Fig. 1.30). Due to the growing whet t L Crosse nd Rush Center sites, we did not mesure surfce roughness for this smpling period t those two sites in spring

36 At L Crosse, roughness vlues in fll 2011, fll 2012, nd spring 2013 did not show ny differences mong ll tretments in ech smpling period. However, the verge vlue in fll 2012 ws greter thn other times. The roughness vlues in fll 2011 nd spring 2013 rnged from bout 4 mm to 6 mm nd from bout 4.5 mm to 7.8 mm, respectively. In fll 2012, the vlues rnged from bout 8.2 mm to 9.5 mm. At Rush Center, roughness in fll 2011 nd spring 2013 did not differ mong ll tretments. In fll 2012, vlues from 0, 25, nd 50% removl tretments were significntly greter thn from the complete removl plot. Roughness vlues in spring 2013 rnged from bout 4.5 mm to 6.5 mm nd were smll compred to the other two smpling periods. Impcts of residue removl on surfce roughness were considerble in the first two smpling periods t Colby. Four months fter reserch strted, 75 nd 100% residue removl tretments hd significntly less roughness thn 0, 25, nd 50% removl plots. The flttest roughness mesured ws complete removl t 1.75 mm. The gretest roughness ws from the 0% removl tretment, which ws pproximtely six times s rough s the complete removl tretment. Similrly, in spring 2012, significntly less roughness ws mesured t 75 nd 100% removl compred to 0, 25, nd 50% removl tretments. Additionlly, compred to complete residue cover, 25% removl hd significntly lesser roughness. In fll 2012 nd spring 2013, the surfce roughness vlues were sttisticlly the sme mong ll tretments. Although not significnt, Spring 2013 did show trend where 100% removl hd less roughness thn 0% removl. The chnge of surfce roughness due to crop residue removl t Norctur did not show cler pttern. In fll 2011, the gretest roughness ws mesure t 50% removl, which ws 8.3 mm. Similr to fll 2011, 50% removl hd gretest surfce roughness in spring In fll 18

37 2012, the gretest roughness vlue ws 8.5 mm fort 75% removl tretment, nd ws significntly greter thn both 50 nd 100% removl. In spring 2013, roughness vlues t ll tretments were sttisticlly similr. At Grden City, in fll 2011, 0 nd 25% removl plots hd significntly greter roughness vlues thn complete residue removl. A similr pttern ws lso observed in spring In fll 2012, there ws no sttisticl difference between tretments on roughness vlues. In spring 2013, the gretest roughness ws mesured t 50% removl, which ws significntly greter thn complete removl. The effects of residue removl on surfce roughness hd cler pttern t Scott City, where complete residue removl tretment hd the smllest roughness vlues, in other words, hd the smoothest surfce. In fll 2011, vlues from 100% removl ws significntly less thn vlues from 0, 25, nd 50% removl. In spring 2012, fll 2012, nd spring 2013, the complete residue removl tretment ws the smoothest. SWEEP: Wind erosion threshold velocity nd probbility At ech site, the SWEEP simulted threshold velocity (V! ) required to initite wind erosion decresed with increse in residue removl levels. Smllest V! (rnged from 6 to 10 m s -1 ) ws lwys estimted t 100% removl plots, wheres the lrgest vlues (rnged from 17 to 21 m s -1 ) were estimted t 0% removl tretment t ech site (Fig Fig. 1.36). Threshold velocities under the 100% removl tretments t ech site were ll significntly less thn 75% removl plots during every smpling period. A similr pttern ws found between 75 nd 50% removl tretments. The only exception ws t Grden City during the first smpling period (4 months 19

38 fter study initited). No significnt difference of threshold velocities ws mesured between these two tretments t this site. The V! under 50 nd 25% residue removl tretments hd no significnt difference t L Crosse, Rush Center, Colby, nd Norctur t ll 4 smpling periods. At Grden City, wind erosion V! under 50% removl plots ws significntly less thn 25% removl tretments in the fll 2011 nd spring The estimted V! for the 50% removl tretments were nd m s -1 in the fll 2011 nd spring 2012, respectively, nd velocities under the 25% removl tretments were 18.5 nd 17 m s -1 for fll 2011 nd spring For most of the smpling periods, the difference of V! between 25 nd 0% removl tretments were not significnt t ll six sites. However, t L Crosse, Rush Center, nd Grden City, significnt less V! t 25% residue removl plots ws mesured in spring Also, in fll 2012, V! t 25% residue removl tretment ws estimted significntly less thn 0% residue removl plot t Scott City. The probbility of dys when wind speed reches the V! is reported in Tble 1.3. At ll six sites, the probbility of hving dys with wind speed greter thn V! t 100% residue removl plots ws significntly greter thn other tretments. The probbility lso vries from site to site nd time to time. Smller probbility vlues were estimted t L Crosse, which for complete residue removl plots rnges from 9.6% to 17.7%. The lrgest vlues were found t Grden City nd Scott City, which vry from bout 14.4% to 50.9% for 100% residue removl tretment. For 75% residue removl tretment, the gretest probbility of dys with wind speed greter thn V! ws significntly less reltive to 100% removl. The lrgest probbilities were mesured t Colby nd Grden City, which were pproximtely 5%. At other sites, the probbility ws 20

39 usully less thn 3%. The probbility declined to less thn 1% when more thn 50% residue ws left on the soil surfce t ll 6 sites for most of the smpling periods. SWEEP: Amount of soil loss t 13 m s -1 wind speed When wind erosion ws simulted using field mesured prmeters nd 13 m s -1 velocity, the soil wind erosion is only initited when t lest 75% residue is removed from the field t ll six sites (Tble 1.4). For ll plots, 50% residue retined hd no soil loss predicted t wind velocity of 13 m s -1. For 100% residue removl plots, wind erosion hppens t ll sites with wind speed of 13 m s -1. At L Crosse, totl soil loss incresed from 0.97 kg m -2 in the fll 2011 to 1.69 kg m -2 in spring A similr increse from fll 2011 to spring 2012 ws found t ll sites (Tble 1.4). From fll 2012 to spring 2013, four sites (i.e. L Crosse, Norctur, Grden City, nd Scott City) hd simulted increse in soil loss nd nother two sites (i.e. Rush Center nd Colby) hd decrese. Discussion Dt on soil wind erosion prmeters showed tht crop residue removl could result in severe wind erosion t some sites. The mgnitude nd frequency of the impcts of residue removl on soil erodibility vried likely due to the differences in soil types, cropping systems, historic mngements, nd locl climtic fctors. For wind erosion control purposes, keeping minimum crop residue of more thn 25% on the ground fter hrvest could reduce the soil s susceptibility to wind erosion in the Gret Plins. Soil texture cn be used to prtilly explin the mgnitude of the effects of crop residue removl on soil erodibility. Mild chnges from fll 2011 to spring 2012 in EF were observed t Rush Center nd Scott City compred to other sites, prticulrly for the complete removl 21

40 tretment (Fig. 1.1 Fig. 1.6). Although ll six sites hve silt lom, the soils t L Crosse nd the Scott City hve greter (18%) cly content (Tble 1.1). Cly enriched soil usully hs better wind erosion resistnt bility due to the stronger cohesive forces between soil prticles nd better bonding conditions from humus resulting in stronger ggregtion. Zobeck nd Bilbro (2001) found tht eroded soil surfce tend to hve greter cly content. Indiscriminte crop residue removl could expose soils to wethering tht could degrde soil structure nd cuse wind erosion issue in western Knss. This is prticulrly true when considering the EF vlues cross the six reserch sites. High EF indictes incresed wind erodibility under certin conditions. At lmost ll sites, complete residue removl significntly incresed EF. According to Chepil (1945), initition of soil movement by wind begins with slttion of soil prticles. Without the protection of crop residue, bre soil with higher EF could be exposed to wind; when the V! is reched, wind erosion cn occur. EF vlues incresed t five sites from fll 2011 to spring 2012 (Fig. 1.1 Fig. 1.6), prticulrly for high removl rte plots (i.e. 75 nd 100% removl). This increment could be ttributed to the locl wether conditions (Li et l., 2004). The most likely period of the yer to hve wind erosion in western Knss is lte winter to erly spring due to, mong other fctors, the freeze/thw effects on soil ggregtes (Lyton et l., 1993). In this period, the plnt height is not high enough to slow the wind t the soil surfce. Also during winter, due cold tempertures, soil pore wter is often frozen which hs lrger volume thn liquid wter. The freezing process will expnd the pore size between soil ggregtes, which cn cuse soil ggregtes to brek up nd weken stbility nd therefore, increse the susceptibility of soil wind erosion (Bullock et l., 2001; Li et l., 2004; Wng et l., 2014). In this study, in erly spring 2012, winter whet ws growing t L Crosse nd Rush Center. At this time, winter whet is usully short nd sprse in 22

41 the field. Due to the low humidity during the winter in US Gret Plins, sublimtion of frozen wter cn be expected t the soil surfce leving empty soil pores nd wekened ggregtes. Ttrko et l. (2001) found tht the freeze/dry process cused less stble soil ggregtes regrdless the soil wter content nd stbility decrese s soil wter increses. In the erly spring, wrmer tempertures will dditionlly thw deeper soil. A similr increse of EF fter winter ws not observed in smples from fll 2012 to spring 2013, which is likely due to mngement chnges necessitted by mjor drought. In spring 2012, sorghum ws plnted t L Crosse nd Scott City sites nd corn ws plnted t Colby nd Norctur sites. Due to severe drought in summer nd fll 2012 for bout two thirds of Knss, prticulrly in western prt (HPRCC, 2012), crop yields were extremely low nd producers t L Crosse, Colby, Norctur, nd Scott City decided not to hrvest. Therefore, the residue height remining in the field t these sites for tht yer ws greter thn the previous yers. Menwhile, for wind erosion control purposes, the producer t Rush Center imported dditionl whet strw into field fter hrvest in My 2012, which resulted in lrge mounts of in situ crop residue. Although we hrvested forge to different heights ccordingly fter the producers bndoned the crops in fll 2012, greter boveground biomss ws observed, which provided extr protection on the surfce soil during winter, hence the probble cuse why EF did not increse over the winter of Effects of residue removl on soil ggregte stbility re complicted by other fctors such s soil texture, wter, temperture, snow cover, nd mngement history. Results from mny sites showed tht differences in ggregte stbility mong tretments were not significnt. There ws no significnt difference found t Grden City t ll four smpling periods. Grden City hs the shortest NT mngement history mong ll study sites before reserch initited, which ws 5 23

42 yers. Strong soil structure might not develop in such short period compred to other sites. Six et l. (1999) found tht tillge could grdully reduce soil ggregte stbility. Menwhile, Grden City hs gretest cly content mong ll sites (Tble 1.1), which my offset the effects of crop residue removl on DAS. At the Norctur site, significnt differences were only mesured t the lst smpling period. One reson is tht Norctur hs the longest NT history, which ws 20 yers nd ggregtion my be more developed t this site. Rhoton (2000) stted tht NT prctices could enhnce soil erodibility-relted properties. Menwhile, two out of four smpling periods showed significnt impcts of crop residue removl on soil ggregte stbility t L Crosse, Rush Center, nd Scott City. Also, significnt results were mesured three times t the Colby site. It is hypothesized tht stbility would decrese with increse in residue removl levels. This pttern ws only found in the spring 2012 t Colby nd Scott City, nd fll 2012 t Rush Center. However, the opposite pttern in which ggregte stbility incresed with increse in residue removl ws found in fll 2012 t Colby, nd spring 2013 t Colby nd Scott City. A possible reson for this phenomenon could be the soil surfce seling nd crusting ws visully observed for the lower residue tretment plots. Precipittion from My to September my lso reconsolidte nd strengthen ggregtes. Without the protection of crop residue, rindrop energy is directly trnsferred to the soil prticles. The relese, movement, nd orienttion of fine prticles cn clog the pores ner the soil surfce nd eventully cuse soil surfce seling. During the drying process, soil sel cn develop into high physicl strength crust (Blnco-Cnqui et l., 2006). Surfce crusts cn temporrily increse soil strength nd decrese wter infiltrtion rte (Benymini nd Unger, 1984). A complete nd continuous crop residue cover on the ground could eliminte the formtion of surfce sels (Run et l., 2001). 24

43 Rough soil surfces cn reduce the ner surfce wind velocity (Bielders et l., 2000) by bsorbing wind energy nd cn trp soil prticles, reducing wind erosion. For five out of six sites, soil surfce roughness decresed with increse in residue removl levels. Precipittion cn fltten the soil surfce nd reduce ggregtion s observed by Ttrko et l. (2001). This ws likely the reson for reduced rndom roughness under the complete removl tretment where surfce soil ws exposed to freezing tempertures nd precipittion. The SWEEP model predicted the V!, the probbility of n erosion event, nd totl soil loss for three-hour wind t 13 m s -1 under every tretment t ech site. Reduced V! with complete residue removl indictes the importnce of protection of crop residue on reducing soil wind erodibility. This decrese ws consistently simulted t every site suggesting other fctors (i.e. mngement history, cropping system, nd locl wether condition, etc.) do not ffect soil wind erodibility s much s the presence of crop residues, prticulrly in the short term (1-2 yers of this study). The results indicte tht ggressive residue removl (>75%) cn increse the possibility of soil wind erosion. Tht is especilly essentil in the semi-rid re, where wind erosion hs lwys been thret due to high winds nd periodic drought. The probbility of dys when wind erosion cn be initited, which ws bsed on historic wind sttistics in SWEEP, lso increses significntly with excessive crop residue removl (>75%) (Tble 1.3), prticulrly in the erly spring when there is high probbility for windy wether. At ll sites, the probbilities of dys with wind speed tht cn initite soil erosion t less thn 75% residue removl plots re extremely smll. Therefore, complete residue removl my not be sustinble, but prtil removl up to s much s 75% my be possible depending on timing of removl (e.g., just prior to plnting) nd locl conditions (e.g., high biomss present). 25

44 Soil loss for three-hour wind velocity of 13 m s -1 ws simulted for 100% residue removl tretment t ll six sites over four smpling periods. Such wind speeds re not uncommon in the study re (Tble 1.5). In ddition, over hlf of the erosion losses t 100% removl were in excess of the tolerble limit of 1.12 kg m -2 (5 T c -1 ) for these soils (Tble 1.4), nd ll but one (Rush Center, Fll 2011) were in excess of 0.45 kg m -2 (2 T c -1 ). However, none of the showed hd soil wind erosion t wind speed of 13 m s -1 when more thn 50% of residue remined in the field. At Colby nd Grden City, results show tht wind erosion could even hppen for the soil conditions mesured t 75% residue removl, which re significntly different compred to 0, 25, nd 50% removl tretments. NT systems often hve better soil ggregtion t the soil surfce thn other tillge prctices (Devine et l., 2014). Therefore, greter soil wind erodibility t Grden City my potentilly be ttributed to the short NT mngement history (5 yers) nd ssocited ggregtion. However, this reson cnnot be used to explin the Colby site since it hs 15 yer NT history. Overll, cross six sites, the SWEEP model indictes crop residue removl >75% is threshold when severe wind erosion cn occur. Conclusions This study in western Knss conducted t six on-frm sites in precipittion zone rnging from 495 mm to 595 mm consistently showed tht high level of crop residue removl (>75%) incresed the soil wind erodibility t ll six sites s pproximted by severl soil prmeters. In ddition, t Colby nd Grden City, significnt soil loss cn hppen to fields with >50% crop residue removl. Significnt increse in EF, decrese in GMD, nd decrese in surfce roughness were mesured fter complete (100%) residue removl indicting tht complete residue removl is not sustinble in tht it degrdes soil structure. According to results from the SWEEP model, excessive crop residue removl (>75%) cn cuse severe soil wind 26

45 erosion for s little s three hour wind t 13 m s -1, which mkes the griculturl system unsustinble. In semi-rid regions, the mount of crop residue produced ech yer is highly dependent upon precipittion, prticulrly for rin-fed frming conditions. Even with lower residue removl levels, there my not be enough residue retined in low residue production yers to control wind erosion. Therefore, it is strongly suggested, for the future studies, long-term systemtic reserch bout permissible residue removl levels tht comprehensively considers the reltionship mong soil properties, mount of biomss retined in field, locl wether conditions, cropping system, nd crop productivity. 27

46 Figures nd Tbles Figure 1.1 Wind erodible frction (EF) (% <0.84 mm) t the L Crosse site. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. L Crosse 100% 75% 50% 25% 0% Erodible Frc-on b b b b b b b b b b b b 0 Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 28

47 Figure 1.2 Wind erodible frction (EF) (% <0.84 mm) t Rush Center. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. 60 Rush Center 100% 75% 50% 25% 0% Erodible Frc-on b b b b b b b b b b b b b b b b 0 Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 29

48 Figure 1.3 Wind erodible frction (EF) (% <0.84 mm) t Colby. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. Erodible Frc-on Colby 100% 75% 50% 25% 0% b b b b b b b b b b b Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 30

49 Figure 1.4 Wind erodible frction (EF) (% <0.84 mm) t Norctur. Tretments with different letters indicte significnt differences t the P=0.05 level. Results were seprtely compred mong tretments t ech smpling period. Erodible Frc-on Norctur b b b b b b 100% 75% 50% 25% 0% b b b b b b 0 Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 31

50 Figure 1.5 Wind erodible frction (EF) (% <0.84 mm) t Grden City. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. Erodible Frc-on Grden City 100% 75% 50% 25% 0% b b b b b b Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 32

51 Figure 1.6 Wind erodible frction (EF) (% <0.84 mm) t Scott City. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. Erodible Frc-on b b b b b Sco> City b b b b b Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time bc 100% 75% 50% 25% 0% c b b b b 33

52 Figure 1.7 Geometric men dimeter (GMD) of dry ggregtes t L Crosse. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. GMD (mm) L Crosse 100% 75% 50% 25% 0% b b b b b b b b b b b b Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 34

53 Figure 1.8 Geometric men dimeter (GMD) of dry ggregtes t Rush Center. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. GMD (mm) Rush Center 100% 75% 50% 25% 0% b bc bc c b b b b Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time bc c b bc 35

54 Figure 1.9 Geometric men dimeter (GMD) of dry ggregtes t Colby. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. GMD (mm) Colby 100% 75% 50% 25% 0% b b b b b bc c bc Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 36

55 Figure 1.10 Geometric men dimeter (GMD) of dry ggregtes t Norctur. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. GMD (mm) b Norctur 100% 75% 50% 25% 0% b b b b b b b b b Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 37

56 Figure 1.11 Geometric men dimeter (GMD) of dry ggregtes t Grden City. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. GMD (mm) b Grden City 100% 75% 50% 25% 0% b b b Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time b b b b 38

57 Figure 1.12 Geometric men dimeter (GMD) of dry ggregtes t Scott City. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. GMD (mm) b Sco> City 100% 75% 50% 25% 0% b b b b b b b b b b Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 39

58 Figure 1.13 Geometric stndrd devition (GSD) of dry ggregtes t L Crosse. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. L Crosse 100% 75% 50% 25% 0% GSD (mm) b b b b b b 0.00 Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 40

59 Figure 1.14 Geometric stndrd devition (GSD) of dry ggregtes t Rush Center. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. Rush Center 100% 75% 50% 25% 0% GSD (mm) b b b b b b b 0.00 Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 41

60 Figure 1.15 Geometric stndrd devition (GSD) of dry ggregtes t Colby. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. Colby 100% 75% 50% 25% 0% GSD (mm) b b b b b b b b b b b b 0.00 Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 42

61 Figure 1.16 Geometric stndrd devition (GSD) of dry ggregtes t Norctur. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period Norctur 100% 75% 50% 25% 0% GSD (mm) Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 43

62 Figure 1.17 Geometric stndrd devition (GSD) of dry ggregtes t Grden City. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period Grden City 100% 75% 50% 25% 0% GSD (mm) b b b b 0.00 Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 44

63 Figure 1.18 Geometric stndrd devition (GSD) of dry ggregtes t Scott City. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. GSD (mm) Sco> City 100% 75% 50% 25% 0% b b b b Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 45

64 Figure 1.19 Soil dry ggregte stbility (DAS) t L Crosse. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. Aggregte Stbility (ln J/kg) L Crosse 100% 75% 50% 25% 0% b bc bc b c Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 46

65 Figure 1.20 Soil dry ggregte stbility (DAS) t Rush Center. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. Rush Center 100% 75% 50% 25% 0% Aggregte Stbility (ln J/kg) b b b b b b bc c Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 47

66 Figure 1.21 Soil dry ggregte stbility (DAS) t Colby. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. Colby 100% 75% 50% 25% 0% Aggregte Stbility (ln J/kg) b b b b b b b b b b b Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 48

67 Figure 1.22 Soil dry ggregte stbility (DAS) t Norctur. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. Norctur 100% 75% 50% 25% 0% Aggregte Stbility (ln J/kg) b b b b Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 49

68 Figure 1.23 Soil dry ggregte stbility (DAS) t Grden City. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. Grden City 100% 75% 50% 25% 0% Aggregte Stbility (ln J/gk) Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 50

69 Figure 1.24 Soil dry ggregte stbility (DAS) t Scott City. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. Aggregte Stbility (ln J/kg) b Sco> City b b b Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 100% 75% 50% 25% 0% 51

70 Figure 1.25 Surfce rndom roughness t L Crosse. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t every site t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. L Crosse 100% 75% 50% 25% 0% 12 Roughness (mm) Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 52

71 Figure 1.26 Surfce rndom roughness t Rush Center. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t every site t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. Roughness (mm) Rush Center 100% 75% 50% 25% 0% b b Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 53

72 Figure 1.27 Surfce rndom roughness t Colby. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t every site t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. Colby 100% 75% 50% 25% 0% 12 Roughness (mm) b b c c b b 0 Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 54

73 Figure 1.28 Surfce rndom roughness t Norctur. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t every site t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. Roughness (mm) b b b b c bc Norctur 100% 75% 50% 25% 0% b bc b b b b 0 Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 55

74 Figure 1.29 Surfce rndom roughness t Grden City. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t every site t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. Grden City 100% 75% 50% 25% 0% Roughness (mm) b b b b b b b b b b 0 Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 56

75 Figure 1.30 Surfce rndom roughness t Scott City. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t every site t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. Roughness (mm) b b b Sco> City Fll 2011 Spring 2012 Fll 2012 Spring 2013 b Smpling Time 100% 75% 50% 25% 0% b 57

76 Figure 1.31 Wind erosion threshold velocity simulted by SWEEP t L Crosse. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. L Crosse 100% 75% 50% 25% 0% Ini--on Velocity (m/s) b b b b b b c c b c d d d c Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 58

77 Figure 1.32 Wind erosion threshold velocity simulted by SWEEP t Rush Center. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. The bsence of letters indictes no significnt differences mong tretments for tht prticulr smpling period. Rush Center 100% 75% 50% 25% 0% Ini--on Velocity (m/s) c b b b b b b b c c b c d d Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 59

78 Figure 1.33 Wind erosion threshold velocity simulted by SWEEP t Colby. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. Colby 100% 75% 50% 25% 0% Ini--on Velocity (m/s) d b b b b b b b c c c c d d d Fll 2011 Spring 2012 Fll 2012 Spring 2013 Axis Title 60

79 Figure 1.34 Wind erosion threshold velocity simulted by SWEEP t Norctur. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. Norctur 100% 75% 50% 25% 0% Ini--on Velocity (m/s) c b b b b b c c b d d c Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 61

80 Figure 1.35 Wind erosion threshold velocity simulted by SWEEP t Grden City. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. Ini--on Velocity (m/s) c b b Grden City d c b b b b b c c e d d Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time 100% 75% 50% 25% 0% 62

81 Figure 1.36 Wind erosion threshold velocity simulted by SWEEP t Scott City. Tretments with different letters indicte significnt differences t the p=0.05 level. Results were seprtely compred mong tretments t ech smpling period. Ini--on Velocity (m/s) c b b Sco> City c e d Fll 2011 Spring 2012 Fll 2012 Spring 2013 Smpling Time d c b 100% 75% 50% 25% 0% c b b 63

82 Figure 1.37 Precipittion in 2011, 2012, 2013 nd monthly verge t the L Crosse site. Precipit-on (mm) L Crosse verge 0 Jn Feb Mr Apr My Jun Jul Aug Sep Oct Nov Dec Month 64

83 Figure 1.38 Precipittion in 2011, 2012, 2013 nd monthly verge t the Rush Center site. Rush Center 2011 Precipit-on (mm) verge 2 0 Jn Feb Mr Apr My Jun Jul Aug Sep Oct Nov Dec Month 65

84 Figure 1.39 Precipittion in 2011, 2012, 2013 nd monthly verge t the Colby site. Colby 2011 Precipit-on (mm) verge 2 0 Jn Feb Mr Apr My Jun Jul Aug Sep Oct Nov Dec Month 66

85 Figure 1.40 Precipittion in 2011, 2012, 2013 nd monthly verge t the Norctur site. Norctur 2011 Precipit-on (mm) verge Jn Feb Mr Apr My Jun Jul Aug Sep Oct Nov Dec Month 67

86 Figure 1.41 Precipittion in 2011, 2012, 2013 nd monthly verge t the Grden City site. Precipit-on (mm) Grden City verge Jn Feb Mr Apr My Jun Jul Aug Sep Oct Nov Dec Month 68

87 Figure 1.42 Precipittion in 2011, 2012, 2013 nd monthly verge t the Scott City site. Sco> City 2011 Precipit-on (mm) verge 2 0 Jn Feb Mr Apr My Jun Jul Aug Sep Oct Nov Dec Month 69

88 Tble 1.1 Soil informtion, cropping system nd mngement of the six experimentl sites. Soil slope is < 1% t ll sites. Experimentl Cropping system (Spring 2011 Yers Totl Totl Snd Silt Soil series C:N Site Spring 2013 NT N (%) C (%) (%) (%) Cly (%) L Crosse Hrney silt lom Whet- whet- sorghum- fllow Rush Center Bridgeport silt lom Whet- whet- fllow Colby Richfield silt lom Whet- corn- fllow Norctur Ulysses silt lom Whet- corn- fllow Grden City Ulysses silt lom Whet- fllow- whet Scott City Richfield silt lom Whet- sorghum- sorghum

89 Tble 1.2 Smpling time t ech reserch site. Smpling Time Initition Time Site Fll 2011 Spring 2012 Fll 2012 Spring 2013 L Crosse My Rush Center Colby June 2011 November Mrch November Norctur Mrch Grden City Scott City 71

90 Tble 1.3 Probbility (%) of dys when wind speed reches the wind erosion threshold velocity simulted by SWEEP cross six sites mong four smpling periods. Tretments with different letters indicte significnt differences t the P=0.05 level. Results were seprtely compred mong tretments t every site t ech smpling period. Site Removl 2011 Fll 2012 Spring 2012 Fll 2013 Spring 100% % 1.66b 0.58b 0.34b 0.76b L Crosse 50% 0.29c 0.15c 0.14c 0.18c 25% 0.13c 0.23c 0.07c 0.12c 0% 0.05c 0.07c 0.02c 0.08c 100% % 0.16b 1.06b 0.11b 1.21b Rush Center 50% 0.03c 0.28c 0.01c 0.12c 25% 0.05c 0.25c 0.00c 0.06c 0% 0.02c 0.07c 0.00c 0.05c 100% % 1.77b 6.49b 6.49b 5.45b Colby 50% 0.15c 1.06c 1.91c 1.76c 25% 0.06c 0.57c 1.63c 1.27c 0% 0.02d 0.33d 1.05d 0.68d 100% % 0.25b 1.11b 0.81b 2.06b Norctur 50% 0.04c 0.22c 0.30c 0.26c 25% 0.04c 0.16c 0.22c 0.22c 0% 0.02c 0.05d 0.04d 0.13c 100% % 1.05b 5.37b 4.40b 4.12b Grden City 50% 0.59c 1.51c 1.25c 1.14c 25% 0.10d 0.87d 0.56d 0.82c 0% 0.07d 0.49d 0.47d 0.57d 100% % 0.68b 1.67b 2.41b 4.43b Scott City 50% 0.11c 0.58c 0.74c 1.65c 25% 0.09c 0.41c 0.46c 1.12c 0% 0.05c 0.36c 0.24c 0.74d 72

91 Tble 1.4 Amount of soil loss t 13 m s -1 wind speed simulted by SWEEP under 75 nd 100% removl levels t ech site. Site Removl 2011 Fll 2012 Spring 2012 Fll 2013 Spring L Crosse 100% * 1.26 * 1.36 * 75% Rush Center 100% * 1.19 * % Colby 100% * % Norctur 100% * 75% Grden City 100% * * 75% Scott City 100% 1.37 * 2.38 * 1.36 * 1.41 * 75% * Soil losses re bove the NRCS tolerble soil loss limit of 1.12 kg m -2 for the study soils. 73

92 Tble 1.5 Probbility (%) of wind speed 13 m s -1 t the nerest wether sttion from ech study site in ech month. Reserch Site Nerest Wind Sttion County Jn Feb Mr Apr My Jun Jul Aug Sep Oct Nov Dec L Crosse & Rush Center Hys Municipl (AWAS) Ellis Colby Goodlnd/Renner (AW) Thoms Norctur US NE McCook Dectur Grden City & Scott City Grden City Municipl Finney

93 References Allmrs, R.R., R.E. Burwell, W.E. Lrson, nd R.F. Holt Totl porosity nd rndom roughness of the interrow zone s influenced by tillge. USDA Cons. Res. Rpt. 7. Arshd, M. A., Frnzluebbers, A. J., Azooz, R.H., Components of surfce soil structure under conventionl nd no-tillge in northwest Cnd. Soil Till Res. 53: Benymini, Y. nd Unger, P. W Crust development under simulted rinfll on four soils. In: gronomy Abstrcts. P ASA, Mdison, WI. Bielders, C. L., Michels, K., nd J. L. Rjot, On-frm evlution of ridging nd residue mngement prctices to reduce wind erosion in Niger. Soil Sci. Soc. Am. J. 64: Bilbro, J. D., nd Fryrer, D. W Plnt mteril for windbrriers in semirid regions. p In Proc. Wind Erosion Conference, Lubbock, TX. April 11-13, Blnco-Cnqui, H Energy Crops nd Their Implictions on Soil nd Environment Agron. J. 102: Blnco-Cnqui, H., Ll, R., Post, W. M., Izurrlde, R. C., nd Owens, L. B Soil structurl prmeters nd orgnic crbon in no-till corn with vrible stover retention rtes. Soil Sci. 171: Blnco-Cnqui, H., nd Ll, R Crop residue removl effects on soil productivity nd environmentl qulity. Crit. Rev. Plnt Sci. 28: Blnco-Cnqui, H., nd Ll, R. 2009b. Corn Stover removl for expnded uses reduces soil fertility nd structurl stbility. Soil Sci. Soc. Am. J. 73: Boyd, D. W., Skidmore, E. L., nd Thompson, J. G., A soil-ggregte crushing-energy meter. Soil Sci. Soc. Am. J. 47: Brid, J. A., Reichert, J. M., d Veig, M., nd Reinert, D. J Mulch nd soil orgnic crbon content nd their reltionship with the mximum soil density obtined in the proctor. Rev. Brsileir De Cienc. Do Solo 30: Bullock, M. S., Lrney, F. J., Izurrlde, R. C., Feng, Y., Overwinter chnges in wind erodibility of cly lom soils in southern Albert. Soil Sci. Soc. Am. J. 65, Buschizzo, D. E. nd Zobeck, T.M., Vlidtion of WEP, RWEQ nd WEPS wind erosion for different rble lnd mngement systems in the Argentinen Pmps. Erth Surf. Process. Lndforms 33: Chn C. K. nd Yo X., Air pollution in meg cities in Chin. Atmospheric Environment 42:

94 Chepil, W. S., Dynmics of wind erosion: I. Nture of movement of soil by wind. Soil Sci. 60: Chepil, W. S., Improve rotry sieve for mesuring stte nd stbility of dry soil structure. Soil Sci. Soc. Am. Proc. 26:4-6. Chepil, W.S., A compct rotry sieve nd the importnce of dry sieving in physicl soil nlysis. Soil Sci. Soc. Am. J. 1962, 26, 4 6, doi: /sssj x. Colcicco, D., Osborn, T., nd Alt, K Economic dmge from soil erosion. J. Soil Wter Conserv. 44: Colzo, J. C., nd Buschizzo, D. E., Soil dry ggregte stbility nd wind erodible frction in semirid environment of Argentin. Geoderm 159: Dm, R. F., Mehdi, B. B., Burgess, M.S.E., Mdrmootoo, C.A., Mehuys, G.R., Cllum, I.R., Soil bulk density nd crop yield under eleven consecutive yers of corn with different tillge nd residue prctices in sndy lom soil in centrl Cnd. Soil Till. Res. 84: Devine, S., Mrkewitz, D., Hendrix, P., nd Colemn, D Soil Aggregtes nd Associted Orgnic Mtter under Conventionl Tillge, No-Tillge, nd Forest Succession fter Three Decdes. PLoS ONE 9(1): e doi: /journl.pone Evers, B. J., Blnco-Cnqui, H., Stggenborg, S. A., nd Ttrko, J Dedicted bioenergy crop impcts on soil wind erodibility nd orgnic crbon in Knss. Agronomy Journl. 105(5): Feng, G. nd Shrrtt, B Evlution of the SWEEP model during high winds on the Columbi Plteu. Erth Surfce Processes nd Lndforms 34: Erth Surfce Processes nd Lndforms 34: Gee, G.W., nd Buder, J.W Prticle-size nlysis. In: A. Klute (Editor), Methods of Soil Anlysis, Prt 1. Agronomy, 9: Grhm, R. L., Nelson, R., Sheehn, J., Perlck, R. D., nd Wright, L. L Current nd potentil U.S. corn stover supplies. Agron. J. 99: Hgen, L. J., A wind erosion prediction system to meet user needs. Jour. Soil nd Wter Comerv. 46(2): Hgen, L.J., Skidmore, E.L., nd Sleh, A Wind Erosion: Prediction of Aggregte Abrsion Coefficients. ASAE J. 35(6): Hgen, L.J., Wgner, L.E. nd E.L. Skidmore Anlyticl solutions nd sensitivity nlyses for sediment trnsport in WEPS. Trns. Amer. Soc. Agric, Engin. 42(6):

95 Hill, R.L., Long-term conventionl nd no-tillge effects on selected soil physicl properties. Soil Sci. Soc. Am. J. 54: Hobbs, P.R., Conservtion griculture: wht is it nd why is it importnt for future sustinble food production? Journl of Agriculturl Science. 145: Ji, Q., Al-Ansri, N., Knutsson, S Modeling of Wind Erosion of the Aitik Tilings Dm Using SWEEP Model. Engineering. 6(7). DOI: /eng Kenney, I., Blnco-Cnqui, H., Presley, D.R., Rice, C.W., Jnssen, K., nd Olson, B Soil nd crop response to stover removl from rinfed nd irrigted corn. Globl Chnge Biology Bioenergy, doi: /gcbb Kim, S., nd Dle, B.E Globl potentil bioethnol production from wsted crops nd crop residues. Biomss Bioenerg. 26: Krvchenko, A.N., Robertson, G.P., Ho, X., Bullovk, D.G., Mngement prctices effects on surfce totl crbon: differences in sptil vribility ptterns. Agron. J. 98: Ll, R., No-till frming: soil nd wter conservtion nd mngement in the humid nd subhumid tropics. IITA Monogrph No.2, IITA, Ibdn, Nigeri, 64pp. Ll, R., Soil crbon sequestrtion impcts on globl climte chnge nd food security. Science. 304: Ll, R Soil qulity impcts of cresidue removl for bioethnol production. Soil & Tillge Reserch. 102: Lrney, F.J., Bullock, M.S., Jnzen, H.H., Ellert, B.H., nd Olson, E.C.S Wind erosion effects on nutrient redistribution nd soil productivity. J. Soil nd Wter Cons. 53: Lyton, J.B., E.L. Skidmore, nd C.A. Thompson Winter-ssocited chnges in dry-soil ggregtion s influenced by mngement. Soil Sci. Soc. Am. J. 57: Leys, J. nd NcTinsh, G Soil loss nd nutrient decline by wind erosion cuse for concern. Aust. J. Soil & Wter Conserv. 7(3): Li, F., Zho, L., Zhng, H., Zhng, T., Shirto, Y., Wind erosion nd irborne dust deposition in frmlnd during spring in the Horqin Sndy Lnd of estern Inner Mongoli, Chin. Soil Tillge Res. 75: Lyles, L., Dickerson, J.D., nd Disrud, L.A., Modified rotry sieve for improved ccurcy. Soil Sci. 190: Lyles, L., nd B.E., Allison Equivlent wind-erosion protection from selected crop residues. Trns ASAE. 24:

96 Mendez, M.J., nd Buschizzo, D.E Wind erosion risk in griculturl soils under different tillge systems in the semirid Pmps of Argentin. Soil Tillge Res. 106: Mengel, D.B., Wilson, D.W., Huber, D.M., Plcement of nitrogen fertilizer for no-till nd conventionl tillge corn. Agron. J. 74: Nelson, R. G., Wlsh, M., Sheehn, J. J., nd Grhm, R Methodology for estimting removble quntities of griculturl residues for bioenergy nd bioproduct use. Applied Biochemistry nd Biotechonology 113: Okin, G.S., Mhowld, N., Chdwick, O.A., nd Artxo, P Impct of desert dust on the biogeochemistry of phosphorus in terrestril ecosystems. Globl Biogeochemicl Cycles, 18, GB2005, doi: /2003gb Perlck, R.D.; Wright, L.L.; Turnhollow, A.F.; Grhm, R.L.; Stokes, B.J.; Erbch, D.C Biomss s feedstock for bioenergy nd bioproducts industry: the technicl fesibility of billion-ton nnul supply. Ok Ridge, TN: Ok Ridge Ntionl Lbortory. 59 p. Rhoton, F. E Influence of Time on Soil Response to No-Till Prctices. Soil Sci. Soc. Am. J. 64: Rhoton, F. E., Shipitlo, M. J., nd Lindbo, D. L Runoff nd soil loss from midwestern nd southestern US silt lom soils s ffected by tillge prctice nd soil orgnic mtter content. Soil Tillge Res. 66: Run, H. X., Ahuj, L. R., Green, R. R., nd Benjmin, J. G Residue cover nd surfceseling effects on infiltrtion: numericl simultions for field pplictions. Soil Sci. Soc. Am. J. 65: Slib N. A., El Jm F., El Tyr G., Obeid, W., nd Roumie M., Atmospheric Reserch 97: Srth, G., Mitchell, R. B., Sttler, S. E., Funnell, D., Pedersen, J. F., Grybosch, R. A., nd Vogel, K. P Opportunities nd rodblocks in utilizing forges nd smll grins for liquid fuels. J. Ind. Microbiol. Biotechonol. 35: SAS Institute (2011) Online doc SAS Institute Inc., Gry, NC. Avilble t (verified 21 Jn. 2015). Schwnghrt W., nd Schutt B., Meteorologicl cuses of Hrmttn dust in West Afric. Geomorphology 95: Six, J., Elliott, E.T., nd Pustin, K Aggregte nd Soil Orgnic Mtter Dynmics under Conventionl nd No-Tillge Systems. Soil Sci. Soc. Am. J. 63: Skidmore E.L, Hgen L.J., Armbrust D.V., Durr A.A., Fryrer D.W., Potter K.N., Wgner L.E., nd Zobeck T.M Methods for investigting bsic processes nd conditions 78

97 ffecting wind erosion. In Soil Erosion Reserch Methods, L1 R (ed.). Soil nd Wter Conservtion Society: Ankeny, IA; SPSS Science SigmScn Pro 5.0 User s Guide. SPSS Science, Chicgo, IL. Ttrko, J., Wgner, L.E., Boyce, C.A Effects of Overwinter Processes on Stbility of Dry Soil Aggregtes. Soil Erosion Reserch for the 21 st Century, Proc. Int. Symp. (3-5 Jnury 2001, Honolulu, HI, USA): Vrvel, G.E., Vogel, K.P., Mitchell, R.B., Follett, R.F., Kimble, J.M., Comprison of corn nd switchgrss on mrginl soils for bioneregy. J Biomss nd Bioenergy 32: Wgner L.E., nd Ding, D Representing ggregte size distributions s modified lognorml distributions. Trnsctions of the ASAE 37(3): Wgner, L.W. nd Yu, Y Digitiztion of profile meter photogrphs. Trns. Am. Soc. Agric. Engin. 34(2): Wgner, L.E A history of wind erosion prediction models in the United Sttes Deprtment of Agriculture: The Wind Erosion Prediction System (WEPS). Aeolin Reserch. 10:9-24. Wng, L., Shi, Z.H., Wu, G.L., nd Fng, N.F Freeze/thw nd soil moisture effects on wind erosion. Geomorphology. 207: Wilhelm,W.W., Johnson, J. M. F., Htfield, J. L., Voorhees,W. B., nd Linden, D. R Crop nd soil productivity response to corn residue removl: literture review. Agron. J. 96: Wilhelm, W.W., Johnson, J.M.F., Krlen, D., nd Lightle, D Corn stover to sustin soil orgnic crbon further constrins biomss supply. Agron. J. 99: Wuest, S.B., Cesr-TonTht, T.C., Wright, S.F., Willims, J.D., Orgnic mtter ddition, N, nd residue burning effects on infiltrtion, biologicl, nd physicl properties of n intensively tilled silt-lom soil. Soil Till. Res. 84 (2): Zobeck, T.M., nd Bilbro, J.D Crop Productivity nd Surfce Soil Properties of Severely Wind-Eroded Soil. In D.E. Stott, R.H. Mohtr nd G.C. Steinhrdt (eds). Sustining the Globl Frm. 10th Interntionl Soil Conservtion Orgniztion Conference. My 24-29, Purdue University nd the USDA-ARS Ntionl Soil Erosion Reserch Lbortory

98 Chpter 2 - Effect of Liquid N nd S Fertilizer Solutions on the Mss nd Strength of Winter Whet (Triticum estivum) Residue in No-Till Systems Abstrct To solve stnd estblishment issues in high residue situtions, ppliction of nitrogen (N) fertilizer s ure mmonium nitrte (UAN) nd N plus sulfur (S) fertilizer s mmonium thiosulfte (ATS) by sprying on crop residue to stimulte microbil ctivity nd subsequent decomposition of the residue is often debted. We conducted field experiments to ssess winter whet (Triticum estivum) strw decomposition under different fertilizer rtes nd ppliction timings t three loctions in western Knss (Hys, Colby, nd Grden City) following whet hrvest in 2011 nd The UAN ws pplied t rtes of 0, 22.4, 44.8 nd 67.2 kg N h -1 nd the ATS ws pplied t rtes of 16.8 nd 33.6 kg S h -1. A double sher box pprtus instrumented with lod cell mesured the sher stress required to cut whet strw. Twenty-five whet strws from ech plot were tested. Photomicrogrphy nd imge nlysis softwre were used to mesure the cross-sectionl re of ech individul whet strw fter shering nd these dt were used to clculte sher stress nd specific energy prmeters. Totl C nd N content ws mesured for bulk whet strw smples from ech plot. Tretment differences were often observed; however, there were few site yers tht hd significnt differences in whet strw decomposition s compred to the no-fertilizer control. For exmple, fertilizer rte nd timing of ppliction during summer 2012 nd Fll 2013 t the Hys site hd impcts on whet strw sher stress t brek point. Across site yers, erlier (fll) fertilizer ppliction generlly resulted in lower remining boveground biomss s compred to spring ppliction. Multivrite nd 80

99 liner regressions suggested tht N content nd C:N rtio cn explin the results observed with respect to tretment effects on winter whet residue decomposition. Introduction The importnce of crop residue to soil qulity nd gronomic sustinbility is widely recognized by reserchers nd frmers. The benefits of no-till (NT) prctices include tht it mintins high levels of crop residue on the ground, enhnces soil structure, conserves soil moisture, mintins soil nutrient pools, protects plnt growth, nd increses griculturl productivity (Unger, 1994; Hobbs, 2007). Incresingly, producers re switching to NT mngement in the U.S. (112.8 million hectres NT in 2012), prticulrly in rin-fed res where soil moisture is highly dependent on precipittion (USDA, 2014). Compred to conventionltillge (CT), NT or reduced tillge (RT) my increse surfce soil wter content (Ll, 1982; Mengel et l., 1982), enhnce soil ggregte stbility (Dm et l., 2005; Hobbs, 2007), increse soil mechnicl resistnce (Reichert et l., 2009), nd generlly hve higher bulk density (Hill, 1990; Dm et l., 2005; Krvchenko et l., 2006). Horton et l. (1996) stted tht NT systems retining crop residue could increse the lbedo of the soil surfce, which hs implictions for helping mitigte climte chnge. Using the Consortium for Smll-scle Modeling-Climte Limited-re Modeling Regionl Climte Model, Dvin et l. (2014) found 2 cooling effect due to NT prctices. Globl whet production ws expected to rech 690 million tons in 2013, which ws 4.3 percent increse over the previous yer (FAO, 2013). Although whet strw is potentil feedstock for bioenergy production (Srth et l., 2008), Blnco-Cnqui nd Ll (2009) concluded tht indiscriminte removl of crop residue could drsticlly reduce the erosionresisting benefits of NT frming. This is prticulrly true for semi-rid res. Therefore, crop 81

100 residue often remins in the field fter hrvest to decrese the potentil for losses of soil by wind erosion in some regions tody (Go et l., 2014). One direct effect of NT is tht lrge mount of crop residue remins on the ground fter crops re hrvested, prticulrly in high-yielding environments or in yers of bundnt rinfll nd idel growing conditions. Frmers my hve concerns bout estblishing good plnt stnd in high residue situtions due to higher sher stress nd energy required to cut through residues by the disk opener on plnters or drills (Pyton et l. 1985; Don et l., 2005). Decomposed crop residue tends to hve weker structure (McCll, 1943; Annoussmy et l., 2000). However, dry regions hve climte tht is not s conducive to residue decomposition s more humid regions (Schomberg et l., 1994; Aber et l., 2014). Therefore, incresing the decomposition rte of whet strw between post-hrvest nd plnting could be n effective wy to solve bundnt crop residue issues while mintining the benefits of residue coverge. Usully, cerel crop residues hve high crbon (C) to nitrogen (N) rtio (C:N) (Hds et l., 2004; Hvstd et l., 2010). Significntly higher C:N rtio in whet strw (up to 55.1) compred to seed ws mesured by Gn et l. (2011). According to the literture, bout 32.5% of the cells in whet strw re fibers nd the remining 67.5% contins prenchym, epidermis cells, vessels, nd spirls, known s non-fibrous cells (Singh et l., 2011). Li et l. (2009) observed tht the structurl degrdtion of whet strw hppened minly in the prenchym cells nd the surrounding vsculr bundles 50 dys fter study ws initited. Due to the selection of vrieties with better lodging resistnce, stiffer nd shorter strw whet is preferred (Trvis et l., 1996). Cpper et l. (1992) reported tht these vrieties usully contin high lignin content with low digestibility. Menwhile, Kriučiūnienė et l (2012) found tht highly decomposed residue hd significntly higher concentrtion of N compred to less decomposed residue. Therefore, dding 82

101 N fertilizer to lower the C:N rtio (Melchiori et l., 2014) hs the potentil to hsten whet strw decomposition fter grin hrvest. During the decomposition process, not only cn N content be the limiting fctor tht restricts the bioctivity of microbiomss, but lso my cuse N immobiliztion from soil nd dditionlly decrese the nutrient pool in soil for the next crop (Clpp et l., 2000). Menwhile, s secondry nutrient, sulfur (S) cn be limiting fctor, especilly fter hrvest of high S demnd plnts such s lflf. Consequently, one thought n gronomist or producer might hve is to pply these limiting nutrients (N nd/or S) to the residue to stimulte microbil ctivity nd subsequent decomposition of the residue. However, there is no consensus mong reserchers on the utility of this prctice. A recent pper by Guzmn nd Alkisi (2013) exmined the effects of tillge nd dding N fertilizer on the decomposition rtes of Bt nd non-bt corn observing no significnt differences between Bt nd non-bt isolines under NT mngement. Also, they did not observe difference in the decomposition rtes between Bt nd non-bt; however, mize residue decomposition rtes declined with incresing N rtes. A double sher using sher box is the method tht cn be used to evlute sher strength of crop residue. O Dogherty et l. (1989) reported rnge of 5.39 to 6.98 MP sher stress for winter whet strw ws smller thn spring whet strw, which ws 8.53 MP. Dernedde (1970) pplied this method to test sher strength of forge mterils t two different moisture contents. Similrly, Kushh et l. (1983) found the sher strength of whet strw hd reltionship with the moisture content. Tvkoli et l. (2009) tested the brley strw t different internodes nd reported the third internode position of brley strw hd the mximum sher strength. Tghijrh et l. (2011) pplied the double sher method on sugr cne stlk nd reported the loding rte nd internode position hd significnt impcts on the shering chrcteristics. However, the 83

102 reltionship between whet strw decomposition due to different fertilizer tretments nd its physicl strength prmeters (i.e. sher stress, specific energy) hs not been documented. The objective of reserch ws to evlute the effect of ppliction rte nd timing of two commercilly-vilble liquid fertilizers (i.e., Ure Ammonium Nitrte (UAN) nd Ammonium Thiosulfte (ATS) on the decomposition of whet strw by mesuring physicl strength prmeters, nd nlyzing for totl C, N, nd sh percent of strw fter tretment. Mterils nd methods Site description nd field experimentl protocols Three reserch sites were estblished in western Knss in 2011 nd 2012 fter winter whet hrvest. Sites were t Hys ( N, W, elevtion 616 m), Colby ( N, W, elevtion 963 m), nd Grden City ( N, W, elevtion 883 m). The experimentl design ws rndomized complete block design with four replictions. All plots were 6.1 m 6.1 m in size nd were plced directly over the center of the grin hrvesting equipment pth (i.e., between the wheel trcks). The UAN ws pplied t rtes of 0, 22.4, 44.8 nd 67.2 kg N h -1 nd the ATS ws pplied t rtes of 16.8 nd 33.6 kg S h -1. The ATS lso contined 7.7 nd 15.5 kg N h -1. Herefter the fertilizer rtes will be referred to s UAN low/med/high, nd ATS low/high respectively. In ddition, there ws one tretment tht contined blend of UAN high nd ATS high, referred to s Mixed, which contins 82.7 kg N h -1 nd 33.6 kg S h -1. All fertilizer tretments were pplied using trctor-mounted spryer using flt fn spry tip. No wter or surfctnts were used. The fertilizers were pplied t two different times to seprte plots, resulting in totl of 13 tretments (Tble 2.1). The two ppliction times were 84

103 September, fter whet hrvest, nd Februry, before tempertures incresed nd microbil ctivities resumed. Residue smpling nd nlyses Whet strw smples were collected from within portion of ech reserch plot in 0.61 m 0.61 m re in summer (July) 2012, summer (June) 2013, nd fll (October) 2013 from the Hys nd Colby sites. The Grden City site ws only smpled in summer 2012 nd summer 2013 due to very poor residue conditions from high wind speeds tht lodged nd blew nerly ll of the whet residue off of the field. The residue smpling periods were selected to simulte the time of yer when subsequent crops would normlly be plnted, e.g., whet in fll, nd row crops such s corn (Ze mys L.) in the spring. The whet strw ws sorted by hnd to remove ny soil mteril tht my hve been collected from the field. Strw smples were dried t 56 for 72 h nd weighed to clculte totl surfce residue. A subsmple of 25 whet strws were rndomly selected for the shering test nd the reminder of the strw smple ws then ground nd nlyzed for totl C, totl N (Bremner nd Mulvney, 1982) nd sh percent (Khrdiwr et l., 2013). A double sher using sher box ws used to test the sher stress nd specific energy required to cut whet strw. Dernedde (1970), O Dogherty et l. (1989), Shinner et l. (1987), nd Tghijrh et l. (2011) pplied similr method to mesure the sher strength of crop residue or plnt tissue. This process is intended to simulte the type of force encountered by disk opener on drill or plnter s it cuts through crop residue. Figure 2.1 shows the design of the sher box. The sher box consists of two prllel luminum pltes (chnnel) 6 mm prt. Between them, the third plte (blde) cn move up nd down long the centrl xis freely. Five holes with dimeters rnging from 2 mm to 6 mm were drilled through ll three pltes to 85

104 ccommodte different whet strw sizes. The sher box ws ttched to the Instron MN 44 (Instron, Norwood, MA), lod cell of tension/compression testing mchine (Fig. 2.2). The blde plte ws set to move t rte of 10 mm min -1 nd the pplied force ws recorded by strin-guge lod cell. Integrting the sher force with the respect to the displcement untill the filure force (Fig. 2.3) genertes the totl energy (TE) used to cut through whet strw (Chen et l., 2004; Nzri Gledr et l., 2008). The specific energy ws then clculted s: SE = TE A Where SE is the specific energy (J mm!! ) TE is the totl energy (J) A is the whet strw wll re t filure cross-section (mm 2 ) The sher stress ws then clculted s: τ! = F 2A Where τ! is the sher stress (MP) F is the sher force t filure (N) A is the whet strw wll re t filure cross-section (mm 2 ) 86

105 Sub-smples from ech plot were tested for τ! nd SE in this mnner. During the shering test, sher force ws recorded by the computer. Sher force chnge with the center blde movement ws then grphed (Fig. 2.3). Figure 2.3 illustrtes n exmple output from the lod cell. The highest lod ws reported by the computer, which is the shering force (F) t the point of whet strw filure, s well s TE. To ccurtely mesure the cross-sectionl re t the breking point of whet strw, microscope nd cmer ws utilized to cpture imges of the cross-sectionl re of whet strw. The pictures were then nlyzed with SigmScn 5 (Systt Softwre Inc.) imge nlysis softwre. Figure 2.4 shows the whet strw cptured by microscope (left) nd then nlyzed with the softwre to determine the re (right). Sttisticl nlysis Anlysis of vrince ws conducted using SAS 9.3 (SAS Institute, 2011) softwre nd summrized. MIXED procedure using tretment nd time s clssifiction vribles for two-wy nlysis of vrince, REG procedure using physicl prmeters s dependent vrible nd totl C, N, nd sh content s independent vribles for multivrite stepwise regression, nd REG procedure using physicl prmeters s dependent vrible nd C:N rtio s independent vrible for liner regression were pplied to nlyze the dt. Results Results of sttisticl nlysis were shown from Tble 2.2 to Tble 2.4. The p-vlues from two-wy nlysis of vrince t α 0.05 nd α 0.10 re presented in Tble 2.2. The sterisks indicte properties tht hd significnt tretment differences within smpling period. Multiple regression results of reltionships between physicl (i.e. SE nd τ! ) nd chemicl (i.e. totl C, N, 87

106 nd sh content) prmeters re reported in Tble 2.3. Liner regression results between physicl prmeters nd C:N rtio re shown in Tble 2.4. Aboveground biomss For summer 2012 smples, the fertilizer ppliction timing hd significnt effects (p 0.1) on the boveground biomss t Colby (Tble 2.2). There were no significnt tretment differences mesured t Hys nd Grden City sites for the summer 2012 smpling period. Figure 2.5 shows effects of the tretments on the whet strw biomss in summer 2012 t the Colby site under different tretments. Besides the spring 2012 tretment, the boveground biomss tht remined in the other plots ws not significntly different from the control. The ppliction of UANlow in spring 2012 hd significntly greter biomss remining in the field compred to the fll 2011 ppliction of the sme tretment. Also, pplictions of ATShigh nd the mixture of the two fertilizers in fll 2011 hd significntly less boveground biomss compred to the UAN low ppliction in spring Significnt residue biomss differences due to the fertilizer types nd rte were lso mesured t both the Hys nd Colby sites during the Summer 2013 smpling period (Fig. 2.5). Although there is no significnt difference between the control nd ny tretment t Hys (Fig. 2.5), the overll biomss of the fll 2012 pplied tretments ws less thn spring 2013 ppliction (p<0.01), when verged cross ll fertilizer types nd rtes (Tble 2.2). Significntly different biomss between ppliction timings under sme mount fertilizer usge ws only mesured t UANmed tretment t this site. A similr pttern ws observed t the Colby site. Timing of the ppliction ws significnt, nd the fll 2012 ppliction led to less remining biomss thn the spring 2012 timing (p<0.01). Compred to the control, UANmed nd ATShigh pplied in fll 2012 led to significntly less boveground biomss. Between different timings 88

107 with sme mount of fertilizer ppliction, UANmed pplied in fll 2012 led to significntly less reimgining biomss thn when pplied in spring During the Fll 2013 smpling period, there were no tretment effects mesured t either the Hys or Colby sites. For the Grden City site, compred to the control, no significnt difference in boveground biomss ws mesured for the fll 2012 smpling period. Physicl evlution of strw strength Specific Energy (SE) Significnt tretment effects were observed for the SE mesurement for the smples tken from Hys in summer 2012 nd Fll 2013 nd t Grden City in summer At Hys in the summer of 2012, both fertilizer rte nd timing fctors contributed to the SE required to cut through the whet strw. As shown in Figure 2.6, the men SE required to sher the control group smples ws ! J m -2, while the energy required to cut through UANlow is significntly less, t ! J m -2. Although significnt timing effect on SE ws only mesured t Hys during summer 2012 smpling period (p<0.05), generlly, the spring tretments required lower energy to brek whet strw compred to fll-pplied tretments t ll sites. However, most of the tretments were not significntly different from the control, except the UANlow tretment. Similr results were found t Grden City, in tht UANlow nd ATSlow tretments led to significntly lower SE compred to the control (p<0.01). At Hys in Fll 2013, significntly lower SE ws mesured under UANlow nd UANhigh tretments pplied in both fll 2012 nd spring 2013, nd ATShigh tretment pplied in spring 2013 compred to control group. At the Grden City site, SE mesured for the UANlow tretment pplied in fll 2011 ( J m -2 ) ws significntly lower thn the control ( J m -2 ). 89

108 Sher Stress (τ s ) For the Hys summer 2012 smpling period, the ppliction time ws not significnt, nor were there ny prticulr tretments tht hd lower τ! thn the control. There were some minor differences mong tretments, however (p=0.05), such s the decresing τ! with incresing rtes of UAN (Fig. 2.7). For the Fll 2013 smpling period t the Hys loction, there were tretments with significntly less τ! thn the control. In prticulr, the strw smpled from ll three of the UAN rte tretments ws weker by 20% thn the control. Generlly, whet strw from plots with fll 2012 ppliction required less τ! to sher the strw (p<0.05). There were no differences between the control nd either of the ATS tretments, nor the mixed tretment. As shown in Figure 2.7, t Colby in summer 2012, there ws only one tretment tht differed from the control. The whet strw from the fll-pplied Mixed tretment required significntly less τ! (3.58 Mp) to cut through compred to the control tretment (4.44 Mp). Chemicl prmeters of whet strw Totl C Significnt differences were not observed between tretments for either the summer 2012 or the Fll 2013 smpling period. However, during the Summer 2013 smpling period, significnt tretment effects were detected t ll three sites: Hys, Grden City (p<0.05), nd Colby (p<0.1) (Fig. 2.8). The Hys site hd significnt tretment*timing interction (p=0.09). Timing ws not significnt t either the Grden City or Colby sites. The C content ws lower for both UANlow nd ATSlow. 90

109 Reltive to the control, the C content for Hys 2013 smples ws less for both the UANlow nd ATSlow tretments nd for both the fll nd spring pplictions. Among ll of the tretments, ATSlow with fll 2012 ppliction tretment hd lest C content of ll, which ws 394 g kg -1 compred to 414 g kg -1 mesured for the control. The vlues from Colby nd Grden City (Fig. 2.8) were not different from the control. However, there were tretments tht differed from ech other. For exmple, t the Colby site, the lest C content ws observed for ATShigh pplied t fll At the Grden City site, the lest C content ws for UANlow pplied t spring 2013 tretment. Totl N The results of N concentrtion of whet strw re shown in Figure 2.9. For the fll 2012 smpling intervl t Hys, there ws significnt effect of the timing of liquid fertilizer. All of the fll-pplied fertilizer tretments contined the sme N concentrtion s the control, while two of the spring-pplied tretments contined more N thn the control. For the Hys 2013 experiment, however, there ws no timing effect, but rther tretment effect, with the mid-rte of UAN nd high rte of ATS contining more N thn the control. Timing ws lso n importnt fctor for the Grden City summer 2012 site. The fll pplied tretments contined less N thn the spring pplied tretments (p=0.05). C:N Rtio For the summer 2012 smpling period there were significnt ppliction timing effects for both Hys nd Grden City (Fig. 2.10), nd for both sites, the spring pplictions hd nrrower C:N thn tretments pplied in the fll. Conversely, in Summer 2013 there ws no effect of timing on ny of the sites, but there were significnt tretment effects t both Hys nd Grden City. The UANlow nd UANmed hd nrrower C:N rtio compred to the control t Hys, 91

110 while t Grden City, there were no differences from the control. Rther, t Grden City, the min differences were between tretments. The UANhigh fll nd spring tretments were mong the lowest with C:N vlues of <40:1, nd the ATS fll nd spring vlues were gretest for the ATShigh tretment. Ash Content Significnt effects of the fertilizer sources/rtes on whet strw sh content were observed for Colby nd Grden City in Summer 2013 (Fig. 2.11). Among them, the Colby site hd tretment*timing interction s well. At Colby, the sh content of the ATShigh tretment pplied in fll 2012 (15.1%) ws significntly greter thn the control (10.2%). At Grden City, no sttisticl difference of sh content ws mesured between ny tretments s compred to the control. However, tretment differences existed. Multiple regression: Exmining reltionships between physicl nd chemicl properties Significnt effects of totl N content on SE required to cut through whet strw were found t three out of seven smpling periods (Tble 2.3), which were the summer 2012 smples t Hys (p < 0.1) nd Grden City (p < 0.05) (inverse reltionship), nd Fll 2013 smple t Colby (p < 0.05) (positive reltionship). The coefficient of determintion (R 2 ) for three smpling periods rnges from 0.08 to 0.22 (Tble 2.3). Smples collected in Summer 2013 from Hys were inversely relted with respect to totl C content nd SE required (P=0.02). A negtive reltionship ws reported nd the coefficient of determintion is 0.1. Significnt impcts of totl N content on τ! were mesured for six out of seven smpling periods (Tble 2.3), ll with negtive reltionships between N nd τ!. Menwhile, significnt effects of totl C content on τ! were found t Hys in Summer 2013 nd Grden City in summer 92

111 2012 (Tble 2.3). Similr to the SE, n inverse reltionship ws observed between C nd τ!. Additionlly, the coefficient of determintion rnged from 0.13 to Simple liner regression between physicl prmeters nd C:N rtio A significnt reltionship between the C:N rtio nd SE required to cut through whet strw ws mesured t three out of seven smpling periods. Among them, smples from Hys nd Grden City in summer 2012 showed positive reltionship. However, smple from Colby in Fll 2013 were negtively relted. The coefficients of determintion rnged from 0.07 to Five out of seven smpling periods showed significnt effects of C:N rtio to τ! mesured to cut through whet strw. They re Hys nd Grden City in summer 2012, Colby in Summer 2013, nd Colby nd Hys in Fll All five smpling periods hd positive reltionships between τ! nd the C:N rtio. The coefficient of determintion rnged from 0.10 to Discussion In situ ppliction of fluid N nd N plus S fertilizer hd inconsistent effects in this study. Tble 2.2 summrizes the inconsistency of the tretment nd timing effects for sum of eight smpling periods over the course of the two-yer, three loctions, nd three smpling periods project (minus the Grden City smpling period tht ws not completed). For the biomss prmeter, there were no significnt fertilizer tretment effects; however, timing ws significnt for three out of the eight dt sets. In yers with significnt effect of timing, fll ppliction resulted in less remining biomss thn the spring ppliction of liquid fertilizers on whet strw, which indictes tht whet strw decomposition my be positively correlted to the length of time tht hs pssed since liquid fertilizer ws pplied. 93

112 Annoussmy et l. (2000) studied the chnge in whet strw mechnicl properties nd found 40% decrese in biomss due to decomposition nd lso mesured lower physicl strength (i.e., shering force nd bending force). In our study, the strength prmeters, SE nd τ!, hd few instnces of tretment or timing difference. Both timing nd fertilizer ppliction rte ffected SE significntly for one out of the eight site yers. However, interction between these two fctors ws found s well. Significnt effects of fertilizer ppliction rte nd timing on whet strw τ! were found for two of the eight dt sets. Fctors tht cn ffect in situ boveground biomss include initil post-hrvest biomss, locl wether condition (i.e., temperture, precipittion, moisture, nd wind etc.), nd residue decomposition rte (Kriučiūnienė et l., 2012; Al-Kisi nd Guzmn, 2013). In western Knss, where the study ws conducted, wind erosion is mjor concern. Whet strw cn be detched nd removed from the field by strong wind regrdless if it is physiclly wekened due to the decomposition. At the Grden City site, we hd to exclude the Fll 2013 smpling period due to strong winds nd physicl loss of residue cross the entire field. Therefore, when wind velocity is excessively high, impct of the decomposition on residue boveground biomss my not be cler. In other words, the effects of tretments nd our bility to detect differences my be confounded with field conditions such s intense precipittion nd strong wind. To simulte the disk opener of the plnter nd how it encounters residue during plnting, we rndomly selected whet strw internode position (i.e. section from root) for the shering test. To determine size of the sub-smple needed, we tested 50 strws for physicl prmeters from two bseline smples nd sttisticlly nlyzed results for 10, 20, 30, 40 nd 50 strws (Tble 2.6) nd found tht there ws no difference when more thn 20 smples were tested. Therefore, we elected to test 25 whet strws from ech smple. However, verging the physicl strength 94

113 results of sub-smple from ech plot might offset the vrious degrees of impcts of fertilizer ppliction rtes nd timings on different section of whet strw. Huber (1991) stted tht different internodes of whet hd different cross-sectionl re nd mss per unit length. Therefore, different SE nd τ! could be expected to be mesured for different internodes of ny one whet strw. Annoussmy et l. (2000) found significnt effects of mss per unit length or cross-sectionl re on whet strw physicl strength. Consequently, the inconsistent decrese of physicl strength of whet strw under different fertilizer mngement scenrios for sites nd smpling periods in our study my be ttributed to rndomly testing internodes. Future work could eliminte this rndom vrible by consistently selecting prticulr internode for physicl testing. Moisture content of the whet strw specimens t shering test could lso ffect the physicl strength of those strws. Nzri Gledr et l. (2008) mesured the engineering properties of lflf stems under different moisture contents nd found positive reltionship between moisture content nd τ! nd energy. Tvkoli et l. (2009) reported similr finding fter testing the physicl prmeters of brley strw. In our study, whet strw smples were oven dried t 56 for 72 h. After moving the smples from oven to testing lbortory, they were stored in crdbord box in the lbortory where the temperture nd moisture were not precisely controlled. However, lbortory thermostt ws set to 20 nd humidity ws not controlled. Shering test ws operted for two weeks for smples from ech site during ech smpling period. Therefore, the whet strw moisture content could grdully increse over the period of time between when it ws removed from the oven nd when it ws shered, which could cuse inconsistent physicl strength results. 95

114 Compred to the control, effects of liquid fertilizer ppliction on the chemicl properties (totl C, N, nd C:N rtio) of whet strw were found one, three, nd three out of the eight smple sets in our study, respectively. Menwhile, significnt effects on sh content were only found one out of eight smple sets. Residue C content is highly ssocited with whet strw decomposition. Annoussmy et l. (2000) reported 50% reduction of cellulose nd 30% reduction of hemicellulose in whet strw fter 25 dys of incubtion. In our study, the only difference between control group nd fertilizer pplied plots in C content ws mesured t Hys in Summer UANlow nd ATSlow showed the potentil bility to speed the decomposition rte by decresing the C concentrtion compred to the control group. However, reduction of C content ws not mesured in smples from high fertilizer ppliction rte tretments t this site. Furthermore, N content ws expected to increse with increse in N fertilizer ppliction rte. This incresing trend ws observed t ll three sites during the first smpling period. Also, the smples from spring-pplied plots generlly hd higher N content thn those from fll-pplied plots. This difference cn be ttributed to the intervl between tretment ppliction time nd smpling time. Shorter intervls my hve less evportion, leching, nd chemicl rection nd results in higher remining N content. However, this phenomenon ws not observed t other smpling periods, so it is not possible to mke conclusion. Commonly, the C:N rtio cn prtilly explin the decomposition rte. Since we ssume tht N content is the limiting fctor for whet strw decomposition, smller C:N rtio is desired if rpid decomposition is the objective. Similr conclusions were drwn by Melchiori et l. (2014). We did mesure smller C:N rtio t Hys nd Grden City, prticulrly for UANhigh nd Mixed tretments. Therefore, lrger N ppliction rtes could decrese C:N rtio, indicting the 96

115 possibility for quicker strw decomposition. However, we did not consistently mesure lower physicl strength of whet strw from high N rte tretments, indicting some other fctors (e.g., whet vriety) my hve ffected the results. Shorter nd stiffer whet vrieties plnted tody hve low digestibility (Cpper et l., 1992; Trvis et l., 1996), which might led to slow nd less response of physicl strength of whet strw to liquid fertilizer ppliction. Furthermore, the influence of N on C minerliztion remins uncler. Contrdictory findings bout N ddition nd consistent effects on C minerliztion hve been reported (Fog, 1988; Green et l., 1995; Morn et l., 2005; Al-Kisi et l., 2013). According to the multiple nd liner regression results (Tble 2.3 nd 2.4), there is generlly negtive pttern of reltionship between physicl nd chemicl prmeters. Negtive reltionships between totl N content nd τ! were mesured t six smpling periods nd dditionlly, two smpling periods showed negtive reltionship between SE nd totl N content. This indictes tht the higher N content of crop residue might hve potentilly dvnced decomposition. However, n opposite result ws found t the Colby site in Fll 2013, which showed positive reltionship between SE nd N content. Berg nd McClugherty (2007) stted tht N might hve negtive effect on the lignin component of crop residue decomposition over time due to the brrier formed by chemicl bonds between lignin nd N during de novo synthesis of lignin. This my explin the opposite findings t Colby in Fll 2013 t which greter N content resulted in less τ!, however, greter SE. Sher stress (τ! ) describes the sher force resistibility t the breking point. Decomposed crop residue usully hs frgile structure. However, the de novo synthesis of lignin cn cuse weker, yet elstic structure due to the chemicl bounds. Since the effects of totl C on physicl prmeters were only observed few 97

116 times nd sh content ws not selected by the multivrite stepwise regression model, we cnnot suggest using totl C nd sh content s indictors to evlute crop residue decomposition. In the liner regression, C:N rtio showed positive reltionship with τ! t five out of eight smpling periods. Menwhile, two smpling periods hve positive reltionship between SE nd C:N rtio. One smpling period hd the opposite result. Wider C:N rtio usully suggests slow decomposition sitution. Bldock (2007) found plnt residues with C:N rtio greter thn 40 hd significntly slower minerliztion process thn residue with C:N rtio less thn 40. The opposite result ws mesured t Colby in Fll 2013 gin. Setting drying temperture t 56 my result in further decomposition of whet strw. Cone et l. (1996) reported tht different chemicl compound contents nd physicl properties of grss nd mize during degrdtion could be ttributed to temperture choice. Therefore, multiple drying tempertures could be evluted in the future studies. A chmber study tht would control the environmentl fctors (i.e., soil moisture content, temperture, nd wind) nd precisely pply fertilizer to crop residue ccordingly would be n excellent follow-up study. Conclusions Physicl prmeters (i.e., boveground biomss, τ!, nd SE) nd chemicl prmeters (i.e., totl C nd N content, C:N rtio, nd sh content) of whet strw were evluted to ssess the impcts of fertilizer ppliction rtes nd timing on its decomposition. Overll, there were no consistent results to revel ny predictble reltionship between fertilizer ppliction rtes nd whet strw decomposition. However, smller remining biomss, less SE nd τ!, nd nrrower C:N rtio were mesured t different sites during different smpling periods indicting some, lbeit inconsistent, potentil of pplying fertilizer to hsten whet strw decomposition. Longer 98

117 ppliction periods tended to reduce the whet strw physicl strength t some sites (Summer 2012 nd Fll 2013 t Hys). Multivrite nd liner regression nlysis suggested tht N nd C:N rtio my be prcticl indictors to ssess crop residue decomposition. 99

118 Figures nd tbles Figure 2.1 Design of the sher box nd photogrph of the mnufctured sher box. Unit: cm Chmber Top View Chmber Front View Blde Front View Blde Side View 100

119 Figure 2.2 Testing whet strw physicl strength using sher box ttched with lod cell Instron MN 44 (Instron, Norwood, MA) tht is connected to computer. 101

120 Figure 2.3 Sher force long blde movement recorded by computer with different colors showing different shering stges. 102

121 Figure 2.4 Imge of cross section of whet strw t the breking point under microscope (left) nd being nlyzed by the imge nlysis softwre pckge SigmScn 5 (Systt Softwre Inc.) (right). 103