Evaluation of residue management practices effects on corn productivity, soil quality, and greenhouse gas emissions

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1 Grute Theses n Disserttions Iow Stte University Cpstones, Theses n Disserttions 2013 Evlution of resiue mngement prties effets on orn proutivity, soil qulity, n greenhouse gs emissions Jose Germn Guzmn Iow Stte University Follow this n itionl works t: Prt of the Soil Siene Commons Reommene Cittion Guzmn, Jose Germn, "Evlution of resiue mngement prties effets on orn proutivity, soil qulity, n greenhouse gs emissions" (2013). Grute Theses n Disserttions This Disserttion is rought to you for free n open ess y the Iow Stte University Cpstones, Theses n Disserttions t Iow Stte University Digitl Repository. It hs een epte for inlusion in Grute Theses n Disserttions y n uthorize ministrtor of Iow Stte University Digitl Repository. For more informtion, plese ontt igirep@istte.eu.

2 Evlution of resiue mngement prties effets on orn proutivity, soil qulity, n greenhouse gs emissions y Jose Germn Guzmn A isserttion sumitte to the grute fulty in prtil fulfillment of the requirements for the egree of DOCTOR OF PHILOSOPHY Mjor: Soil Siene (Soil Mngement) Progrm of Stuy Committee: Mhi M. Al-Kisi, Mjor Professor John E. Swyer Antonio P. Mllrino Tim B. Prkin Fernno E. Miguez Iow Stte University Ames, Iow 2013 Copyright Jose Germn Guzmn, All rights reserve.

3 ii To my prents, Germn n Luz Mri Guzmn, for their ptiene, srifie, n onfiene.

4 iii TABLE OF CONTENTS LIST OF FIGURES... iv LIST OF TABLES... vi LIST OF ABBREVIATIONS... viii ACKNOWLEDGEMENTS... ix ABSTRACT... x CHAPTER 1: GENERAL INTRODUCTION... 1 CHAPTER 2: RESIDUE MANAGEMENT EFFECTS ON CORN PRODUCTIVITY, SOIL CARBON, AND SOIL PHYSICAL PROPERTIES Astrt n Introution... 6 Mterils n Methos... 9 Results n Disussion Conlusions Referenes CHAPTER 3: RESIDUE MANAGEMENT EFFECTS ON SOIL TEMPERATURE, WATER CONTENT, AND GREENHOUSE GAS EMISSIONS Astrt n Introution Mterils n Methos Results n Disussion Conlusions Referenes CHAPTER 4: SOIL CARBON BUDGET UNDER DIFFERENT RESIDUE REMOVAL MANAGEMENT SYSTEMS Astrt n Introution Mterils n Methos Results n Disussion Conlusions Referenes CHAPTER 5: GENERAL CONCLUSIONS

5 LIST OF FIGURES Figure 2.1. Monthly ir temperture n rinfll in the AC site Figure 2.2. Monthly ir temperture n rinfll in the ASW site Figure 2.3. Resiue removl effets on orn grin yiel y mngement prtie iv in the AC site Figure 2.4. Resiue removl effets on orn grin yiel y mngement prtie in the ASW site Figure 2.5. Resiue removl effets on soil temperture n wter ontent y tillge n yer in the AC site Figure 2.6. Resiue removl effets on soil temperture n wter ontent y tillge n yer in the ASW site Figure 2.7. Miroil iomss ron fter three yers of resiue removl y tillge, n site Figure 2.8. Unjuste n juste soil penetrtion resistne fter three yers of resiue removl n tillge in the AC site Figure 2.9. Unjuste n juste soil penetrtion resistne fter three yers of resiue removl n tillge in the AC site Figure Wter stle ggregte istriution s ffete y mngement prtie in the AC site Figure Wter stle ggregte istriution s ffete y mngement prtie in the ASW site Figure Aggregte men weight imeter s ffete y mngement prtie in the AC site Figure Aggregte men weight imeter s ffete y mngement prtie in the ASW site Figure Wter infiltrtion rtes fitte y Horton s moel y mngement prtie in the AC site Figure Wter infiltrtion rtes fitte y Horton s moel y mngement prtie in the ASW site Figure 3.1. Soil temperture, wter ontent n minerl nitrogen y mngement prtie in 2009 t AC site

6 v Figure 3.2. Soil temperture, wter ontent n minerl nitrogen y mngement prtie in 2010 t AC site Figure 3.3. Soil temperture, wter ontent n minerl nitrogen y mngement prtie in 2010 t ASW site Figure 3.4. Soil temperture, n wter ontent y mngement prtie in 2011 t AC site Figure 3.5. Soil temperture, n wter ontent y mngement prtie in 2011 t ASW site Figure 3.6. Soil surfe CO 2 emissions y mngement prtie in ll yers t AC site Figure 3.7. Soil surfe CO 2 emissions y mngement prtie in ll yers t ASW site Figure 3.8. Soil surfe N 2 O emissions y mngement prtie in 2009 n 2010 t AC site Figure 4.1. Miroil n root respirtion, soil temperture n wter ontent y mngement prtie in 2010 t AC site Figure 4.2. Miroil n root respirtion, soil temperture n wter ontent y mngement prtie in 2011 t AC site Figure 4.3. Miroil n root respirtion, soil temperture n wter ontent y mngement prtie in 2010 t ASW site Figure 4.4. Miroil n root respirtion, soil temperture n wter ontent y mngement prtie in 2011 t ASW site Figure 4.5. Cumultive miroil respirtion in the totl n top 7.5 m soil epth y mngement prtie in 2010 n 2011 t AC site Figure 4.6. Cumultive miroil respirtion in the totl n top 7.5 m soil epth y mngement prtie in 2010 n 2011 t ASW site Figure 4.7. Soil ron uget in the totl n top 7.5 m soil epth y mngement prtie in 2010 n 2011 t AC site Figure 4.8. Soil ron uget in the totl n top 7.5 m soil epth y mngement prtie in 2010 n 2011 t ASW site

7 vi LIST OF TABLES Tle 2.1. Soil ulk ensity, ron, n nitrogen t the top 15 m soil epth fter three yers of resiue removl in the AC site Tle 2.2. Soil ulk ensity, ron, n nitrogen in the 15 to 30 m soil epth fter three yers of resiue removl in the AC site Tle 2.3. Soil ulk ensity, ron, n nitrogen in the 30 to 45 m soil epth fter three yers of resiue removl in the AC site Tle 2.4. Soil ulk ensity, ron, n nitrogen in the 45 to 60 m soil epth fter three yers of resiue removl in the AC site Tle 2.5. Soil ulk ensity, ron, n nitrogen in the 0 to 60 m soil epth fter three yers of resiue removl in the AC site Tle 2.6. Soil ulk ensity, ron, n nitrogen t the top 15 m soil epth fter three yers of resiue removl in the ASW site Tle 2.7. Soil ulk ensity, ron, n nitrogen in the 15 to 30 m soil epth fter three yers of resiue removl in the ASW site Tle 2.8. Soil ulk ensity, ron, n nitrogen in the 30 to 45 m soil epth fter three yers of resiue removl in the ASW site Tle 2.9. Soil ulk ensity, ron, n nitrogen in the 45 to 60 m soil epth fter three yers of resiue removl in the ASW site Tle Soil ulk ensity, ron, n nitrogen in the 0 to 60 m soil epth fter three yers of resiue removl in the ASW site Tle Correltions etween selete soil properties fter three yers of resiue removl in the AC site Tle Correltions etween selete soil properties fter three yers of resiue removl in the ASW site Tle 3.1. Cumultive soil surfe CO 2 emissions y mngement prtie in the AC n ASW sites Tle 3.2. Cumultive soil surfe N 2 O emissions y mngement prtie in the AC site Tle 3.3. Soil surfe CO 2 emissions s preite y soil temperture n wter ontent

8 vii Tle 3.4. Soil surfe N 2 O emissions s preite y soil temperture n wter ontent n minerl nitrogen Tle 3.5. Soil surfe N 2 O emissions s preite y soil temperture n wter ontent n minerl nitrogen Tle 4.1. Aove- n elowgroun iomss y mngement prtie in AC site in 2009 n Tle 4.2. Aove- n elowgroun iomss y mngement prtie in ASW site in 2009 n Tle 4.3. Contriution of miroil respirtion to totl soil surfe CO 2 emissions within n in etween rows y mngement prtie Tle 4.4. Contriution of CO 2 from the top 7.5 m to totl soil surfe CO 2 emissions y mngement prtie

9 viii LIST OF ABBREVIATIONS AC, Ames Centrl site ASW, Armstrong Southwest site A-SPR, juste soil penetrtion resistne ρ, ulk ensity C, ron CT, onventionl tillge CO 2, ron ioxie DAP, ys fter plnting DOY, y of the yer ESM, equivlent soil mss F, finl infiltrtion pity GWP, glol wrming potentil GHG, greenhouse gs I r, wter infiltrtion rte MWD, ggregte men weight imeter CH 4, methne MBC, miroil iomss ron R h, miroil respirtion N, nitrogen N 2 O, nitrous oxie NT, no-tillge R r, root respirtion SOC, soil orgni ron SPR, soil penetrtion resistne Stemp, soil temperture T CO2, totl soil surfe ron ioxie emission TN, soil totl nitrogen WSA, wter stle ggregtes θv, wter ontent

10 ix ACKNOWLEDGMENTS First, I woul like to thnk my ommittee Dr. John Swyer, Dr. Antonio Mllrino, Dr. Tim Prkin, n Dr. Fernno Miguez for tking the time to work with me uring this enevor. I woul lso like to express my eepest grtitue to my mjor professor, Dr. Mhi Al-Kisi, who provie the inspirtion n guine uring the reserh n preprtion for this oument. My ppreition lso goes to the frm mngers in the Ames n Armstrong reserh frms, for their ssistne in estlishment of fiel plots. Speil thnks re ue to Crlos Tenes n Chris Pelzer, for their tireless efforts uring fiel n l work. Without them, this reserh woul hve een most iffiult. To my motivtion to suee, my rother, Omr, n sister, Nny, for their enourgement they hve given me. Most importntly, my prents who estowe upon me soli work ethi, without whih I woul not hve een le to suee in higher eution. Thnk you for your ptiene, srifie, n onfiene you hve given.

11 x ABSTRACT Crop resiue is n importnt omponent of the soil orgni ron (SOC) uget n evelopment of soil qulity inies. However, rop resiue in reent yers hs een onsiere s nother potentil feestok soure for ethnol proution in ition to or lterntive to grin. The urrent emphsis on using rop resiue s feestok for future ethnol proution presents soil n environmentl hllenge tht nees to e resse. Aitionlly, there hve een few stuies tht exmine greenhouse gs (GHG) emissions from griulture soils uner ifferent resiue removl rtes, vrious N rtes, n tillge prties n their intertions effets on soil C ynmis n GHG emissions. The ojetive of this stuy ws to exmine potentil hnges in rop proutivity, soil C sequestrtion, n GHG emissions uner no-till (NT) n (CT) n N fertiliztion rtes of 0, 170, n 280 kg N h -1 with vrile rtes of resiue removl (0, 50, n 100%). Fiel stuies were estlishe in fll of 2008 on two sites, poorly-rine soil t the Iow Stte University Agronomy Reserh Frm (Centrl, Iow, AC) n well-rine soil t the Armstrong Reserh n Demonstrtion Frm (Southwest, Iow, ASW) in ontinuous orn. After three yers of resiue removl, SOC, TN, miroil iomss-ron (MBC), ulk ensity (ρ ), soil penetrtion resistne (SPR), wter stle ggregtes (WSA), n infiltrtion (I r ) were mesure. After every hrvest, rop mesurements inlue orn grin yiel, ove-groun iomss, n root-iomss. Weekly mesurements of soil surfe CO 2, n N 2 O emissions ouple with soil moisture n tempertures were ollete uring the growing seson. Aitionlly soil C ugets were lulte to provie insights on whether these mngement prties resulte in net gins or losses of soil C. After three yers of resiue removl, uner ifferent mngement prties, the finings of this stuy suggest tht portion of the orn resiue tht is left on the soil surfe fter hrvest

12 xi n e remove, with no negtive impts in the short term yiels in the AC n ASW sites. However, inreses of ρ, n SPR were oserve with 50 n 100% resiue removl regrless of tillge n N fertiliztion rte. Furthermore, ereses in SOC, MBC, WSA, n I r were oserve with resiue removl, lthough hnges vrie with soil type n mngement prties. Mngement prties tht reue soil orgni minerliztion vi reuing soil temperture n oxition suh s in NT, is vile strtegi mens for mitigtion CO 2 -C emissions. Although N 2 O-N emissions ontriutions to glol wrming potentil (GWP) were onsierly lower thn CO 2 -C emissions, ifferenes in N fertiliztion rtes i hve signifint impt on GWP in this stuy. Results from the soil C ugets suggest tht uner mngement prties of CT n N fertiliztion rtes of 170 kg N h -1 in ontinuous orn, net soil C hnge ws pproximtely zero when no resiue ws remove for these sites n yers. With no other hnges in the fore mention mngement prties, ny removl of soil surfe resiue resulte in net soil C losses. Inresing N fertiliztion rtes from 170 to 280 kg N h -1, resulte in higher C inputs from ovegroun n root iomss, n C losses vi R h not eing signifintly ifferent when ompre to 170 kg N h -1 fertiliztion rte. In 2010 when orn growth ws not limite to lk of soil moisture, pproximtely 35 n 30% of the resiue oul e sustinly remove (i.e. net inrese or no net loss of soil C) in the AC n ASW sites, respetively. In 2011, rier soil onitions resulte in pproximtely 2 n 49% of the resiue oul e sustinly remove in the AC n ASW sites, respetively. In generl, onverting from CT to NT n inrese rtes of N fertiliztion i offset some of the negtive impts of resiue removl, lthough potentil losses of SOC n eteriortion of soil physil properties were still oserve fter three yers of resiue removl.

13 1 CHAPTER 1 Generl Introution Corn (Ze mys L.) resiue left on the surfe fter hrvest is potentil feestok soure for ioethnol proution whih n ontriute to the reution of fossil fuel use n net greenhouse gs emissions (Wilhelm et l., 2004; Grhm et l., 2007). Although, it is urrently more expensive to proue ethnol from lignoellulosis thn from strhes, it is projete tht improvements in tehnology n sle of proution will improve these osts (Foust et l., 2009). It is prole tht lignoellulosi ethnol proution will eome vile option n oul rete n nnul mrket for rop resiue from pproximtely 143 million tons to million tons (Downing et l., 2011). The removl of rop resiue, however, my require frmers to hnge their urrent tillge n fertiliztion prties to prevent potentil soil erosion. Crop resiues ply signifint role in improving soil physil n hemil properties tht re essentil in ontrolling win n wter erosion, whih ultimtely reue seiment n other ontminnt trnsport to wter oies (Krlen et l., 1994). Crop resiues re lso ritil for replenishing SOC (Al-Kisi n Yin, 2005). In ition, griulture ounts for 10 to 20% of the totl nthropogeni GHG emissions, ut is responsile for 58% of the totl nthropogeni N 2 O emissions (Smith et l., 2007). Sine urrent griulture prties re responsile for lrge proportion of N 2 O emissions, hnges in mngement prties n hve signifint hnges in N 2 O n CO 2 emissions levels. More reserh is neee to further unerstn the key soures n mehnisms responsile for generting N 2 O n CO 2 emissions in griulture systems for the evelopment of future mitigtion strtegies.

14 2 One suh strtegy is the use of griulture ln for the mitigtion of elevte tmospheri CO 2 levels through the sequestrtion of SOC. Soils ontin the lrgest tive terrestril C pool on erth (3,150 Pg C), n ontriute 10 times more CO 2 (75 Pg C yr -1 from soil respirtion) to the tmosphere thn fossil fuel omustion (Pustin et l., 2002). The risk of glol wrming n interest in option of the Kyoto Protool hs inrese the ttention of the sientifi ommunity on SOC sequestrtion in terrestril eosystems. However, preise mesurement n verifition of the mount of C sequestere in the soil hve proven to e iffiult. The usge of SOC eplete ln s sink for some of the exess CO 2 ppers to e prtil n ost effetive metho of reuing tmospheri CO 2 levels (Post n Kwon, 2000). The si thought ehin reuing tmospheri CO 2 emissions through SOC sequestrtion y hnges in ln use relies on the restortion of originl ntive C levels. The mgnitue of SOC storge epens on rnge of ftors suh s; soil type, ln use, nnul input of C from plnts, plnt type, n the severity of egrtion (Johnson et l., 2007). Currently, there re few stuies tht hve evlute the intertion effets of resiue removl rtes uner ifferent mngement prties on potentil hnges in rop yiels, SOC, n soil qulity for onlusive estimte on how muh rop resiue n sustinly e remove in system (Linen et l., 2000; Wilhelm et l., 2004; Doln et l., 2006). Aitionlly, sustinility of rop resiue removl will lso epen hevily on the ropping system (Dorn et l., 1984), limte n soil type (Mu et l., 2008) whih nee to e speifie regionlly. We hypothesize tht potentil losses in rop proutivity, SOC, n soil qulity in generl ue to resiue removl, oul e reue y ltering mngement prties tht hve lower intensity of tillge n greter N fertiliztion rtes. The ojetives of this stuy were to exmine how tillge, N fertiliztion rtes, resiue removl, n their intertions ffet: (i) rop proutivity, SOC,

15 3 soil physil properties, n (ii) GHG emissions, n (iii) n soil C ugets fter three yers of resiue removl in Centrl n Southwest Iow. Disserttion Orgniztion This isserttion is orgnize into five hpters, eh ressing speifi spet on the effets of resiue removl on soil n ir qulity. The first hpter is generl introution tht outlines the relevne of this stuy. The seon hpter exmines the impts of resiue removl on rop proutivity, SOC, n soil physil properties. The thir hpter fouses on GHG emissions s ffete y soil temperture n wter ontent. The fourth hpter fouses on soil C ugets n etermining how muh resiue n sustinly e remove. Chpter five summrizes onlusions of the reserh projet finings. Evlution of these prmeters will help in unerstning intertion effets of resiue removl rtes uner ifferent mngement prties on potentil hnges in rop yiels, SOC, n soil physil qulity. Referenes Al-Kisi, M.M., n Yin, X., Tillge n rop resiue effets on soil ron n ron ioxie emission in orn-soyen rottions. J. Environ. Qul. 34: Doln, M.S., Clpp, C.E., Allmrs, R.R., Bker, J.M., n Molin, J.A.E., Soil orgni nitrogen in Minnesot soil s relte to tillge, resiue, n nitrogen mngement. Soil Till. Res. 89: Dorn, J.W., Wilhelm, W.W., n Power, J.F., Crop resiue removl n soil proutivity with no-till orn, sorghum, n soy-en. Soil Si. So. Am. J. 48: Downing, M., Eton, L.M., Grhm, R.L., Lngholtz, M.H., Perlk, R.D., Turhollow, Jr. A.F., Stokes, B., n Brnt, C.C., U.S. illion-ton upte: iomss supply for ioenergy n ioprouts inustry. pp. Meium: ED.

16 4 Foust, T.D., Aen, A., Dutt A., n Phillips, S., An eonomi n environmentl omprison of iohemil n thermohemil lignoellulosi ethnol onversion proesses. Cellulose 16: Grhm, R.L., Nelson, R., Sheehn, J., Perlk, R.D., n Wright, L.L., Current n potentil U.S. orn stover supplies. Agron. J. 99: Johnson, J.M.-F., Frnzlueers, A.J., Weyers, S.L., n Reiosky, D.C., Agriulturl opportunities to mitigte greenhouse gs emissions. Environ. Pollu. 150: Krlen, D.L., Wollenhupt, N.C., Erh, D.C., Berry, E.C., Swn, J.B., Esh, N.S., n Jorhl, J.L., Crop resiue effets on soil qulity following 10-yers of no-till orn. Soil Till. Res. 31: Linen, D.R., Clpp, C.E., n Dowy, R.H., Long-term orn grin n stover yiels s funtion of tillge n resiue removl in est entrl Minnesot. Soil Till. Res. 56: Mu, Z.J., Kimur, S.D., Tom, Y., n Htno, R., Evlution of soil ron sequestrtion uner ifferent upln ropping systems in entrl Hokkio, Jpn. Soil Si. Plnt Nutr. 54: Pustin, K., Brenner, J., Killin, K., Cipr, J., Willims, S., Elliott, E.T., Eve, M.D., Kutz, T., n Bluhm, G., Stte-level nlyses of C sequestrtion in griulturl soils. In: R. Ll et l. (ED.) Agriulturl prties n poliies for ron sequestrtion in soil. CRC Press, Bo Rton, FL. pp Post, W.M., n Kwon, K.C., Soil ron sequestrtion n ln-use hnge: Proesses n potentil. Glo. Chnge Biol. 6: Smith, P., Mrtino, D., Ci, Z., Gwry, D., Jnzen, H., Kumr, P., MCrl, B., Ogle, S.,

17 5 O Mr, F., Rie, C., Sholes, B., n Sirotenko, O., et l., Poliy n tehnologil onstrints to implementtion of greenhouse gs mitigtion options in griulture. Agri. Eosyst. Environ. 118: Wilhelm, W.W., Johnson, J.M.F., Htfiel, J.L., Voorhee, W.B. n Linen, D.R., Crop n soil proutivity response to orn removl: A literture review. Agron. J. 96: 1-17.

18 6 CHAPTER 2 RESIDUE MANAGEMENT EFFECTS ON CORN PRODUCTIVITY, SOIL CARBON, AND SOIL PHYSICAL PROPERTIES Astrt Crop resiue left on the surfe fter hrvest is potentil feestok soure for ioethnol proution tht my llevite some of the Unite Sttes epenene on foreign fuel n net greenhouse gs emissions. The removl of rop resiue, however, my require frmers to hnge their urrent tillge n fertiliztion prties to prevent potentil soil erosion n epletion in soil nutrients. The ojetives of this stuy were to exmine how tillge, N fertiliztion rtes, resiue removl, n their intertions ffet rop proutivity, SOC, n selete soil physil properties fter three yers of resiue removl in Centrl n Southwest Iow. The finings of this stuy suggest tht portion of the orn resiue tht is left on the soil surfe fter hrvest n e remove, with no negtive impts on short term yiels in two sites in Centrl n Southwest Iow. However, signifint ereses in SOC sequestrtion rtes, MBC, ρ, A-SPR, MWD, n I r were oserve, ut vrie with soil type n mngement prtie. In poorlyrine soils t the AC site, signifint inreses in SOC ontent were oserve when onverting from CT to NT systems, even when 50 n 100% of the rop resiue ws remove uring three yers of this stuy. Averge SOC sequestrtion rtes of 2.05 Mg C h -1 yr -1 were oserve in NT, 78% greter tht of CT tretments for the entire soil profile (0 to 60 m). However, signifint ereses in MBC, ρ, A-SPR, MWD, n I r were oserve regrless of tillge n N fertiliztion rte in the top 15 m soil epth when 50 n 100% of resiue ws remove. In the well-rine soils t the ASW site, SOC sequestrtion rtes were in generl negtive regrless of tillge n resiue removl n N fertiliztion rte t the 0 to 60 m soil profile. SOC ontent

19 7 losses were signifintly lower uner CT tretments t Mg C h -1 yr -1, ompre to NT tretments t Mg C h -1 yr -1. Negtive impts of resiue removl on soil physil properties were more severe in the ASW site ompre to the AC site in generl. These results show tht resiue removl effets on rop proutivity, SOC, n soil physil properties vry y mngement prties n soil type n re site speifi. Introution Corn (Ze mys L.) resiue left on the surfe fter hrvest is potentil feestok soure for ioethnol proution whih n ontriute to the reution of fossil fuel use n net greenhouse gs emissions (Wilhelm et l., 2004; Grhm et l., 2007). Although, it is urrently more expensive to proue ethnol from lignoellulosis thn from strhes, it is projete tht improvements in tehnology n sle of proution will improve these osts (Foust et l., 2009). It is prole tht lignoellulosi ethnol proution will eome vile option n oul rete n nnul mrket for rop resiue from pproximtely 143 million tons to million tons (Downing et l., 2011). Although foreseele ereses in soil orgni ron (SOC), soil qulity, n rop proutivity with exessive rop resiue removl re expete in the short (Blno-Cnqui n Ll, 2007) n long term (Linen et l., 2000; Wilts et l., 2004); it is unertin if in, ooler regions in the Corn Belt where soils re inherently fine texture with poor ringe, onitions re suitle for prtil removl of resiue. Crop proutivity in these soils re ommonly reue y ooler soil tempertures in the spring, whih often les to reue plnt emergene, N minerliztion, n rop growth (Wolfe n Ekert, 1999; Al-Kisi n Kww-Mensh, 2007). Consequently, stuies hve shown tht removing surfe rop resiues le to soil tempertures wrming up fster in the spring, thus inresing rop yiels in soils whih re

20 8 inhiite y ol n wet onitions (Horton et l., 1994). However, this short term gin in yiels re just one omponent tht nees to e resse when etermining how muh resiue n e remove without negtively impting SOC, soil physil n hemil properties, n long-term yiel potentil (Wilhelm et l., 2004; Ll, 2009). The removl of rop resiue, however, my require frmers to hnge their urrent tillge n fertiliztion prties to prevent potentil soil erosion n epletion in soil nutrients. It is well oumente through reserh over the pst mny ees tht rop resiues re ritil for proteting the soil surfe from win n wter erosion n improving soil physil properties (Linstrom, 1986). Crop resiues lso replenish n inrese soil orgni mtter, whih is ritil for mintining soil nutrients suh s SOC, N, P, n K (Krlen, et l., 1994). Aitionlly, mngement prties tht inrese SOC hve een shown to improve soil struture y enhning ggregte stility, n eresing ρ whih result in greter wter infiltrtion rtes (Blno-Cnqui n Ll, 2007; Guzmn n Al-Kisi, 2011). Some stuies hve suggeste tht in orer to meet the emns of the ioethnol inustry, frmers will nee to inresingly pt to no-till (NT) prties in orer to offset potentil SOC losses from rop resiue removl (Kim n Dle, 2004). This is ue to tillge effets generlly inresing soil C losses y: inuing the vilility of oxygen n oxition of SOC shortly fter tillge (Reiosky, 1997; Al-Kisi n Yin, 2005), n estrution of soil ggregtes tht physilly protets SOC from miroil tivities (Six et l., 2000). It hs lso een suggeste tht inreses in N fertiliztion rtes my lso further i in soil C sequestrtion (Wilts et l., 2004; Vlekn King, 2011), ue to inreses in ovegroun iomss n espeilly root iomss, whih n ontriute to more stle SOC erive C thn o ovegroun resiue (Rsse et l., 2005).

21 9 Currently, there re few stuies tht hve evlute the intertion effets of resiue removl rtes uner ifferent mngement prties on potentil hnges in rop yiels, SOC, n soil qulity for onlusive estimte on how muh rop resiue n sustinly e remove in system (Linen et l., 2000; Wilhelm et l., 2004; Doln et l., 2006). Aitionlly, sustinility of rop resiue removl will lso epen hevily on the ropping system (Dorn et l., 1984), limte n soil type (Mu et l., 2008) whih nee to e speifie regionlly. We hypothesize tht potentil losses in SOC n soil qulity in generl ue to resiue removl, oul e reue y ltering mngement prties tht hve lower intensity of tillge n greter N fertiliztion rtes. The ojetives of this stuy were to exmine how tillge, N fertiliztion rtes, resiue removl, n their intertions ffet rop proutivity, SOC, n selete soil physil properties fter three yers of resiue removl in Centrl n Southwest Iow. Mterils n Methos Experimentl sites n tretments A stuy ws estlishe in fll of 2008 on Niollet (fine-lomy, mixe supertive, mesi Aqui Hpluoll) n Cnisteo ly lom (Fine-lomy, mixe, supertive, lreous, mesi Typi Enoquolls) soil ssoition t Iow Stte University Agronomy Reserh Frm (AC) in Centrl, Iow (42.4 o 'N; 95.5 o 'W) n Mrshll silty ly lom (Fine-silty, mixe, supertive, mesi Typi Hpluolls) soil ssoition t Armstrong Reserh n Demonstrtion Frm (ASW) Southwest, Iow (41.3 o 'N; 95.1 o 'W) in ontinuous orn. The men ir temperture n nnul preipittion t the AC site re 8.7 o C n 975 mm, respetively (t from 1982 to 2011) (Fig. 2.1). In the ASW site, men ir temperture n nnul preipittion re 9.5 o C n 909 mm, respetively (t from 1982 to 2011) (Fig. 2.2). Both sites were previously in orn-

22 10 soyen [Glyine mx (L.) Merr.] rottion uner onventionl tillge (CT, hisel plow in fll n hisel plus isk in the spring). Soure of N ws liqui ure-mmonium nitrte 32% N (UAN) whih ws sie-resse injete in My fter plnting using gronomi rtes of 170 kg N h -1 uring the orn phse (Blkmer et l., 1997). Phosphorus n potssium fertiliztion pplition ws one perioilly to mintin optimum soil onentrtions so s not to restrit orn growth uring the length of this stuy. Three tretments were pplie in 2008 to 2011 for oth sites in rnomize, ompletelok esign with split-split rrngement n three replitions. The min plot tretment ws tillge prtie (NT n CT), whih ws split into three ifferent resiue removl rtes (0, 50, n 100%) whih ws further split into three N fertiliztion rtes of 0, 170, n 280 kg N h -1. As one previously from pst mngement, soure of N ws 32% liqui UAN whih ws injete sie-resse in My fter plnting. Shortly fter orn hrvest, esire rtes of resiue removl were omplishe y justing own-pressure on rking pprtus efore ling of resiue. For 100% removl, orn stlks n leves were first mowe then rke ler own (very high own-pressure) for resiue to e ollete y ler. After ling, plots were hn rke to hieve nerly 100% removl. For 50% removl, resiue ws not mowe n erese ownpressure of the rke pprtus ws set so s to leve pproximtely 50% of the soil surfe overe fter ling. Atul removl of resiue y mss vrie y N rte, tillge, site, n yer rnging from 30-50% n 73-91% for 50 n 100% resiue removl tretments, respetively. Both sites were plnte using 111 y mturity orn vriety (P33W84) t seeing ensity of 79,000 sees h -1.

23 11 Soil orgni ron, totl nitrogen, n ulk ensity Soil smples were ollete fter hrvest in mi-otoer, prior to estlishment of tretments in 2008 n three yers fterwrs in 2011, to mesure ny hnges in SOC, n totl nitrogen (TN). Twelve 1.7 m imeter soil ores were ollete from epths of 0 to 15, 15 to 30, 30 to 45, n 45 to 60 m in eh tretment plot. Soil ores for eh epth were omine into single homogeneous smple. Soil smples were 2 mm sieve n then ir rie efore eing nlyze. The TC n TN were etermine y ry omustion using LECO CN nlyzer (LECO Corportion, St. Joseph, Mihign). A seprte ronte nlysis using moifie pressure limeter metho ws use to estimte inorgni C, whih ws sutrte from TC results to en up with totl SOC (Sherro et l., 2002). Conurrently with TC n TN soil smples were eing tken, three ulk ensity (ρ ) smples were ollete from eh tretment plot, using 1.7 m imeter soil proe. Soil ores were tken t the sme soil epths s SOC smples n were then oven rie t 105 C for 24 hours n weighe. Bulk ensity (Mg m 3 ) ws lulte s the rie soil mss ivie y the soil ore volume. The SOC n TN onentrtions (mg g 1 ry soil) tht were mesure in 2008 were multiplie y men ρ vlues n soil epth thikness to onvert SOC n TN onentrtions to mss per re sis (Mg h 1 ) for ll tretment plots y soil epth. For smples ollete in 2011, SOC n TN ontent ws lulte similr to initil smples, lthough onentrtions of SOC n TN for eh soil profile epth were juste for gins or losses in soil mss, ue to hnges in ρ, for the originl or equivlent soil mss (ESM) in 2008 to etermine hnges in SOC n TN stoks (Lee et l., 2009).

24 12 Miroil iomss ron Twelve soil ore smples were ollete in eh tretment plot using 1.7 m imeter proe to 15 m epth shortly fter hrvest in mi-otoer in Miroil iomss ron (MBC) ws etermine y performing fumigtion extrtion (Horwth n Pul 1994). Soil smples were fumigte with ethnol-free hloroform (CHCl 3 ) for 24 hours in vuum esitor. The soil smples were extrte for 30 minutes with 100 ml of 0.5 M potssium sulfte (K 2 SO 4 ) n then were filtere through Whtmn No. 42 filter pper. A similr extrtion ws performe on the non-fumigte soil smples. The extrtnt (K 2 SO 4 ) lone ws lso filtere to etermine the kgroun level of C in the filter pper n extrtnt. Cron reovere in the extrt ws mesure with n ElementrliquiTOC ron nlyzer (Ameris In., Mt. Lurel, New Jersey). The MBC ws lulte on n oven ry weight sis. Soil penetrtion resistne Soil penetrtion resistne (SPR) ws etermine using Rimik CP-20 penetrometer (Soil Mesurement Systems, Tuson, AZ) shortly fter hrvest in mi-otoer in The penetrometer use 30 o one with se 1.27 m in imeter. The trgete insertion spee ws 1.3 m min 1, with rnge of 0.1 to 2 m min 1. In 2011 shortly fter hrvest, three insertion points per tretment plot were reore t 2.5 m soil epth inrements own to 60 m. Insertion points were lote etween orn rows, in the row, n etween the fore mentione points. The SPR mesurements were juste (A-SPR) to ommon vlue of soil grvimetri wter ontent of 0.27 g g -1, to reue onfouning effets of soil wter ontent t time of mesurements y: [1] where SPR is in MP,, W is wter ontent on ry weight sis in g g -1, n n re empiril prmeters tht were lulte (Bussher et l., 1997). In the AC site, lulte n

25 13 prmeters were 5.67 n In the ASW site, lulte n prmeters were n Corretions of SPR for ifferenes of wter ontent were se on first Tylor series expnsion: [2] where A-SPR is in MP, SPR o ws the originl SPR, W is the ommon wter ontent to whih the SPR is eing orrete, W o is the originl wter ontent, n C/W ws the first erivtive of eqution one. At time of SPR mesurements, verge soil grvimetri wter ontent throughout the whole soil profile epth t oth sites ws 0.27 g g -1, whih ws use for the W vlue. Wter stle ggregte istriution n men weight imeter Soil smples for wter stle ggregtes (WSA) were tken using 10.5 m imeter golf ourse hole utter to soil epth of 15 m etween orn rows n in the row for eh tretment plot. Smples were then gently psse through 8 mm sieve to remove ny unesirle plnt resiue n roks. Soil smples were then ir rie n store for nlysis. The WSA size istriutions were etermine following the proeure from Kemper n Rosenu (1986) with some moifitions. A soil smple of 100 g ws use for wet sieving for 5 min in eionize wter t 21 C. By lowering n then rising the sieves with stroke length of 20 mm n frequeny of 90 strokes min 1, using ustom me sieving mhine where 20 m imeter sieves oul fit. Seven ggregte size frtions were ollete, >4 mm, 2 to 4 mm, 1 to 2 mm, 0.5 to 1 mm, 0.25 to 0.5 mm, n to 0.25 mm. For the remining smple tht psse through the lst sieve, mm, it ws onsiere <0.053 mm. Eh soil smple ws first miste with spry ottle n then sumerge in wter in the top sieve for t lest 5 min efore wet sieving egn to slke off ir rie soil. In ition, this pre-wetting reue uilup of ir

26 14 pressure in pores resulting in less ir esping with miniml ggregte isruption. Following wet sieving, soil smple of eh ggregte frtion ws trnsferre y wshing it into tus n then oven rie t 65 C until ll wter ws evporte. Dry weight of eh frtion size ws reore. In ition, WSA ry weights were then juste to soil moisture orretions from ir-rie susmples of WSA. The ggregte stility for eh soil smple ws then expresse y men weight imeter (MWD) (Youker n Mguiness 1957): [3] where MWD is the men weight imeter in mm, xr i is the men imeter (mm) of size frtion n w i is the weight of eh size frtion of ggregtes of totl smple. Wter infiltrtion Wter infiltrtion rtes were mesure using Cornell Sprinkle Infiltrometer (Cornell University, Ith, New York) (Ogen et l. 1997) lte July in 2011 for eh tretment plot. This system onsiste of portle rinfll simultor ple on single 24.1 m inner imeter ring inserte 7 m into the soil in etween rows. The ring ws equippe with n overflow tue to etermine the time to runoff n runoff rte. Rinfll simultor intensity rte of 0.45 m min 1 ws use. Every three minutes, runoff ws mesure until stey wter infiltrtion ourre. Wter infiltrtion rte (I r ) (m min 1 ) ws lulte y using the following eqution: [4] where r is rinfll intensity (m min 1 ), n r ot is the surfe runoff rte (m min 1 ). In ition, to ount for three-imensionl flow in the ottom of the ring, Reynols n Elrik (1990) evelope moel to estimte Fiel-Sturte Infiltrility (using single ring rin simultors), whih tkes into ount soil type n ring insertion epth effets on I r. They etermine empiril orretion ftors for ifferent soil texture n insertion epths to just fiel

27 15 mesurements of infiltrtion rtes. In this stuy, rings were inserte to soil epth of 15 m in silty ly lom soils. Therefore, onversion ftor of 0.80 ws use to tke into ount of horizontl flow t the ottom of the ring. The Horton s infiltrtion moel (Horton, 1940) ws use to esrie the exponentil ey of infiltrtion rte uring simulte 30 minute rinfll event: [5] were I r is in m min -1, F o is the initil infiltrtion rte m min -1, F is the finl infiltrtion pity (m min -1 ), is Horton s onstnt whih ws estimte for eh tretment plot, n t the elpse time (min). Sttistil nlyses Dt ws nlyze using the MIXED proeure of SAS (SAS Institute, 2002). Type of tillge ws onsiere s the min plot, resiue removl s the split-plot, n N fertiliztion s split- split-plot y yer n soil epth. Men seprtion ws etermine using the PDIFF proeure n signifine ws elre t evlute t p 0.10, unless otherwise stte. Aitionlly, orreltions were one using PROC CORR proeure in SAS. Results n Disussion Mngement effets on orn grin yiel The effets of resiue removl on orn grin yiel vrie y yer, site, tillge, n N fertiliztion rte (Fig. 2.3 n 2.4). Differenes in grin yiels ross yers n sites n e lrgely expline y previous verge yer yiels, ir temperture n rinfll t ollete in nery sites from 2000 through 2011 (unpulishe reserh of long-term tillge stuies, Al- Kisi, ). In 2009, grin yiels were lose to their verge mximum potentil for the AC n ASW sites t 12.7 n 15.5 Mg h -1, respetively. In 2010, grin yiels were lower ompre to 2009, ue to n unusully wet June n July, whih resulte in n itionl 100

28 16 mm umulte rinfll, 51% greter tht of the verge rinfll for this perio. In 2011 t the Ames site, grin yiels were reue ue to lk of rinfll in generl, espeilly in the month of July where these sites reeive 25 mm less umulte rin fll thn the previous verge uring this perio, n no rinfll just prior to the ritil grin filling stge. There ws signifint resiue removl effet on orn grin yiels for the AC site (Fig. 2.3), n the ASW site (Fig. 2.4). In the AC site, grin yiels were signifintly lower with 0% resiue removl ompre to 50 n 100% resiue removl tretments on verge y 8% greter ross ll yers. Similrly in the ASW site, grin yiels were signifintly lower with 0% resiue removl ompre to 50 n 100% resiue removl tretments y 10% on verge in 2009 n In 2011, there ws signifint tillge y resiue removl y N fertiliztion rte effet on grin yiels. Grin yiels were not signifintly ifferent ross tillge n resiue removl rtes with 280 kg N h -1 rte tretments. Uner N fertiliztion rtes of 170 kg N h -1, CT tretments on verge ws 7.33 Mg h -1 ross ll resiue removl tretments, n i not signifintly iffer from NT tretments with 50 n 100% resiue removl rtes. However, tretments with no resiue removl uner NT n 170 kg N h -1 fetliztion rtes were 16% lower thn CT tretments with no resiue removl n N fertiliztion of 170 kg N h -1. Lower yiels were oserve in NT tretments ompre to CT, on verge y 17% in the AC site ross ll yers. In the ASW site, NT tretments lso h signifintly lower yiels ompre to CT in 2009 n 2011on verge y 7%. However, in 2010, there ws signifint tillge y N fertiliztion rte intertion effet on yiels. Tretments tht reeive 280 kg N h -1, i not oserve ny signifint ifferenes in yiels etween NT n CT. Uner 170 kg N h -1 fertiliztion rte, CT tretments verge 9.57 Mg h -1 yiels, 4% greter tht of NT tretments.

29 17 In tretments in whih N fertilizer ws not pplie, verge yiels were 3.41 Mg h -1 uner CT tretments, 24% greter tht of NT. Stuies hve shown tht in soils similr to those in this stuy whih re high in ly ontent in the Corn Belt, exessive rop resiue left on the soil surfe suh s in NT, n potentilly slow own soil wrming in the spring n reue plnt emergene, N minerliztion, n rop growth resulting in lower rop yiels (Wolfe n Ekert, 1999; Al-Kisi n Kww- Mensh, 2007). From t ollete in Fig. 3.1 to 3.5, resiue removl effets on spring soil temperture n wter ontent y tillge n yer in the AC n ASW sites re shown in Figures 2.5 n 2.6. In the ASW site, soil tempertures strting in erly My until lte June when the orn nopy ompletely overe the soil surfe, were on verge o C ooler in NT tretments with 0% resiue removl thn NT tretments with 50 n 100% resiue removl (Fig. 2.6). Soil tempertures i not signifintly vry ross resiue removl rtes uner CT tretments, n were lso not signifintly ifferent when ompring CT with NT tretments with 50 n 100% resiue removl. Inresing N fertiliztion rtes from 170 to 280 kg N h -1 resulte in no signifint ifferenes in grin yiels ross resiue removl rtes n tillge systems in the ASW site in 2010 n These results re in greement with other stuies tht hve shown the NT systems require greter N fertiliztion input ue to low N minerliztion in oler, wetter soils uring the spring ompre to CT systems (Ksper et l., 1987; Vetsh n Rnll, 2000). Similr soil temperture results ourre in the AC site in 2009 n 2010, lthough, when soil onitions were rier suh s in 2011 (Fig. 2.5). Soil tempertures were signifintly wrmer uner NT tretments with 50 n 100% resiue removl ompre to CT tretments, ut not signifintly ifferent when ompring to 0% resiue removl tretments (Fig. 2.5). Inresing N fertiliztion rtes from 170 to 280 kg N h -1 i not offset yiel

30 18 reutions when onverting CT to NT systems in the AC site s it ws oserve in the ASW site. Uner NT mngement systems where rop resiue is left on the soil surfe, soil wter ontent is generlly greter thn CT systems throughout the growing seson. In the sene of growing plnts, the exess soil wter retes potentil prolems suh s poor germintion onitions in the spring, whih n reue rop yiel. This ws the se in the poorly-rine soils in the AC site, n to lesser extent in the well-rine soils in the ASW site in 2009 n The removl of rop resiue in these soils uner NT n e enefiil in terms of rop yiels for the first three yers of resiue removl in this stuy. Mngement effets on soil orgni ron n totl nitrogen fter three yers of resiue removl The effets of resiue removl on SOC ontent vrie y site, soil epth, tillge, n N fertiliztion rte (Tle 2.1 to 2.10). In the AC site, ifferenes mong mngement prties were only signifint in the top 15 m soil epth (Tle 2.1). At this soil epth, sine onverting from CT to NT, SOC ontent in NT tretments were on verge 27.9 Mg h -1, 11% greter ompre to CT tretments. Looking t the 0 to 60 m soil profile, SOC ontent in NT tretments were on verge Mg h -1, 9% greter thn CT tretments. Soil orgni ron sequestrtion rtes se on seline vlues prior to estlishment of tretments, i result in ifferenes mong mngement prties in the top 15 (Tle 2.1) n 0 to 60 m soil profile (Tle 2.5). For the 0 to 60 m soil profile, SOC sequestrtion rtes were greter with 0% resiue removl tretments ross tillge systems t 2.65 Mg C h -1 yr -1, ompre to 50 n 100% resiue removl tretments, whih ws on verge Mg C h -1 yr -1. Type of tillge lso h signifint effet of SOC sequestrtion rtes. On verge, for the 0 to 60 m soil profile epth, SOC sequestrtion rtes were 2.05 n 0.46 Mg C h -1 yr -1, uner NT n CT systems, respetively. Aitionlly, the highest SOC sequestrtion rtes when verge ross tillge n

31 19 resiue removl rtes ourre uner 280 kg N h -1 fertiliztion rtes t 1.89 Mg C h -1 yr -1, n erese with lower N fertiliztion rtes. However, there were no signifint ifferenes in TN ontent or sequestrtion rtes ross mngement prties t ny soil profile epth. In the ASW site, there were no signifint ifferenes in SOC ontent in the top 15 m soil epth mong mngement prties whih ws on verge ross ll tretments 19.9 Mg h -1 (Tle 2.6). In the 15 to 30 m soil profile epth, there ws signifint tillge n resiue removl effet on SOC ontent (Tle 2.7). The gretest SOC ontent ourre uner tretments with 0% resiue removl t Mg h -1, 7% greter thn 50 n 100% resiue removl tretments. Aitionlly, SOC ontent in CT tretments were on verge Mg h -1, 12% greter thn of NT tretments t the 15 to 30 m soil profile epth. At soil epths of 30 to 60 m, CT tretments ontinue to hve greter SOC ontent ompre to NT tretments on verge y 27% (Tle 2.8 n 2.9). Consequently, umultive SOC ontent t the 0 to 60 m soil profile uner CT tretments on verge, were signifintly greter t Mg h -1 ompre to NT tretments t Mg h -1 (Tle 2.10). However, SOC sequestrtion rtes for this site were in generl negtive regrless of tillge n resiue removl n N fertiliztion rtes t the soil profile of 0 to 60 m (Tle 2.10). SOC ontent losses were signifintly lower uner CT tretments t Mg C h -1 yr -1, ompre to NT tretments t Mg C h -1 yr -1. Inreses in SOC ontent were only oserve in the 15 to 30 m soil profile epth uner CT n 0% resiue removl tretments (Tle 2.7). There were no signifint ifferenes in TN ontent ross mngement prties t ny soil profile epth t the ASW site. However, TN sequestrtions rtes were signifintly greter uner CT tretments thn in NT t ll soil epth profiles (Tle 2.6 to 2.9). For the 0 to 60 m soil profile, TN sequestrtion rtes uner CT

32 20 tretments were on verge 0.08 Mg N h -1 yr -1 while NT tretments were signifintly lower t Mg N h -1 yr -1. In oth sites in generl, uner soil mngement systems in Iow with CT n 170 kg N h -1 fertiliztion rte n no resiue removl, SOC ontent remine reltively onstnt fter three yers. In the poorly-rine soils t the AC site, onverting from CT system to NT, ie in offsetting potentil SOC losses from resiue removl t the top 15 soil profile epth, n when summing SOC ontent t ll epths from 0 to 60 m. Inresing N fertiliztion rtes from 170 to 280 kg N h -1, lso ie in offsetting potentil SOC losses from resiue removl t the top 15 soil profile epth, n when summing SOC ontent t ll epths from 0 to 60 m. This ws expete ue to the strtifition of orgni C in the soil profile n ereses in soil orgni mtter minerliztion in wet n ol soil onitions, even when 50 n 100% of the resiue ws remove (Al-Kisi n Yin, 2005). However, in the well-rine soils suh s in the ASW site, ereses in SOC ontent were oserve t soil epths elow 15 m when onverting into NT systems. This oul e ttriute to reue potentil C inputs from ove- n elowgroun iomss (Tle 4.2), n lk of rop resiue inorportion into the soil in NT systems when ompring to CT (Strik et l., 1991). Resiue removl of 50% or greter resulte in negtive SOC sequestrtion rtes regrless of tillge or N fertiliztion rte, lthough these hnges in SOC ontent were not lrge enough to signifintly iffer from the seline vlues fter three yers for the ASW site. These results show the importne of smpling t soil epths to t lest elow the plow zone from previous n urrent mngement systems n in ontrsting soil types n limtes to e le to etermine sustinle mount of rop resiue removl in soils s impte y tillge systems n N fertiliztion rte on SOC sequestrtion (Do, 1998; Doln et l, 2006; Blno-Cnqui n Ll, 2007).

33 21 Due to the smll grul hnges in SOC ontent, eteting short term hnges re very iffiult in lrge prt ue to the high kgroun C levels n nturl vriility of soils. Miroil iomss ron (MBC), the living frtion of orgni mtter, hs een suggeste s sensitive mesure for hnges in orgni mtter sttus (Sprling, 1992). In oth sites in this stuy, there ws signifint tillge y resiue removl intertion effet on MBC (Fig. 2.7). In the AC site, the gretest MBC onentrtions ourre in NT tretments on verge of 570 μg C g -1 soil, n i not signifintly vry y resiue removl rte. Uner CT tretments, the gretest MBC onentrtions were 565 μg C g -1 soil with 0% resiue removl, n erese with resiue removl rte. In the ASW site, greter MBC onentrtions of 8% were oserve uner NT (509 μg C g -1 soil) tretments thn CT tretments (468 μg C g -1 soil). Signifint ereses in MBC onentrtions ue to resiue removl were only etete with the 100% removl rte n uner CT tretments. Mngement effets on selete soil physil properties fter three yers of resiue removl Bulk ensity (ρ ) vlues vrie y site n soil epth n were signifintly ffete y tillge, resiue removl, n N fertiliztion rtes (Tles 2.1 to 2.10). In the AC site, there ws signifint tillge y resiue removl y N fertiliztion rte effet on ρ for the top 15 m soil epth (Tle 2.1). In generl, the lowest ρ vlues ourre in 0% resiue removl tretments, n tretments in whih 280 kg N h -1 rte ws pplie. The highest ρ vlues ourre in tretments whih were uner NT n h 50 or 100% resiue removl. In the ASW site, there ws signifint tillge y resiue removl rte effet on ρ for the top 15 m soil epth (Tle 2.6). In generl, verge ρ with 0% resiue removl tretments ws 1.13 Mg m -3 ; 9% lower when ompre to NT tretments with 50 n 100% resiue removl, n CT tretments with

34 22 100% resiue removl. There were no signifint ifferenes mong mngement prties on ρ elow the 15 m soil epth. Soil penetrtion resistne (SPR) ws mesure s n initor for hnges in soil omption from ifferent resiue removl mngement prties (Fig. 2.8 n 2.9). The SPR mesurements were juste (A-SPR) to ommon vlue of soil grvimetri wter ontent of 0.27g g -1, to reue onfouning effets of soil grvimetri wter ontent t time of mesurements (Fig. 2.8 n 2.9). In the AC site, resiue removl of 50 n 100% resulte on verge A-SPR of 1.84 MP in the top 2.5 m soil epth, 13% greter thn when no resiue ws remove (Fig. 2.6). In the ASW site, A-SPR ws gretest with 100% resiue removl t 1.53 MP, n erese s resiue removl rte erese in the top 2.5 m soil epth (Fig. 2.9). These trens ontinue own to soil epths of 27.5 m in the AC site, n 17.5 m in the ASW site. Aitionlly in oth sites, NT tretments typilly h greter A-SPR when ompre to CT tretments in the top 2.5 m soil surfe. The exeption eing when SPR vlues were juste for soil grvimetri wter ontent in the AC site, NT tretments i not signifintly iffer from CT tretments (Fig. 2.8). In the ASW site, A-SPR in CT tretments ws signifintly greter thn NT tretments t soil epths etween 12.5 n 17.5 m, oiniing with the epth of hisel plow tillge (Fig. 2.9). This sme tren ws lso oserve in the AC site, lthough ifferenes etween tillge systems were not signifintly ifferent. Inreses in soil omption ue to resiue removl in this stuy n e ttriute to two ftors: (i) inrese fiel trffi when rop resiue is rke into rows, n then the olletion n trnsporttion wy from fiel, n (ii) reution of orgni mtter over perio of time whih stuies hve shown positive reltionship with stility of soil struture n opposite reltionship with ρ (Sone, 1990). Most stuies hve shown rpi inreses in soil omption

35 23 ue to resiue removl within yer, ue to fiel trffi n exessive rying in soils ue to leving soil surfe re (Quirog et l., 1999; Blno-Cnqui et l., 2006). After three yers of resiue removl in these sites; onverting urrent CT systems to NT to improve the stility of soil struture (Piere et l., 1994), or iniretly y root iomss y inresing N fertiliztion rte from 170 to 280 kg N h -1 (Rsool et l., 2008), i not signifintly reue the soil ompting effets (i.e. ρ n A-SPR) when 50% or greter of the resiue ws remove. Ajuste-SPR vlues in the AC site were signifintly orrelte with SOC ontent n MBC in the top 15 m soil epth (Tle 2.11). However, there were no signifint orreltions etween ρ n selete soil hemil n physil properties. In the ASW site, A-SPR n ρ were signifintly orrelte with SOC ontent, MBC, n MWD in the top 15 m soil epth (Tle 2.12). The stility of soil struture ws evlute y mesuring wter-stle ggregte (WSA) istriution, whih vrie y site n ws signifintly ffete y ifferent tillge, resiue removl, n N fertiliztion rte mngement prties (Fig n 2.11). The men weight imeter (MWD) ws lulte ross the seven ggregte size frtions, so tht with single vlue, omprisons n e me ross mngement prties (Fig n 2.13).In generl, the AC site h MWD of 1.31 mm, signifintly greter thn the ASW site whih on verge ws 1.22 mm. In the AC site, there ws signifint tillge y resiue removl intertion effet, s well s n N fertiliztion effet (Fig. 2.12). The gretest MWD vlues ourre with NT tretments with 0% resiue removl t 1.58 mm. The next highest MWD vlues were uner CT tretments with 50 n 100% resiue removl whih verge 1.25 mm. While the lowest MWD vlues ourre uner NT tretments with 50% resiue removl, n 100% resiue uner CT n NT tretments on verge t 1.04 mm. Aitionlly, tretments whih i not reeive ny N, h signifintly lower MWD vlue on verge of 20% ompre to when 170 n 280 kg N