Dryland cropping systems influence the microbial biomass and enzyme activities in a semiarid sandy soil

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1 University of Nersk - Lincoln DigitlCommons@University of Nersk - Lincoln Pulictions from USD-RS / UNL Fculty U.S. Deprtment of griculture: griculturl Reserch Service, Lincoln, Nersk 11 Drylnd cropping systems influence the microil iomss nd enzyme ctivities in semirid sndy soil Veronic cost-mrtinez USD-RS, veronic.cost-mrtinez@rs.usd.gov Roert Lscno USD-RS Frncisco Clderón USD-RS Jill D. ooker USD-RS Ted M. Zoeck USD-RS, ted.zoeck@rs.usd.gov See next pge for dditionl uthors Follow this nd dditionl works t: cost-mrtinez, Veronic; Lscno, Roert; Clderón, Frncisco; ooker, Jill D.; Zoeck, Ted M.; nd Upchurch, Dn R., "Drylnd cropping systems influence the microil iomss nd enzyme ctivities in semirid sndy soil" (11). Pulictions from USD-RS / UNL Fculty.. This rticle is rought to you for free nd open ccess y the U.S. Deprtment of griculture: griculturl Reserch Service, Lincoln, Nersk t DigitlCommons@University of Nersk - Lincoln. It hs een ccepted for inclusion in Pulictions from USD-RS / UNL Fculty y n uthorized dministrtor of DigitlCommons@University of Nersk - Lincoln.

2 uthors Veronic cost-mrtinez, Roert Lscno, Frncisco Clderón, Jill D. ooker, Ted M. Zoeck, nd Dn R. Upchurch This rticle is ville t DigitlCommons@University of Nersk - Lincoln:

3 iol Fertil Soils (11) 7:55 7 DOI 1.17/s ORIGINL PPER Drylnd cropping systems influence the microil iomss nd enzyme ctivities in semirid sndy soil Veronic cost-mrtínez & Roert Lscno & Frncisco Clderón & Jill D. ooker & Ted M. Zoeck & Dn R. Upchurch Received: 1 Mrch 1 /Revised: 11 Ferury 11 /ccepted: 19 Ferury 11 /Pulished online: 3 My 11 # Springer-Verlg (outside the US) 11 USD disclimer Trde nmes nd compny nmes re included for the enefit of the reder nd do not infer ny endorsement or preferentil tretment of the product y USD-RS. USD is n equl opportunity provider nd employer. V. cost-mrtínez (*) : R. Lscno : J. D. ooker : T. M. Zoeck Cropping Systems Reserch Lortory, Wind Erosion nd Wter Conservtion Unit, USD-RS, 31 th St., Luock, TX 7915, US e-mil: veronic.cost-mrtinez@rs.usd.gov F. Clderón Centrl Gret Plins Resources Mngement Reserch, USD-RS, 335 County Rod GG, kron, CO 7, US D. R. Upchurch Southern Plins re, USD-RS, 11 Hollemn Drive Est, College Sttion, TX , US strct Indictors of soil qulity, such s microil iomss C nd N (MC, MN) nd enzyme ctivities (Es), involved in C, P, N, nd S cycling, s ffected y drylnd cropping systems under conventionl (ct) nd no tillge (nt) prctices were evluted for 5 yers. The soil is sndy lom with n verge of 1.% cly, 7.% snd, nd.5 g kg 1 OM t 1 cm. The crops evluted were rottions of grin sorghum (Sorghum icolor L.) or forge sorghum (lso clled hygrzer), cotton (Gossypium hirsutum), nd winter rye (Secle cerele): grin sorghum cotton ( Ct), cotton winter rye sorghum (Ct Rye ), nd forge sorghum winter rye ( Rye). The tillge tretments did not ffect soil M nd Es of C cycling (i.e., β-glucosidse, β-glucosminidse, α- glctosidse), P cycling (lkline phosphtse, phosphodiesterse), nd S cycling (rylsulftse) except for seprtion due to tillge for Rye nd Ct Rye oserved in PC plots when ll Es were evluted together. fter 3 yers, rottions with winter cover crop history (Ct Rye nd Rye) enhnced soil MN (up to 3%) nd Es (1-37%) compred to Ct. fter 5 yers, Ct nd Ct Rye showed similr soil MC, MN, Es, totl cron (TC), nd orgnic cron (OC). comprison of Ct plots with nery continuous cotton (Ct Ct) reserch plots in the sme soil reveled tht it took 5 yers to detect higher TC (%), MC (3%), nd Es (3 3%, depending on the enzyme) under Ct. The significnt improvements in M nd Es found, s ffected y drylnd cropping systems with history of winter cover crops nd/or higher iomss return crops thn cotton, cn represent chnges in soil OM, nutrient cycling, nd C sequestrtion for sndy soils in the semirid Texs High Plins region. It is significnt tht these soil chnges occurred despite summer crop filure (3 nd ) nd lck of winter cover crops () due to lck of precipittion in certin yers. Keywords GRCEnet. Oglll quifer. FME nlysis. Microil iomss. Drylnd. Cotton. Cropping systems Introduction Drylnd cropping systems depend on wter from precipittion, which is significnt limiting fctor for production in semirid regions including the Texs High Plins (THP), which receives out 7 mm of nnul precipittion (Lscno ). Most soils in THP re sndy nd hve een under cotton-sed cropping systems since the 19s, contriuting to low orgnic mtter (OM), <1%, due to the low iomss return with intensive tillge nd

4 5 iol Fertil Soils (11) 7:55 7 winter fllow prctices (cost-mrtínez et l. ; llen et l. 5, ). Sustinle griculturl production systems in the semirid THP require drylnd cropping systems tht led to improvements in soil qulity nd functioning y incresing iomss return with minimum tillge prctices nd crop rottions with sorghum, which is drought-tolernt crop. Increses in oth OM qulity nd quntity cn hve eneficil effects on soil qulity ecuse OM is relted to ggregtion, soil structure, nd wter infiltrtion nd vilility for crop production (Dorn nd Prkin 199; Frnzlueers ). Chnges in soil OM tke too long to e detected; however, soil microil communities nd ctivities cn provide erlier trends of chnges in soil OM s ffected y cropping systems. Microil communities ply role in the decomposition of orgnic mterils nd plnt residues incorported into the soil, leding to energy flow, nutrient cycling, nd OM uild-up or soil C sequestrtion (Lynch nd rgg 195; Kndeler et l. 199). Microil iomss C (MC) nd N (MN) comprise 1% to 3% of totl soil C nd up to 5% of totl N in soils, respectively, ut MC nd MN re the most ctive frctions of the totl soil OM (Smith nd Pul 199; Frnzlueers et l. 199). Previous studies showed tht microil communities recycle nd trnsform nutrients in soil through enzyme-medited rections (Kndeler et l. 199), which cn e determined y simple, sensitive, nd reltively rpid protocols compred to other iochemicl nlyses (Ndiye et l. ; Nnnipieri et l. ). Cron-cycling enzyme ctivities (Es) such s those of β- glucosidse, α-glctosidse, nd β-glucosminidse distinguished cropping system-induced differences in residues degrdtion nd nutrient incorportion in soil ecuse these enzymes prticipte in the degrdtion of plnt components such s celloiose, meloiose, nd chitin (cost-mrtínez et l. 7; Sotomyor-Rmírez et l. 9). lso, β- glucosminidse ctivity is involved in N-cycling s it is involved in chitin degrdtion (Prhm nd Deng ) nd hs een correlted to N minerliztion in soils (Tti et l. 1). fter N, P is the second most limiting soil nutrient for cotton (Gossypium hirsutum L.) production in the Southern High Plins (ronson et l. 1). Therefore, n evlution of soil phosphtses, involved in the minerliztion nd trnsformtion of P in soil, my provide informtion for one to evlute cotton productivity. Similrly, n evlution of rylsulftse ctivity cn provide informtion on the minerliztion nd trnsformtion of S compounds in soil, which is essentil for plnt nutrition. Studies in other regions indicte tht cropping systems with diversified crops under conservtion tillge cn enhnce soil microil iomss nd ctivity y incresing the residue input into the soil nd reducing soil disturnce nd erosion (Dorn nd Prkin 199; Moore et l. ; Frnzlueers ). Furthermore, the type nd quntity of plnt residues tht the cropping systems provide long with tillge prctices will influence the soil properties differently (Lieig et l. ). n dditionl fctor tht ffects soil properties is the length of estlishment, i.e., period of the cropping system (cost- Mrtínez et l. 7, ). Previous studies in semirid regions hve emphsized the chllenge of enhncing soil microil communities in drylnd cropping systems with low levels of iomss production due to low rin nd extreme mient tempertures (Ryn 1999; Lieig et l. ). Currently, there is little informtion on sensitive soil qulity prmeters, i.e., MC, MN, Es, s ffected y the cropping systems under drylnd conditions in sndy soils, where climtic vritions cuse differences in iomss production or crop filure nd thus disrupt cropping sequence. Therefore, our first ojective ws to mesure crop iomss production over the first 5-yer period under drylnd reserch plots in semirid climte with different tillge prctices nd crop rottions of winter rye (Secle cerele), forge or grin sorghum (Sorghum icolor), nd cotton. The resulting cropping systems included grin sorghum cotton ( Ct), cotton winter rye grin sorghum (Ct Rye ), nd forge sorghum winter rye ( Rye), mnged under no tillge (nt) nd conventionl tillge (ct) prctices. Our second ojective ws to evlute how the different drylnd cropping systems ( Ct, Ct Rye, nd Rye) nd tillge prctices, nt nd ct, would modify the soil microil iomss (MC nd MN) nd severl enzyme ctivities of C, N, P, nd S cycling. lso, M nd Es under Ct were compred to the common cropping system in this region, i.e., cotton monoculture (Ct Ct) under ct. Our third ojective ws to explore the correltions mong soil properties nd to determine if chnges in soil M nd/or Es in our lst smpling (representing yer 5) would predict the cotton lint yields for the following yer (representing yer ), when ll the cropping systems were plnted with cotton. Mterils nd methods Cropping systems nd tillge tretments This drylnd reserch study ws estlished t the USD- RS frm ner New Del, TX, US (33 N, 11 9 W nd verge elevtion of 9 m ove se level). Prior to this study, the lnd ( h) ws fllow during fll of 1, cotton ws plnted in summer, nd rye ws grown from Decemer to pril 3. The soil is clssified s Olton sndy lom (fine, mixed, superctive, thermic ridic Pleustolls) with n verge of 1.% cly, 7.% snd,

5 iol Fertil Soils (11) 7: nd.5 g kg 1 OM. In summer 3, the field ws divided into three replictes of split-plot design, with cropping systems s the min tretment nd tillge s suplots (ech plot ws 1 m in length). description of the cropping systems nd tillge suplots follows. Three cropping systems in order of incresing cropping intensity (CI) re descried s follows: 1. Ct Rottion of cotton nd sorghum without winter cover crop. This rottion represents out 5% of CI ecuse of the fllow periods without winter cover crop.. Ct Rye Rottion of cotton nd sorghum every summer with winter cover crop (rye). This rottion represents out 1% of CI ecuse of using summer nd winter crop during the yer (when possile). 3. Rye High iomss cropping system with high residue crops during summer nd winter, representing out 1% of CI. This system did not include cotton crop s it hs een previously reported tht cotton produces less residue per hectre thn the other mjor crops (Unger nd Prker 197; Ll ), nd thus our ojective ws to investigte the mximum impct chievle on the soil properties. The two tillge tretments re descried s follows: 1. No tillge The summer ove-ground crop residues were left undistured on the soil surfce. Forge sorghum (hygrzer) nd grin sorghum were lid down y grin drill nd left on the surfce, wheres cotton stlks remined stnding.. Conventionl tillge Summer crops were shredded nd incorported while mixing the soil up to 15 cm fter hrvest every fll. For tretments with winter cover crop, plots were listed to crete eds, 1 m prt, nd rye ws plnted every fll t kg h 1 on respective tretments. eds were prepred (ed prep) gin efore plnting (sme dy) every My for rottions under this tillge tretment. The cropping systems nd tillge prctices mentioned erlier were replicted three times using rndomized lock design. s seline, we used the common cropping system in the THP, i.e., tilled cotton monoculture (Ct Ct) from nery reserch plots on the sme soil. Generl crop mngement Crops were generlly plnted in My. The forge sorghum (hygrzer) vriety Pcesetter 1 ws plnted t rte of 1. kg h 1 with drill t.-m spcing. Cotton, vriety Pymster 3-rr, ws plnted t rte of 9 11 kg h 1 nd grin sorghum, vriety K35-Y5, ws plnted t rte of 3 kg h 1, oth on 1-m row spcing. Pesticides nd fertilizer were pplied fter rinfll events, which is typicl mngement prctice for drylnd crops in the THP. For weed control, Mrksmn (Dicm nd trzine) hericide ws spryed on forge nd grin sorghum in July (.3 L h 1 ), nd Round-up (Glyphoste) hericide ws spryed on cotton (.3 L h 1 ). Cotton ws generlly chemiclly terminted nd defolited round mid-octoer using 1.17 L Cyclone (Prqut dichloride) h 1. When rin ws sufficient, the winter cover crop (rye) ws plnted in Decemer nd terminted during pril of the next yer using the hericide Round-up (Glyphoste) t.3 L h 1 in Ct Rye nd Rye rottions. Climte dt nd crop mesurements Climte dt (precipittion nd ir tempertures) were otined from the wether sttion locted ner these reserch plots. Crop iomss (cotton nd forge nd grin sorghum) ws determined three times during the yer sed primrily on the growth stges of cotton since this crop hs more definitive growth stges thn forge or grin sorghum: first squre in mid-june, first loom the first week of July (when t lest 5% of the plnts hve flowers), nd pek loom in ugust. The results from ugust smplings will e reported in this pper. The crop iomss smples were rndomly tken from 1-m re from the three field replictes of tretment plot t three loctions (north, center, nd south prt) in ech plot (n=9). iomss smples were tken from the winter cover crop following the sme protocol of the summer crops. Soil smpling nd mesurements Soil smples t 1 cm in depth were collected using hnd uger. For ech plot, composite smples were tken from the south nd north end of the field, for totl of six smples per cropping system nd tillge tretment comintion (two soil smples per plot three field replictes). The smples were tken in Novemer 3, 5, nd 7, representing the strt nd 3 nd 5 yers of the study, respectively. dditionlly, soil smples were tken in July 1 Mention of this or other proprietry products is for the convenience of the reders only nd does not constitute endorsement or preferentil tretment of these products y USD-RS.

6 5 iol Fertil Soils (11) 7: nd these were used to evlute the chnges in M nd Es during nd fter the 5 growing seson. Soil smples, used for seline, were tken from Ct Ct under ct from nery field (n=3). For soil M nlyses, the soil smples were sieved (<5 mm) nd stored t C until nlyses were performed within the next weeks. Soil grvimetric wter content ws determined fter drying the smples t 15 C for h. The MC nd MN contents were determined on fieldmoist soil (15 g oven-dry equivlent) smples y the chloroform fumigtion extrction method using.5 M K SO s n extrctnt (rookes et l. 195; Vnce et l. 197). riefly, orgnic C nd N extrcted from the fumigted ( h) nd non-fumigted (control) soil were quntified y CN nlyzer (Shimdzu Model TOC V/CPH -TN, Shimdzu Corp., Kyoto, Jpn). The MC nd MN, difference etween fumigted nd non-fumigted vlues, were clculted using kec fctor of.5 (Wu et l. 199) nd ken fctor of.5 (Jenkinson 19), respectively. The Es, β-glucosidse, α-glctosidse, β- glucosminidse, lkline phosphomonoesterse, phosphodiesterse, nd rylsulftse, were ssyed using 1 g of irdried soil with their pproprite sustrte nd incuted for 1 h (37 C) t their optiml ph s descried y Tti (199) nd Prhm nd Deng () for β-glucosminidse ctivity. The Es were ssyed in duplicte with one control, to which sustrte ws dded fter incution (product of ll rections is PN= P-nitrophenol). In ddition, soil C (orgnic nd totl) nd totl N, P, nd NO 3 N (ville N) were determined in ir-dried soil smples (Wrd Lortories, Nersk) y utomted dry comustion (LECO TruSpec CN), the Mehlich P-3 method (Mehlich 19), nd N KCl extrction method (Keeney nd Nelson 19), respectively. Soil ph ws mesured in the ir-dried soil (< 5 mm) using comintion glss electrode (soil/wter rtio, 1:.5). Sttisticl nlyses Most dt were nlyzed s split-plot rndomized lock design with the Proc Mixed Procedure with cropping systems ( Ct, Ct Rye, nd Rye) s the min tretment nd tillge (nt nd ct) s suplots y using SS softwre (v , Cry, NC, US). lthough there were no tillge tretment effects for ll the properties evluted in this study, r grphs were prepred with lest significnt differences (LSDs) for tilled nd no-tillge plots individully. lso, stndrd errors were clculted (SigmPlot, v. 11, Systt Softwre, Inc., Sn Jose, C, US) for ll r grphs s ll replictes for plnt (n=9) nd soil (n=) mesurements were included. Stndrd errors were lso clculted for the comprison of soil properties in Ct nd Ct Ct. Three-dimensionl (3D) plots were used to compre ll cropping systems nd tillge tretment comintions ccording to three relted E of C cycling (β-glucosidse, α-glctosidse, nd β-glucosminidse) or P nd S cycling (lkline phosphomonoesterse, phosphodiesterse, nd rylsulftse). contrst comprison ws performed (non-orthogonl) to investigte if there were significnt differences etween the E in soil under Ct compred to Ct Rye or Rye. In these 3D plots, results from Ct Ct under ct were included ut not tested in the contrst comprison s this site is outside of the field with the cropping systems nd tillge tretment comintions previously descried. Principl component nlysis (PC) ws conducted in the PCORD progrm (Version 5) to determine differences in the soil metolic functioning mong the systems using ll Es together (β-glucosidse, α-glctosidse, β-glucosminidse, lkline phosphtse, phosphodiesterse, nd rylsulftse). monotonic trnsformtion (squre root) of ll Es ws lso conducted to crete more normlly distriuted dt set nd to reduce the coefficient of vrition for individul Es. The squre root trnsformtion is similr in effect to the logrithmic trnsformtion ut less drstic nd is commonly used in ecologicl studies (McCune nd Mefford 1999). The PCs were performed using cross-product mtrix with vrince covrince centered nd clculting scores for Es y weighted verging. Results nd discussion Climte influence on crop estlishment, mngement, nd crop properties The totl mount nd distriution of precipittion etween 3 nd 7 vried from the nnul verge of 7 mm (Fig. 1). The minimum mount of rin ws mm in 3 nd the mximum ws 9 mm in, ech representing 1-yer record-low nd record-high rinfll for this region, respectively. Thus, 3 ws chllenging yer to egin this drylnd study s crops filed y the end of July due to insufficient rin. Nevertheless, this yer ws included in our mngement history nd is n Fig. 1 Profile dt from 3 to 7 of the loction of the study including ir temperture nd precipittion () nd crop iomss (). For ech figure in, the crop present during tht growing seson is shown in old, nd the rs with different letters within the sme tillge tretment represent significnt differences t P<.5. Ech figure in lso shows the cumultive het units (HU) for ech crop (reported s degree Celsius per dy), which re clculted s the verge dily temperture minus threshold temperture (cotton=15.5 C nd grin or forge sorghum=1 C) times the totl numer of dys in the growing seson (emergence until hrvest)

7 g iol Fertil Soils (11) 7: ) Tot Rin (mm) verge ir Temp (C) ) kg h ug 19, 3 HU Ct = 13 HU Srf =35,1951 HU Srg =53 No-tillge Conv. tillge -Rye ug 1, Ct-Rye- -Ct HU Ct = 157 HU Srf =31 HU Srg =39 c Climte dt Rinfll (mm) ir temperture ( o C) Plnt iomss kg h -1 kg h Rye ug 17, 5 -Rye ug 1, Ct-Rye- -Ct C Ct-Rye- -Ct c -Rye Ct-Rye- -Ct ug 1, 7 c C HU Ct = 19 HU Srf =15 HU Srg =15 HU Ct = 911 HU Srf =93 HU Srg =93 HU Ct = 3 HU Srf =199 HU Srg =199 Jn Fe Mr pr My Jun Jul ug Sep Oct Nov Dec -Rye Ct-Rye- -Ct

8 iol Fertil Soils (11) 7:55 7 exmple of crop filure, which cn e expected for drylnd cropping systems in semirid region (Tle 1). Plnt iomss for grin nd forge sorghum nd for cotton crops were <5, kg h 1 in ugust 3 while plnt iomss for ugust were, kg h 1 for cotton,, kg h 1 for grin sorghum, nd 17, kg h 1 for forge sorghum (Fig. 1). Further, given the low precipittion for 3, the winter cover crop (rye) ws not plnted in the Ct Rye nd Rye tretments until. However, winter cover crops were possile during due to the record-high precipittion. In 5, totl precipittion of 5 mm ws elow the long-term verge, ut dequte rin ws received from Jnury to Octoer, with low precipittion in pril nd Septemer (Fig. 1). Thus, plnt iomss in ugust 5 (nd ) ws etween nd times higher thn those in ugust 3 for ll crops, regrdless of the cropping system nd tillge prctice (Fig. 1). The 5 winter cover crop ws plnted in Mrch nd terminted in My nd thus provided soil surfce cover for few weeks only. In, totl precipittion ws 99 mm, similr to the mount oserved in 3 (Fig. 1). The winter rye crop hd to e plnted in Ferury of this yer. However, due to lck of wter, it did not emerge until Mrch nd ws then terminted on 1 My. s consequence, it hd low residue on the soil surfce for the Ct Rye nd Rye plots. ecuse of low rinfll, i.e., < mm, etween June nd ugust, the conditions were too dry to pply fertilizers nd to sustin the summer crop (Tle 1). In ugust, crop iomss ws similr to those for the sme month in 3 (Fig. 1). For this yer, cotton ws not hrvested ecuse the plnts were shorter thn verge nd cnnot e hrvested y cotton stripper. t the end of this yer, it ws not possile for the winter cover crop to e plnted due to extremely low rinfll. In the 7 growing seson, cotton production ws suject to lower ir tempertures nd higher precipittion t the eginning of summer; precipittion ws close to verge nd wrmer ir tempertures occurred in the erly fll. The 7 crop iomss ws up to five times higher (i.e., forge sorghum) thn in 3 nd due to the wet conditions Tle 1 Cropping systems mngement detils nd summry of crop yields nd cotton lint Cropping system mngement 3 3/ /5 5 5/ /7 7 7/ Summer Winter Summer Winter Summer Winter Summer Winter Summer Winter Summer Rye Rye Rye Rye Rye Rye Ct Emergence 1-Jun 15-Dec 1-My 15-Dec 1-Jun 15-Mr 9-Jun 13-Fe 3-My Too dry Hrvest -pr -pr 1-My 1-My Yield (nt) 1, 1,71 13, ,7 Yield (ct),1 1,5 13,3 7 39, 51 Ct Rye Ct Rye Rye Ct Rye Rye Ct Rye Ct Emergence -Jun 15-Dec 19-My 15-Dec 3-My 15-Mr 1-Jun 13-Fe 11-Jun Too dry Hrvest -Oct -pr 1-Nov -pr 1-Oct 1-My 1-Jn (7) 1-My -Oct Yield (nt) 91 1,1 3 Yield (ct) ,1 31 Ct Fllow Ct Fllow Fllow Ct Fllow Fllow Ct Emergence -Jun 17-My 1-Jun 9-Jun 3-My Hrvest Too dry 15-Oct -Nov 17-Nov 17-Oct Yield (nt) Yield (ct) 17 Ct Ct , 9 Fertilizer for ll kg h 1. kg N h 1 kg N h 1 kgh 1 kgh 1 ppliction dte 5-pr 1-My Yields (kg h 1 ) re reported s ugust iomss mesurements for grin nd forge sorghum, except for cotton, which re the lint Ct Ct continuous cotton, Ct grin sorghum cotton, Ct Rye cotton winter rye grin sorghum, Rye forge sorghum winter rye, nt no tillge, ct conventionl tillge

9 iol Fertil Soils (11) 7: during the first months of the yer (Fig. 1). However, they were 1.5 times lower thn in 5 ecuse precipittion ws too high nd mient tempertures were too cold during most of the summer. The winter cover crop ws not plnted in 7 due to insufficient precipittion during the winter. nnul vritions in iomss production during this 5-yer period provide evidence tht low rinfll will produce low iomss nd C inputs in drylnd cropping systems for this region; result tht hs een reported for nother semirid region (Lieig et l. ). In generl, the cotton iomss from the nery drylnd Ct Ct plots, seline, ws similr to the cotton iomss of ny rottion studied (Tle 1). Thus, cotton lint yields were not influenced y crop rottion or tillge history during the 5 yers of our study (3 7). However, cotton lint were higher under Rye compred to the other cropping systems in, when cotton ws grown in ll these drylnd cropping systems, nd there were no differences due to tillge prctices (Tle 1). In contrst, Feng et l. (3) reported % higher lint yield for no-till tretment compred to conventionl-till tretment fter yers for silt lom soil with continuous cotton. This result suggest tht increses in cotton lint yield due to cropping system nd tillge mngement re possile ut will require more thn 5 yers to detect the effects of crop rottions nd tillge prctices on cotton lint yield. Soil totl C, totl N, microil iomss C nd N Minimum tillge provides n extensive rooting system nd soil surfce protection with crop residues, which hs influenced increses in M for soils of higher OM thn the soil evluted here, nd these increses in M hve een ssocited with positive chnges in soil qulity nd C sequestrtion (Krlen et l. 1999; Moore et l. ; cost-mrtínez et l., 1; Sotomyor-Rmírez et l. 9). In this study, it ws not expected tht soil totl C (TC) nd totl N (TN) would e impcted y the tillge tretments fter 5 yers (Tle ), ut it ws surprising tht MC nd MN were not ffected y the tillge tretments s they represent the living nd iologiclly most ctive frction of SOM (Fig. ). It is possile tht chnges in M my tke longer for sndy soils in semirid climte with no tillge prctices under drylnd cropping systems. For exmple, Feng et l. (3) reported increses in SOC (13%), totl N (7%), nd MC (up to 1%) in the surfce lyer of silt lom under nt continuous cotton for yers when compred to ct. nother study provided evidence of higher cotton root iomss production nd C concentrtions under nt thn ct in surfce soils (Sinju et l. 5). More highly minerlized C nd N, up to 15 cm in depth under reduced tillge thn ct, demonstrted increses in nutrient cycling with chnged rhizosphere environment nd microil communities under minimum tillge (Wright et l. ). Cropping systems did not impct soil TC nd TN until yer 5whensoilunder Rye showed higher TC nd TN thn the other drylnd cropping systems (Tle ). However, rottions with winter cover ( Rye nd Ct Rye ) showed higher MC (up to 5%) nd MN (up to 3%) compred to rottion without winter cover crop ( Ct) fter only 3 yers s shown in Fig. (July 5) nd Fig. 3 Tle Selected soil properties under different the drylnd cropping systems evluted Cropping Orgnic C Totl C Totl N NO 3 N P Soil ph Soil moisture System No-till Till No-till Till No-till Till No-till Till No-till Till No-till Till No-till Till gkg 1 soil mg kg 1 soil % Nov. 3 ( eginning of the study) Rye n.d. n.d Ct Rye n.d. n.d Ct n.d. n.d Nov. 5 (yer 3 of the study) Rye n.d. n.d c Ct Rye n.d. n.d Ct n.d. n.d Nov. 7 (yer 5 of the study) Rye Ct Rye Ct Different letters indicte significnt differences mong cropping systems for ech yer from LSDs t P<.5 Ct Ct continuous cotton, Ct grin sorghum cotton, Ct Rye cotton winter rye grin sorghum, Rye forge sorghum winter rye, nt no tillge, ct conventionl tillge

10 iol Fertil Soils (11) 7: Nov 3 under drylnd conditions nd/or this soil type. Further, comprison of Ct plots with Ct Ct in nery plots showed tht soil M ws higher y 3% under Ct thn Ct Ct fter 5 yers of estlishment of the lterntive cropping system (Tle 3). These findings suggest tht soil microil iomss in cotton-sed cropping systems, without winter cover crops, my e more sensitive to environmentl disturnces common for semirid regions, such s periods of Microil iomss C (mg C kg -1 soil) July 5 Nov 5 Nov 7 C C Microil iomss N (mg N kg -1 soil) Nov 3 July 5 Nov 5 -Rye Ct-Rye- -Ct Fig. Soil MC s ffected y the cropping systems nd tillge tretments. Smples were tken from to 1 cm in Nov 3 (initition of the study), Nov nd July 5 (3 yers), nd Nov 7 (5 yers of the study). rs with different letters within the sme tillge tretment represent significnt differences t P<.5 (July nd Nov smplings), respectively. These findings demonstrte erly impcts, fter 3 yers, in microil iomss despite vritions in crop iomss produced every yer for this sndy soil. y the Nov 7 smpling, representing 5 yers of this study, MC nd MN were similr in soil under Ct Rye nd Ct. These results suggest tht cropping system without winter cover crop, e.g., Ct, would need longer time to rech soil M levels of rottion with winter cover crops such s Ct Rye Nov 7 -Rye Ct-Rye- -Ct Fig. 3 Soil MN s ffected y the cropping systems nd tillge tretments. Smples were tken from to 1 cm in Nov 3 (initition of the study), Nov nd July 5 (3 yers), nd Nov 7 (5 yers of the study). rs with different letters within the sme tillge tretment represent significnt differences t P<.5

11 iol Fertil Soils (11) 7: Tle 3 Comprison of selected soil properties in grin sorghum cotton nd continuous cotton oth under conventionl tillge prctices Soil property Smpling (Nov.) Ct Ct Ct Difference etween Ct compred to Ct Ct (%) Totl C (g kg 1 soil) 5. (.).75 (.1) _ 7.3 (.) 5.1 (.) 1 MC (mg kg 1 soil) 5 5. (3.5) 53.3 (.3) (1.9) 5. (.) 3 MN (mg kg 1 soil) 5. (.77).13 (.57) _ 7.7 (.).5 (.9) β-glucosidse ctivity (mg PN kg 1 soil h 1 ) (1.11) 1.7 (1.97) _ (.3) 55.5 (.5) 3 β-glucosminidse ctivity (mg PN kg 1 soil h 1 ) 5. (.).35 (.7) (.5) 7.39 (.5) 5 α-glctosidse ctivity (mg PN kg 1 soil h 1 ) (.1) 1.5 (.35) _ 7 1. (.) 3. (.1) 3 lkline phosphomonoesterse ctivity (mg PN kg 1 soil h 1 ) 5 5. (.3) 57.9 (.51) _ (.5) (.1) Phosphodiesterse ctivity (mg PN kg 1 soil h 1 ) 5 3. (.5).55 (1.13) _ (.9) 3.1 (.5) rylsulftse ctivity (mg PN kg 1 soil h 1 ) (.13).5 (.3) (.3).7 (.3) The Ct Ct (ct) is locted in nery reserch site, which hs shown generlly consistent vlues for these properties over yers. In Nov, MC (.3 mg N kg 1 soil) or MN (5.7 mg N kg 1 soil) nd the ctivities (mg PN kg 1 soil h 1 )ofβ-glucosminidse (3.3), β-glucosidse (3.97), α-glctosidse (1.1), lkline phosphomonoesterse (.3) phosphodiesterse (1.37), nd rylsulftse (1.1) were close to vlues reported here for Nov 5 nd 7. Vlues in prenthesis represent the stndrd error from the men for Ct (n=) nd Ct Ct (n=3) high mient tempertures nd low precipittion, interrupted y periods of sudden rin events nd wind-induced soil erosion during winter fllow periods (cost-mrtínez et l. 7). In fct, the environmentl conditions during this 5-yer study resulted in different crop iomss production ech yer, which could e responsile in prt for preventing the increse in soil microil iomss y the crop rottion history of cotton nd sorghum erlier (Smith nd Pul 199; Stromerger et l. 7). Our smpling times every Novemer, however, occurred t post-hrvest when wether nd soil conditions re most stle for comprisons of the soil microiologicl chrcteristics s recommended y Lieig et l. (). Enzyme ctivities Tillge tretments did not ffect the three relted Es of C cycling or the Es relted to P nd S cycling (lkline phosphomonoesterse nd phosphodiesterse nd rylsulftse) ccording to 3D plots (Fig. ). The lck of significnt tillge effects on the soil M nd Es fter 5 yers is surprising result s other studies hve reported shifts in microil communities due to tillge (Wortmnn et l. ). For exmple, higher fungl popultions (i.e., phospholipid ftty cids indictors) under no-till soils compred to tilled counterprts cn led to increses in Es (Roldn et l. 5; Kennedy nd Schillinger ). Our results my e ttriuted to the high nnul vriility of plnt iomss production during the study with yers of very low residue ccumultion in the soil surfce under the no-till tretment plots, which my hve not exceeded the tilled plots. Cropping systems with winter cover crops ( Rye nd Ct Rye ) showed cler seprtion from those without winter cover crops history ( Ct nd Ct Ct) in 3D plots for smples tken fter 3 yers (July nd Nov 5) due to higher Es of C cycling (Fig., ) or P nd S cycling (Fig. d, e). significnt seprtion mong cropping systems ws detected, ut there were no significnt differences in soil Es under Ct Rye vs. Rye or Ct vs. Ct Ct. The erly trends from this study in sndy soil t the THP gree with studies reporting tht M nd rylsulftse nd β-glucosidse ctivities were sensitive to lterntive mngement prctices, including winter cover crop fter only 1 yers t 7.5 cm (Ndiye et l. ; Schutter et l. 1). The use of rye winter cover crop must hve incorported higher iomss in soil nd/or the dditionl rhizosphere effect must hve incresed microil iomss nd the production of enzymes during winter when compred to cropping systems without winter cover crops ( Ct nd Ct Ct). The yield produced nd/or the soil surfce coverge y rye during winters ws not significnt

12 iol Fertil Soils (11) 7:55 7 β-glucosminidse ctivity ) July 5 Nov 5 5 ) c) Ct-Rye- (nt) 1 α-glctosidse ctivity -Rye (ct) Ct-Rye- (ct) -Ct (nt) -Rye (nt) Ct-Ct (ct) Ct (ct) 1 1 α-glctosidse ctivity Ct-Rye- (nt) -Rye (ct) -Rye (nt) -Ct (nt) Ct-Ct (ct) Ct-Rye- (ct) Ct (ct) 1 1 α-glctosidse ctivity -Rye (nt) -Rye (ct) Ct-Rye- (nt) -Ct (ct) Ct-Ct (ct) Nov 7 Ct-Rye- (ct) -Ct (nt) β-glucosidse ctivity Phosphodiesterse ctivity d) July 5 e) Nov 5 f) 5 3 -Rye (nt) 1 rylsulftse ctivity -Rye (ct) -Ct (nt) Ct-Rye- (nt) Ct-Rye- (ct) Ct-Ct (ct) -Ct (ct) Ct-Rye- (ct) rylsulftse ctivity -Ct (ct) -Ct (nt) 1 Ct-Ct (ct) 1 -Rye (ct) -Rye (nt) Ct-Rye- (nt) -Rye (nt) 1 rylsulftse ctivity -Rye (ct) Nov 7 Ct-Rye- (ct) -Ct (ct) Ct-Rye- (nt) Ct-Ct (ct) -Ct (nt) 1 lkline Phosphomonoesterse ctivity Fig. f Three-dimensionl plots to investigte the seprtion mong drylnd cropping systems ccording to Es of C cycling (β-glucosidse, β-glucosminidse, nd α-glctosidse) nd P or S cycling (lkline phosphomonoesterse, phosphodiesterse, nd rylsulftse) in July 5, Nov 5, nd Nov 7. Continuous cotton (Ct Ct) under conventionl tillge (ct) from nery reserch site under the sme soil ws included in the comprison. The seprtion etween Ct nd Rye ws due to the significnt differences in these Es (P <.1) for ll smpling times, ut the seprtion etween Ct nd Ct Rye ws not significnt for Nov 7 (c, f) compred to forge or grin sorghum, rnging from. to 3 kg h 1 during the study; however, soil under the rottions with winter rye showed definite improvements on MN nd Es fter 3 yers. There ws decrese in soil Es under Ct Rye from July to Nov 5, which rnged from % to 1% depending on the enzyme (Fig. d). This ws not oserved in the other cropping systems, nd thus it could reflect chnge in microil community composition nd the production of enzymes or in the levels of extrcellulr enzymes due to chnges in sustrtes vilility under Ct Rye,which ws the only rottion smpled fter cotton in 5. The 3D plots for smples tken fter 5 yers (Nov 7) showed tht soil under Ct reched similr Es compred to Ct Rye (Fig. c, f) nd these properties were higher y 3% to 3% depending on the mesured enzyme ctivity compred to Ct Ct (Tle 3). This ws despite the lck of summer crops in 3 nd nd chnges in plnt iomss during the study. These findings cn indicte tht rottions of cotton with high-residueproducing crops (i.e., sorghum, corn), even without using winter cover crops, could lso e eneficil for improving soil qulity nd functioning (i.e., nutrient cycling, C sequestrtion) eyond 5 yers (Cusrno et l. ; Wright et l ). The chnges in Es s ffected y the cropping systems my reflect chnges in soil metolic functioning nd nutrient cycling tht re explined y shifts in the composition of soil microil communities (Kndeler et l. 199; Emmerling et l. ). For exmple, other studies in these cropping systems showed higher fungl/ cteril rtio nd higher cteril popultion densities of

13 iol Fertil Soils (11) 7: cteroidetes nd Proteocteri under Rye compred to cotton-sed cropping systems ( Ct nd Ct Rye ), which my explin the higher Es under Rye (cost- Mrtínez et l. 1). Shifts in the composition of soil microil communities increses the enzyme production tht my cuse n increse in the ccumulted enzyme tht persists in soil stilized into cly soil OM complexes over time (Nnnipieri et l. ). This enzyme pool my mintin the differences in Es mong cropping systems ( Rye > Ct nd Ct Rye >Ct Ct) regrdless of yers when the cropping sequence ws ffected, if the growing seson ws not possile, due to insufficient precipittion (Knight nd Dick ). lthough it is importnt to evlute severl Es s group to hve etter insights to the soil metolic cpcity s ffected y cropping systems, s to wht dt evlution tools re chosen in order to understnd ctul trends is crucil. For exmple, we lso used PC plots to evlute ll Es (six) s group (Fig. 5), ut they showed seprtion mong these drylnd cropping systems similr to the 3D plots for three relted Es t time (Fig. ). The PC plots did not provide dditionl informtion compred to the 3D plots, nd they cnnot revel the ctul Es xis (7.9%) xis (.%) Novemer xis 1 (9.7%) Rye(ct or nt) Novemer 7 Rye(nt) Rye(ct) Ct Rye (ct or nt) Ct Rye (ct) xis 1 (9.3%) Ct Ct (ct) Ct (ct or nt) Ct Rye (nt) Sr Ct(ct or nt) Ct Ct(ct) -Rye (ct) -Rye (nt) Ct-Rye- (ct) Ct-Rye- (nt) -Ct (ct) -Ct (nt) Ct-Ct (ct) Fig. 5 Principl component nlysis of ll Es (β-glucosidse, β- glucosminidse, α-glctosidse, lkline phosphomonoesterse, phosphodiesterse, nd rylsulftse) together fter 3 yers (Nov 5) nd 5 yers (Nov 7). The dt shown re the mens ± SEM for ech cropping system nd tillge comintion shown y the 3D plots. In ddition, the PC plot for the Nov 7 smpling (yer 5) showed seprtion of tillge tretments for some cropping systems tht should e tken with cution ecuse there were no significnt tillge effects in this study. For exmple, the seprtion due to tillge for Rye ws due to the higher ctivities of lkline phosphomonoesterse (13%) nd phosphodiesterse (17%) under nt compred to ct, ut the sme seprtion for Ct Rye ws due to the higher ctivities of β- glucosidse (9%) nd phosphodiesterse (7%) under ct thn nt (Fig. c, f). Correltion etween soil nd/or plnt properties The M showed positive nd significnt correltion with Es (r>., P<.5, n=) reinforcing our elief tht increses in M were followed y increses in enzyme synthesis in cropping systems with winter cover crops nd less frequency of cotton (dt not shown). Soil M nd Es were positively correlted to totl C or totl N (r>., P<.5, n=) in this sndy soil. Higher soil TC content ws detected under Rye compred to Ct despite tillge fter 5 yers (Nov 7), nd it ws similr in soil under Ct Rye nd Ct, ut these results were nticipted y M fter 3 yers only. However, it is importnt to recognize tht there my e lso chnges in soil OM qulity influenced y these cropping systems tht re not detected with totl C determintions. The detection fter 5 yers of differences in soil OM content under Rye compred to the other systems is surprising ecuse it hs een postulted tht chnges in soil OM occurs over longer time periods for soils with high OM (Powlson et l. 197). Positive significnt correltions were lso found etween plnt iomss with soil MC (r=.7, P<.1, n=), MN (r=., P<.1, n=), nd Es (r>., P<.1, n=). In ddition, the 7 soil smpling reveled positive correltion etween MC, MN, nd Es dt with cotton lint yields determined in when ll these systems were plced under cotton (r>. 3, P<.1, n=). This is n importnt finding s cotton yields were not significntly ffected y these cropping systems during the 5 yers of this study. These dt for this sndy soil under drylnd production indicted the potentil of these soil microil properties s erly indictors of crop yields. These findings prove tht soil microil communities re importnt fctors in soil fertility nd crop productivity. Conclusions This study demonstrted tht differences in M or Es re more ffected y crop rottion thn tillge mngement for this sndy soil under drylnd production in semirid

14 iol Fertil Soils (11) 7:55 7 region. fter only 3 yers, rottions including winter cover crops in yers, when precipittion nd ir temperture permitted the winter crop (e.g., Rye nd Ct Rye ), must hve provided higher nutrients in soil through plnt iomss return, which explins these fst increses in soil MN nd Es compred to Ct or Ct Ct. fter 5 yers, soil under Ct reched similr M nd Es compred to Ct Rye, nd these properties were higher compred to Ct Ct. These findings with M nd Es re regrded s positive impcts on key soil qulity prmeters relted to soil OM, nutrient cycling, nd C sequestrtion with lterntive cropping systems tht include history of winter cover crop nd/or rottions of cotton with high iomss crops such s sorghum for this region. cknowledgements The initition of this study in 3 ws possile due to the funding from the Oglll quifer Reserch Inititive in tht yer. This reserch ws lso supported y the griculturl Reserch Service under the GRCEnet Project. 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