'The experimental plots were tinder long-tetni cultiva tion before the experiment establishment in 1990. whereas the native pr.tirie, surrounding thc research ...
Soil & Water Management & Conservation
Cropping Intensity Impacts on Soil Aggregation and Carbon Sequestration in the Central Great Plains The isminant cr•oppieg e stem in the Cnti Great. Plains is conventissnai trIage ICC wi.tn.et wheat atheism LI—summer fallose We investigated the e.ffIat. of 15 ye of cropping intensities, fallow frequenei.es, and C I ( aOl seei .ie: is eceo;e-’.mee ,ii:e, A era’ atee; stale was r;:amte,t a lOOP tAme. CO. n 5;.: am. 2005. soil. samples were collected from the 0-to 5- and 5- to 15—cm d.epties in matmen; grass, native prairie, and cropping intensities (Ci) that included winter wheat, corn (& maps i..). prows millet (Pa’niems.m miliawum LI, Its pea 10 ;iss. -.;rP-so. L. anl ‘Ltmmter tallow ISa name sage a mpiel pros In a tetereflee scat tot Jeante’ ii SOil parameter’.. Ihe mist :e:m.mve top rotation. n;f’.amtlv isereased C setce’.tratia cesmnpreed :1 time other Cli whew fallow oeeur:ed 00cr mere lord tr, Legume presence tn the rotation did not improve SOC sequestration relative to slimmer fallow, Significant amounts of maeroagaregarrs were assoeiatrd with grms and ;ete:msisr croppinp compared smith the ect-itmor’. that n vIed f.Ilow Reduced telioss freqneta cropping signmfic.mntle increased soil P051 neat the ‘.uetdce compared ii ith 1sT wheat tallow. .\laeroaggregates eshibited a significant positive relationship with SOC and POM. A significant mmegative correlation was observed between rnmeroaggregates and POM, especially at 0- to 5-em depth. Overall, a positive effect of eoutinuous cropping and NT was observed on macroaggregate flirmarton and srahiliiation a’ well as SOC arid POM.
Maysoon M. Mikha* Joseph G Benjamin Merle F. Vigil David C Nielson USDA-ARS
Central (real
[Sal ns R seaft 0 Station 4O 35 (n. Rd. (0 Akron, CC 8(010
-.
Abbreviations: ACR, alternative crop rotation; (11, cropping intensity; CT consentional tillage; NT, no-till; POM particulate organic matter; SOC soil organic carbon; WCF. whear—corn-—fullow; \iCM. wheat—corn-—millet; \‘CCM F. wheat--corn —millet —fallow; \X’( - NiP, su-hcat-—rorir—m Him—pea; \\‘i-. wheat—-tallow; \N’SA, water -stable aggregates
osses of SOC in the Great Plains have been associated with nhlage and summer fallow managunent (Bow iii n ct -ii, 1999, H korson et al., 2002a,b) In this regon, nv-nt r is th most I mitin facto for crop produ non Folio n p nods c included in cropping svstcms to improne soil water storage for subsequr. nt crops. Peterson ct al. ç 1998) pointed out that a fallow period imprones the chin e ofh in mg sons an am 1 hi n t r du ing g arn fill, th reby mner asing c op ai Id; hon n a loss of SOC durmni f thom- is ltkelv to occur. fallow, in any cropping sequence, is a period of microbial actin itt md residue decomposition with no crop residue input. Cons ‘qu ntln, the a iii b’com a use ptibl to md ro ion nd SOC loss (Hahorson ct ai 200 a . 1 lime eonmbmation of sn-heat fallow with ( T further promotes SOC losses bee u e tillam4c ( S inc msc i sidue mi mg ith il and soil ‘r. 0 us, nshmh n han rca due d c omposi ion. ( i) d trots oil ag rmo a an c’.p sen p n iou in protected SOC to soil fauna, and ii; ins teases losses doe to smil erosion ,Blc ins rod Fm , 199 d; Bearu. ct ml 199 Pro nan t a]. 199 dopnng \ I nipro cs h cons my m f ii c do i h f ii a p mad t is suC y p
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(Nielsen et al., 2005), In addition to increasing soil water servation. NT increases surface SOC asa result of increased residue accumulation, less residue mixing, less oxidation. less soil disturbance, reduced soil temperature, proliferation o root growth and biological activity, and decreased risks of soil erosion (Blevinsani Frye, 1 9CR; Six ct aI., 19’)9. It has bceu documented that Ni soil’ have impros ed soil aggregation. C sequestration, and aggregate stabilit (Mikha and Rice, 2004; McVw eta],, 2006; Lhang et a!,, 2007), which results in increased water ingltration and resistance to wind and water erosion lhang er al., 200’(. Soil aggregation is uric of the im portant characteristics that mediates many soil chemical, physi cal, and biological propcrtiesand improves soil quality and sus tain.ibilitv, The stability of maeroaggrcgares >250-pm diam. is particularl responsive to changes in management prti liao er a],, 2006; Zibilske and Bradfird, 2007). The loss of macroag gregateoecluded organic matter is a primary source of C and nutrients lust as a result of cultivation Six et al., 2002; Mikh and Rice 2004; han et a].. 2006; Zibilskc and Bradhard. 200’). Smika and Wick’ (1968) documented that the use of NT in the Central Great Plains improved soil water conserva tion, which allows decreasing fallow frequency (two crops in 3 vr. Nielsen et al. 2005 also recognized that intensifying a cropping system is possible with NT management in the Great Plains region. Intensive cropping systems with reduced tillage and fewer [‘allows provide more residues, increase SOC content, and reduced potential for oll erosion (Halvorson er at, 2002a). Reduced fallow frequency with less soil disturbance in an NT system, relative to CTwheat—fallow, can produce more grain per unit of soil water (Nielsen er al., 2005) and leave more residues on the soil stirhice (Cantero-Martinez et al., 2006). Therefore the possibility for sequestering C in soil increases with intensive cropping systems (Peterson etal,, l998 and NT management. Previous research in the Great Plains emphasized the ef feet of different tillage practices and reduced fallow frcquenc on SOC content (Peterson et al., 1998; Bowman et al., 1999; 1-lalvorson et al., 2002a,b; MeVay et al., 2006), crop yield 1—lalvorson et al., 2002bt, and soil chemical properties (Mikha et al., 2006’L Recently Benjamin ct al. (2006 evaluated the ci” feet of SOC and soil aggregation on soil physical and hydraulic properties, but they were limited to two rotations and grass plots. Very little documentation from long-term studies exists that compares the combined etlicts 0 f reduced fallow frequency arid Table 1. Description of cropping intensity and crop sequence. The phases of each rotation were combined for analysis. Cropping inlensity’t
Cropping sequence:
0,5
\NF-..> WF VCF EV\. F\VC i’S \5iMF, CMF\\ vlF\\( F\\( 54 WCM, CMW, MWC, WCMIS CMPVV, 54CR c, PW si 1- The cropping intensity indicates the frequency of fallow in the rot.at;on. 4 Al I ‘tatinnwern in no ii r’scept wheat atloss ss hich cx as stnded nOr-ri—il ,oni ‘.:irc-ent’n.cace \\F_ ‘vht-a F. sits F. nit 54 nIei I’ wa. ii
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NT on soil aggregation, aggregate size distribution, and POM. Furthermore, few studies have been reported that have examined the relationship bctween aggregate size distribution and increas ing SO(Z and POM. Thus, the objectives of this study were to: (i) assess changes in aggregate size distriburion, SOC. and POM caused bc NT management and by reducing fallow frequencies: and n correlate changes in aggregate size distributions with changes in SOC and POM, Ihis study is diffrent from previous studies because it evaluates the long-term influence of cropping intensity in combination with NT management on soil quality soil i,,,rc,, tior Pi, ‘f\f md C s quc ti ire n in p ir onctcr the upper 15 em of the soil in the Central Great Plains.
MATERIAL.S AND METHODS Site Description The research plots are located at the USDA-ARS Central Great Plains Research Station (Akron, CO) on the Alternative Crop Rotation ACR study sure The study lies at ‘iii. 1 lion of the station is I 38-i m above ine.ul
and 103.15 W. The dcvi-
level. Ihe research station is within a semiarid climate with approximately 420 mm of annual pre cipitation. Long-term sveather data show that normally about 80% of the annu.il precipitation occurs between April and September. About sea
2 S°o of the annual precipitation is receis ed as snow and another 29% oc curs as rain inJulv and August, a critical period for annual summer crop development. ‘The average daily temperature is 9CC, ranging from —2CC in January to 23—C miiJulv. ‘[he coii is aWeld silt loam a fine, smeetitie, mesic Aridie Paleustoll). The soil bulk density ranged from 1.30 to 1,50 gem 5 in the 0- to 15-cm depth. Soil texture ranged from 37 to 39% sand, 39 to 41% silt, and 22 to 23% Clay in the 0-to ‘75-cm depth. The ACR plots were initiated in 1990 under various degrees ofCI. Rotations of crops suited for drvland crop production in the Central Great Plains are the experimental treatments. Each phase of each ro tation was included in each year of the study, [he dii%rent cropping sequences evaluated in this study ire specified em Lible 1. The crop rota tions were comprised ofwmntrr wheat, u,rn, proso millet, and dry pea, with or without fallow. The crop rotations were compared with peren ni,sl grass plots, which were included within the experimental design. A prairie site was also s.unpled to provide a benchmark reference of’ soil properties. ‘The experimental plots were tinder long-tetni cultiva tion before the experiment establishment in 1990. whereas the native pr.tirie, surrounding thc research plots. hi.is never been cultis-atrd. The experiment is organized .n a rnidomiied complete block design with three replications. Because the native pi an ie was not replicated within the experimental plots, it svas excluded from the statistical analysis. One crop was h,srvcsted from the wheat—fallow (WJ’ rotation every 2 sr (0.5 CI : .i crop wSx harxsts-d from the wheat—corn-. fillosv \\‘CF rotations 2 our nO r 0.6’ CI); a crop sri’ harvested from the wheat—corn--mil let—fallow (WCMF) rotations 3 out of •4 yr (0’7S CI); and a crop svas harvested from the wheat--corn ---.‘niilet WCM’ .snd the wheat-cornin TIer-pea SVCSIP rot,stions ever5 sear I it Cl 7 She perennlal grass plots were originally seeded to a mixture of -45% smooth brome i4romm
lee-mis Leyss), 45% pubescent wheatgrass [4sropyroii trichophcirum l.ink K. Rieht,,snd 10’ alf,slt.i Mi,/,’,an ‘,tfict L, at the start ut’ lie experi incur. lIst aif.slia quields died. so by the rinse the samples were
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taken (2005), the plots were almost exclusively grass. The native prai tie site mis a mixtute o blur grama Bsut/on.i )Kunth I ag. flirt and nutialo irr ass Imrc/ilrei Lur ion-Irs Nutt. (.‘umbus Soil was sampled from the rxpcrimental plots, including the grass piots.
WSA were evaluated using the procedure reported by Mikha and Rice (200-i). Aggregates from etch treatments sveme separated into macro aggregate r> 100(1. 500— 1000, .uud 250—500 p to md tnicroaggrrs,ate (53-250 and 20—iS pm) siCe fractions,
and from three locations in the prairie rite, The three native prairie Inca rions s-ic rarh within 100 n south, cast, and west of’rhe dpc ofACR
Particulate Organic Matter
espcrirw iii plots .Nati vii
ra tie v,tllrs
cur
included
ri
provide a
benchmark teCrence of soil properties. No-till management was used on all rotation plots except lilt the 1 th \ I ‘l r tan i i— hi Ia n a i L, I i ii I I CT lilt \\‘E- rotation ncluded tiliage orb three to six sweep plow operations approximately 8 to 10 cm deep as needed for weed control during the summer fallow The plot size (9,1 us by 30,5 m) .ird na hiriert working widths were h that the wheel tracks lot field operations fhhlow a controlled o heel traffic pattern. 1h’ tank soil distur bance in untracked areas was from planting operations. In the NT plots, chemical weed control was used during the fallow and cropping seasons. A typical herbicide application scheme consisted ofa residual herbit. id application of atrazine [(‘-cltloto-A-cthvl-A’ ‘-i, 1 -methvletlsvl)- 1,3.5. triazine-2,4-diamine] alice wheat harvest. A burn-down application of glvphosate (isopropylamine salt of A’-(phosphonomethyl)glvcinej was applsed shortl hckerc planting the billowing crop. Several glvphosate applications were made, as needed, during the billow period tke weed control. Wheat planting occurred in mid to late September of each year of the study. Corn planting occurred in mid to late May. Millet planting
-
Particul,nc organic i outer St a ‘determined using the procedure ta f Cam bardella etal. (2001). line fly, 30 g ofsur-dry soil was dispersed in 90 mL of 551 sodium hexametaphosphate. The susprn.sions we.re shaken fir 16 lx on a reciprocal shaker. ‘[ht d ist’.crrcd soil Wa’ passod through .u set of nested sieves say i etneshsizesof 11)00, S0 250. and S pun. is lienci the imtaterial retained on each sieve was rinsed until all materials smaller than the mesh size bad been washed through. The material retained on e,ucb sieve t.t’.us transferred ito an .ihuimtiiun weighing Pan and dried to .u constant weight at 50’C. ‘The dried mass was recorded to the uue,urest milligram, Loss’on’ignition for POM was determined by the mass dif ference after -I bin a muffle furnace ,ut 450’C. The sum ofdiffkrent POM size frictions to tal POM was used to evaluate tIle etfrct of different Cl and tillage on soul POM content. In ,iddution the individual POM size fractions were used to evaluate the relationship between WSA and P051 within the same size class. The P051 was calculated as reported by Mikha et al. 2006) sinai g ))u4,)
situ
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occurred in lair Slav or early lime. Pea planting occurred in early April. \\‘heat, millet, and pea were planted with a 0.1 9-m row spacing and corn
planted with a 0,76-m row spacing. Fertilizer N was applied to each plot according to soil tests obtained each year and the projected crop yield. The N source was NH NO . broadcast before planting the crop 5 or as a dribble band “16 cm to the side of the seed row as a 32°c N solu’ lion of 5 NO Foe wheat only, a starter fertilizer of 11—s2--0 4 urea—NH , (N—P--K was b,inded with the seed at planting at a rate of 2.8 kg P ha Soil samples were taken in MarcIa 2005. which wa, 15 yr after the establishment of the ACR research plots. Samples svere also taken from the undisturbed native prairie site, Composite samples consisting of 10 2.5-cm.diam, cores svere taken from the 0-to 5’ and 5- to I5’cm depths of each treatment using an C)aktield soil probe’, Forestry Supplies. Jackson, MS). Soil samples writ collected betsx ecu the ross’ from each plot. Wheel-trafficked areas were purposely avoided during sampling. Soil samples were placed in sterile polypropylene bags. kept in coolers during field sampling, and stored at 4(7 ,iftcr collection. The held-mr ii soil samples were ptesievcd (6- mm diam. befilte seem neving to remus e stones and coarse organic matter, to homogenize the sample, and to de fine Tic irisi linen ii for b . ui,r i. rs, o hr. 1 ‘roil Ia uk den ri determined concut i ends fia ‘m cole sanuple taken at the it- to 5- md 5- to li-cm depths ole itch treatment (,rossinaiu and Reinscb. 2002
Aggregate Size Distributions
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Fifteen ‘ears after initiation of this study, the soil p1—I in the plots ranged from ‘iS to 5.82 within the 0’ to S-cm depth md freon 5 I to 6.12 fir the 5. to 1 S-ens depth. Low soi 1s 1-1 (1000 pm 5- Sot.’— I 000 urn
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Fig. 2. Sand-free water-stable aggregates in different size fractions within the 0- to 5-cm depth as microaggregates in cropland. affected by different cropping intensities (W, wheat; 1 fallow; C, corn; M, millet, P pea) and tillage (CT) Soil POM was signif1cantlv in conventional tillage; NT, no-till). Lowercase letters represent significant differences (P 1000 and 500—1000 pm) at both depths (Fig. 4A 1 cropping rotation WCM signieant1y increased soil POM at the and 4A,). For 0- to 5-em, the slope of the regression line was 0- to 5-em depth compared with the other continuous cropping significantly (P = 0.Oa) greater with the smaller maeroaggregates rotation (‘sX-CMP) by 1’°o and continuous grass b 21%. Soil than with the larger size inaeroaggregates (Fig. 4A ). Also, fin’ 1 P(.)M associated with 1.0 CI (WCM) was signicantly greater the same amount of soil organic matter (SOM), the amount and than the rotations containing fallow, th 0.50 CI (W-F\T), 0.6 stability of the smaller maeroaggregates were significantly greater Cl (WCF), and 0.”S CI (WCMF) b 53. 29. and 21%, respec than 0 w the larger macroaggregates. The greater mass of small tively. This indicates that, in general, the differences in soil POM macroaggrcgates (250—500 i.im) than larger macroaggregates among CI increased as fallow frequency increased in rotations. could partly he due to the disintegration oflarge macroaggregates This observation is consistent with Mikha et ,il. (2006:. who ob (>1000 and 500—1000 )im) induced by slaking. It has been well served an increase in soil POM les ci with a reduction in tillagc intensity and fallow frequency. Numerically, 0-Scm [EEl S-lScn’ the PONI measured in the adjacent reference native prairie sites were 2.4 times greater than the highest values measured in the continuously cropped rotation plots.
Relation between Soil Aggregates, Soil Organic Matter, and Particulate Organic Matter
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Fig. 4. Relationship between sand-free water-stable aggregates (WSA) and whole-soil organic C (Mg C ha© as affected by different cropping intensities and tillage within the 0- to 5-cm depth for (A ) macroaggregates and (B) microaggregates, and the 5- to 15-cm depth for 1 (A,) macroaggregates and (83) microaggregates. The regression lines for A 1 and A 2 group large macroaggregates (>1000 and 500—1000 pm) fractions together for analysis, where different symbols identify each aggregate size class. The symbols that are circled represent the relationship between sand-free WSA and Soc from soils collected at the reference prairie site and are included for reference purposes only. The prairie data were not included in the regression analysis.
documented that come large macroaggregates often consist of clusters of small macroaggregates and inicroaggregates (Jastrow and Miller, l99; Six et aL, 2000). As the macroaggregatcs in crease in size, they become more susceptible to disintegration due to land use management (Jastrow and Miller. 1997; Six et al., 1999, 2000 arid slaking (Tisdall and Oades, 1952). Indeed, as SOC increased, the stability of smaller macroaggregates in creased significantly and at a faster rate than the stability of the larger n acroaggregates (>1000 and 5(0-- 1000 pm). In the 5— to 15-cm layer. the slope of the regression line for the smaller mac roaggregates was not significantly diulirent than for the larger mnacroaggregates( Fig. 4A ). 2 Low coeflcients of determination (0.05—0.3) and nonsig nihcant relationships were observed between SOC and microag gregates (Fig. 4B 1 and all,) at both depths. This indicates that thc amount of microaggrcgatcs measured was not related to the SOC amount. Previousk, Oadcs and \‘Citers 199 i. jastrosv and Miller (199’). and Six et at (2000) reported that rnacroag gregares ire comprised of clusters of microaggrcgatcs. Thus. in creasing macroaggrcgare stability with increasing SOM leads to reduced macroaggrc gate disintegration and increased microag grcg.src protection within macroaggregates Oadcs and Waters. 1991; Jastrow and Miller. 1997; Six et al., 2(100’. The prairie samples were not included in the regression analysis because the prairie site was not replicated and bee.susc the higher SOC val ues ofthe prairie samples would have resulted in a discontinuous data set.
.SSSAJ: Volume 74: Number S • September—October 2010
Th further elucidate the effect of SOM on individual ag gregate size fractions as- aectcd by different land management (CI and grassland), the relationship between WSA and POM within the same size class was evaluated Fig. 5). lhc relation ship between WSA and POM was affisctcd by aggregate size class and soil depth (Fig. 5). Similar to the relationship between SOC and WSA, there appeared to be a positive linear correlation (Fig. 5) betsvcen POM and soil macroaggregates (>1000, 500—1000, and 250—500 pm) ;vithin both depths studied (0—5 and 5—IS cm). This indicates an increase in soil maeroaggrcgates as the soil POM of the same size class increases. The [nactoaggregate sta bility was significantly and highly correlated with POM at the 0- to S-cm depth but not at the 5- to 15-cm depth. The 0- to S-em depth had a greater concentration of POM than the 5- to 15-cm depth and this may explain the stronger relationship. A negative correlation was observed between PO_\l and nucroag gregates Jig. 5, which was significant (or the 0- to 5-cm depth but nor for the 5- to 15-cm depth. The prairie data are included as a rc[ercncc point for hon the relationship bctwci. n WSA and POM changes with cultivation.
CONCLUSIONS Fifteen years of continuous cropping signiflc.ootlv increased macroaggregares and POM relative to the \\l—( --i— arid to rotations. The presence of pea in continuous cropping systems did not in3pros e SOC relative to cropping systems that included a fallosv period. The significantly greater amount of soil micro cgrgorv 1000 00 1000 md 25— >00 I m di sin’ SOC. soil
1717
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l’arOeulate organic matter g POM kgd soil) Fig. Relationships between sand-free waler-stable aggregates (WSA) and particulate organic matter (POM) are compared within each individual size fraction at (A) 0- to 5- and (II) 5- to 1 5-cm depths as affected by different cropping intensities and tllage. The circled symbols represent the relationship between sand-free WSA and POM from soils collected at the reference prairie site and are included for reference purposes only. The prairie data were not included in the regression analysis. •
associated with \\-F\. . compared with \\‘F_ 1 . seas a eonseelucnce 1 of tillage elimination. Reduced tallow Fre,.juencv significantly in creased soil POM at 0 to 5 cm compared with 0.5 Cl cWFCT and WFNT). The folly cropped WCM rotation significantly in creased POM, especially within the 0- tI I s-cm depth, compared with the other cropping systems and grass. Macroaggregates cx hhitcd a signihcant. positive relationship with SOC and POM. whereas the microaggregates had a nonsignificant relationship with SOC and POM. Changes in soil properties and SOC in the Centr.d Great Plains appeared to he slow doe to the dry condi’ and loss’ hicmass production. Crop rotations that include a fillow pertod ar tiliage promoted SOC losses, thus slowing SOC accomi,ilation and aggregate formation. Jo improve soil produc tivity and susrainabilirv, it would be beneficial to identify the most suitable rotations for Ni’ cropping systems in the Central Great Plains.
1718
ACKNOWLEDGMENTS publiration is based on work supported hr the Agricultural Rescard, Service and recently partially supported under the ARS CRACI:net Project.
This
REFERENCES Orate. NIH., RI. Hen Ins, and I).)’. Coleman 199”i. \Vtter-stahic aggrecates md .,anic ernie, Rarrn’n, 1 ,,sri,t,o,,ai md ml. Soil V. Sw. An,. I.
lie,,,ammn. (., \i.Ni. Nl,kha. and NI.). \,l, 10(15. 5 ),ean,j jarbo,, mr ao,l ph ‘oral and drauiic plOperties fl a Semia id dimare. Soil Sei, Sw. Am.J..7201357—1362. Baneo-Canqm, H., MM. Miller. [C. Ben amin, LII. Stone, Al. Sehiegd, 1 1)1 I.e’ NI I. N Cei. and INS Stahinem. 2(519. R eional studs sf ns,n!l mpacer (1 tea, -uttare atgrcgare props-its> that ,I(tl(,ence s’d crod,b,l:ie. ,,,
S,i 5>. Sw. An. I. 361 -1 Bier us, R.L. md \V2S, 1, se, 1993. Co,,sersat,on tillage .\n ecological approach
to soil management. Adv, Agom.. 5033— 78. Boss man, R.A .10.0 Vigil, D.C. Nielsen, and 0 L. Anderson. 1999. Soil orgtnic matter ehangee ni , ts,(flssls cropped d sland ssst,-ms, Soil 5>. Sac:. An,, 50-191. (.5 A NI. (;aCda. INN Djeao. 113 \Nocsc:,d. md [.5. Ketilci. (01 1 mao, nt pate and rot., organ i matter ha ‘a might It’>
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SSSAJ: Volume 74: Number 3 • September—October 2010
omignition. p. 349—359. In R. Lal et al. (ed, Assessment iwth sit for soil carbon. CRC Press, Boca Raron, FL. c: ftc. ‘cfail, L.A. Shed, arid C A. I’erm on, 200o laing-terin crop esidue ci VHS iicsit, no- till roppmrz ,u,reins tinder rtiii rid c idicins I. Soil SMart Ci’,c’ri t I S-i—OS. t. iek, LU and MG. Gluier. 1995. 1 ninared soil organic arhon losses irons ksnor-m crop’faliow in the northern Great Plains ot the USA. p. 85—92. hr R. Gil et al, (ed,) S-oil nianagensent and greenhouse rICer. Ads’, Soil .Sci. Set CRC Press. Roe Raisin. FL, G:.msan. RIG and LG. RsaGic. ooz. IGis’ld phase p h’i -225. Pci Li. I )aiir ml (;.C. ‘rd SIthd .sI’soil .ieaGiis Part -i. S”sA Book Me. S. 555.5. Mactoo ii, Ha.is’csrsoo.,A.,D., G.A. Peterson, and CA. Reule. 2002a, Village ssr.ena and crc-p rotatios effects on dryland crop Geld and soil carbon iii rhe Central Great Gin’ Agcoii.i. On: I .‘9 I aSh. I )alss,rscciyA.i”) H.!. \Vsenhrsld. and -S.F. Black Si.SUE. I lla5e. uitr”yrri. mci crompi 15 s’.’-,trmmcs elliot’ itt soIl cal hon seqmlc’ctratit’n. Soil Sri, Soc. Ani. I. 66906—9I2. Hats, HI,, WV). Willis, and Jj, Bond, l9hn. Suinniet billow in the northern Great Plains spring whe,it), p. I —45. /n Summer billow in the western United States. C,nsrrs Res. Pep. L’. Us. m’t. Print, Ctlfiee. \‘Gishitigtotm, l)C. Jastrose, J I ).. :nsl R. H. Millet I 092, Soil aggreg.ite ,tsbihi,mtjc,n aim) ear’bmn sequestr.ition: F eedbaeks through o:’ganoinnieral associations. p. 209— 223. In R. Lal et ai. (ed.) Soil processes and carbon cycle. CRC Press, Boot Raton, FL. Jim, 1,, TL. Whalen and \MH. Hrndersliot. 201)6. \ms.-tillage and manure applie.irii’n increase aggregation and impross- murrietit retention tm .i sandyloam sill. (iei,dertmia I /-.2-t— 33. John, B., T, Yamashita, B. Ludwig, and H. Flessa. 2005. Storage oforganie carbon in aggregate and density fractions of silty soils tinder different types of land use, Geoderma I MeMo. L.A., J.A. Budde. K. Fabrizzi. MM. Mikita, CAM. Rice. Al. Sehlegd, lit. Peterson, 11AM. Siveetmey, mud C. Thompson. 2006. Slati.mgemenr elkets on soil phi sir.ml properties mt ong.terin ttllage stndies mi Kansas. Soil Sci. Soc Am,J. 0:434—’i38. Mikha, MM., and CAM Rice, 2004. Tillage and manure effects out soil and .mggregatc.assocmatrd carbon and nitrogen. Soil Sci. Soc. Am. J. 682(09—816. ilikha. MM.. CAM. Rice. and GA Nliliiketm. 2005. (‘,trbon and nmttngemm mnitmeralizariomi is ,illhried by shying md ss’ettimigrveles. Semil Hint. Biocbettt. 37:339—InS. .
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Mikha, MM., ME, Vigil, M,A. Liebig, R.A. Btswniami, B. MrConkes. E,J, Deibert, and J.L. PAul, Jr. 2006. Cropping system influences on soil chemical properties and srsil qu.ilirv in the Great P1.615 , Renewable Agric. 5 loud -Svst. S ISo’. $5. \iirlsc’n, D.c iSs\ Unger. mud PR. Si/let. 5005. ElIi,,ieitt starer use in ci: and cropping stiti,lfls 10 the (.meat Puns, Agu on. J. 9’S 364.—V’S. Oades,J,M., and A.G. Witers, l99 I. Aggregate hierarchy in soil, Ause.J, Miii Res, 29G15.-828. Paucni.mr. K. H P iS’llisc. rid E..\ PatsI. I’M”. Mait.ugeiient o’iitl’Os 01 i cml bun. p 1 —tO. IS F .5. Paul et ,ii. ed St mreamiie in:mttsr ii tcrm1’c:,mtc 5 -igrsmec’scsvstcmns. Ling 55:10 csprruisnirnns us No:’th ,\luu.:lc.m. (.RC S’ss. ,i Ratcin, FL. 5 I3o Peterson, GA., AD. Hhivorson, J.L. Havlin, OR. jsnes, D.j. Locn, a.nd. DL. Tanaka, 1995 Reduced tiliage and incrc.ising cropping intensim irs the I I i t ( “ i Li I), a (i”_ I Russck. -S.F.. [1.5. turd. LB. P,irkui, ,innci -S P Si ills inip:iuu Pc itiruusgmsus ferlul oration md cesuppulg 5 cstein on s-triton scs ucsti Shot I I ri 1 midwestern Mollisols, Scnil Sei. Soc. Am. I, 69:4l3-n22, SAIl Institute, 1999. SAS/STAT user’s guide, VersionS. SAS Inst., Cary, NC’. s. T., It. F. Elliott mud K. Parstian. 1999, Ar,grcgarmt mud scsil organic matter dsmu,tmmcs under eouis’etittm,umal mud no-u/laCe svsteiums. Soul Set. ‘Soc. ;nm. I. 63 I S0— ISiS. Six, J,, 1-.. I’. Elliott. and K. l’.tusriani .2000, Soul macroaggregate ruenosct and microaggregate forniartots: A mechanism fcur C sequesrraricsn under no rill.mge agriculture. Soil iliol, Bic,ehetn, 32-2099.0103. Six. I.. C. Feller. K. Denefl SM, Ogle, J.C. Mot,ars Sm ,,mmid ASIc trOt. 2)102. Soil mirg,mumie flatter, btsita mttd .mggregatiomi ti temperate attd tropical soils: 1 is olttum tiIl.mge. Agru’mnotsmie 52C55-—’”S. Elk Smika, [‘1.12., aitsl (IA, Wicks. 1968 Soil water storage during fallow in the Cetitral Great Plaitis as influetseed by tillage atid herbicide treatments, ScOl Sci. Sue, Atti. Proc. 32:591—595. ‘Fisd.tll, FM., ansi TM. HOes. I 9s2. (‘irgattic timarrer mud ii art st.mble aggregates itt soil. J Soil Si.33:I-al—I6I. Zhauig, G.S., KY. Chats, A. t.)ates. l).P. Heenan, and GB. Hu,mng, 2l1tM. Relationship between soil structure and runoff/soil loss after 24 years of eons enriotsal rillage. Soil Tillage Ret. 92 122—128. Zibilskr, GM.. and TM. Bradford. 200’S Soil aggregatiomi. aggregate carbon mmmd miittogett. amid rmmoistnre retentiotu itiduced Its eoetset vatintt ttll.tge. Soil Set. Soc. Am. J, I ‘S93—802. ...
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