Chapter 2

Impacts of Soil Organic Carbonon Soil Physical BehaviorHumberto BlancoCanqui arid Joe Benjamin

Abstract

Managementinduced changes in soil organic carbon fSOC concentrationcan affect sol physical behavior. Specficaliy, removal of crop residues as biofuel may thus adversely affect soil attributes by reducing SOC concentrationas crop residues are the maln source of SOC. Implications of crop residuemanagement for soil erosion control, water conservation, nutrient cycling,and global C cycle have been discussed, but the potential mpacts of residueremovalinduced depletion of SOC on soil physical properties have not beenwidely studied. We reviewed published information on the relationships ofOC orcentatior vth ou stuctt r& stabmt consistecv compac4’cnsoil water repellency, and hydraulic properties with emphasis on crop resndue management. Our review indicates that studies specifically assessingrelationships between crop residue managementdnduced changes in SOCconcentration and soil physical properties are few. These studies indicate,however, that crop removal or addition can alter SOC concentration and concomitantly affect soil physical attributes with a magnitude depending on theamount of residue removed or returned, constituents of residuederivedSOC. tillage and cropping system, soil type, and climate. Our review also indicates that, in general, management practices that effect Soc concentrationcan directly influence soil physical properties. Decrease in SOC concentrationreduces subcritical water repellency arid aggregate stability and strength,increases soil’s susceptibility to excessive compaction, and reduces macro-porosity, hydraulic conductivity, and water retention. Soil organic matterimproves soil physical properties by providing organic binding agents, induclog slight water repellency, lowering soil bulk density, and improvmg the&ast t1 ad e I ece o’ h F ce o’ e memus ners c’ OCsoil physical attributes suggest that crop residues should be returned to soilto maintain or increase SOC concentration. Indiscriminate residue removalfor offrfarm uses reduces SOC pools and can adversely affect coil and envronment. Crop residues not, only protect the soil surface from erosive forcesbut also maintain SOC concentration, which is essential to improve s..oil physical behavior and sustain soil orodtjctivity Management cractices includingco nil .0th residue return, continuous cropping systems, cover croos andgra . eta citd000s rru c oe rurNoteta 0 It. the c ase sOC cncertra.tion and thus improve soil physical behavior.

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0 2013. OSSA, SSSA. 558°. GuSford O1 r- 55r55 usa.Quanttfyirsg and :‘nodedng sod structure dynamics. Sally Logsdon, Mrkus Behi. and miner Horn led.)Adeances in Agricultural Systems Modeling 5cr c-s 3.

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crop reiduc emo’ ii ‘r iciditi n site r the oi eentr ate n torganrc C in the soil. The cha npes in SOP ncentratjon may

con.conutanti impact soil phyvical i. ttributes and soil producti.vity. Soil organicarticles interact n th inor anic particles to nn’mnte i)JJ a’4arepYatinn, n,c.reace

porosity, and stabilize soil structure (Kay; 19W). Influence of soil organic matter

on soIl 5.tructure, nutrient cc1mg, C cyclirg, soil biological processes, and otherens’ ct m w rw cc P r ti hei A and ctao hft A 4 F tk C

nisms involved and the magnitude at which :manaement-induced changes inSOC influence soil physical properties deserve further discussion.

Specifically, crop residue removal or addition dictates C input and SOCdvnamws At present, crop residues are confronted by a number of competing omand off- farm uses. Cn on.e. .han.d, crop residues are need.ed to conserve soil andwater, reduce water and wind erosion, and maintain 5CC concentration (Ailhelrnet aS. 2004). On the o.ther hand, residues have potential offifarm uses includingcellulosic ethanol production (Perlack et aS, 2005) hher production (Reddy andYang, 2005), and livestock feed (Tanaka et al., 2005).

Influence of residue-management-induced SOC gains or losses on soilphysical behavior such as structural stability, compactibilty; and soil-waterrelationships has not been widely documented, Changes in s:oil physicalproperties and SOC concentration. in. re.sidue naan.agement studies have oftenbeen discussed as static or separate parameters with little errph.asis on the mutualinterrelationships between soil structure and SOC. A synthesis of information onSOC vs. soil physical behavior relationships is needed to better understand theimplications that crop residue management m.a.y have on. soil physical properties.Co rreiat:ions between. soils truct.ural properties no 5(i( concen.trati.on 0.avcreported, but inisirmahon is frassmented. anci. h.as not teen .resented in a comnac.mf:r.rr.ess’ ork. a.ppl.i.e.u to crop residue m..a r.agemert.

Ther.vfore. the snecific abiective of this caaote.r is to discuss the reIE.itionsflipsof SOC with soil structural s:tabihty, con.sistency, compaction, soil wa.ter n.tpellenc.y.and hwirau lic properties based cn ublisb.ed stodi.es .vitl5, phas.ic .n cr0 presidue managemen.t. We revicnved (I) published studies, which assessed theindependent effects of cr011 residue management on soil physical properties andSOC concentration and (ii) relevant studies reporting information on SOC vs. soil

13

fropacts of SoU Organk Carbon on SO Fhysic& Sehavor

pnJperties deserve discussion to bettr.r uric.erstand interactions and soiPspacificra.sponse to crop resid.ue manazement.

FACTORS THAT AFFECT RELATIOHSHIPS BETWEEN ORGANIC CARBONAND SOIL PHYSICAL PROPERTIESThe xtent at which c.haniie.s in soc concentration a.ect soil physical propertiesdepends on various interacting factors in.cluding climatic corditions, amount anconsthuen[s ot SOC testura Jas. tillace management. and thers iFig, 20. Forexa.mpie, cli.mate in inte ractiort with tillage ard cropping systems directly influrrnces crop residue production and rates of soil orcanic matter decomposition(Benjamin et iL, 200 :), Fhe numerous ir1toracting factors make the charactorizahon of SOC influence on. soil physical and hydraulic properties somewhat difficult.

Amount and Constituents of Soil Organic CarbonBoth aniouot and form c t SOC influence soil physical behavior. A narrow range

t i sem-at is t nron nt s wn n a dueedor no effects on soil phyical properties. l.n the central Great Piains correlation

Fig. 24, Factors and interactions that influence relationships of soil organic C concentration withsol structural, compaction. consistency, mechanical, and hydraulic properties

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Fig. 2-2. Relationship of added crop residue C plus estimated added root and rhizodeposition C(C ) on changes in soil organic C (SOC) in the 0 to 30 cm depth increment between 2001 and2008. NT denotes the noulli cropping system. The CP denotes the chisel plow cropping system.CC denotes the continuous corn rotation, Rot denotes the mixed grass and broadleaf crop rotadon, (From Benjamiii et al,, 2010).

.1Ioa.rn i..n the entral Creat Piixl..ns, there was n.o signiheant correlation between

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2t1- t.o 37-cm oepth, macroa.ggregates were positively correl.ate.d, although weaklysoth differeocen ).O SOC cooentratun across orooping system; with )vrentamounts of annu.ai bi.omass C input (henamin e.t aS, 3058). Oifferences in root

7aern5 and intenictions ho twc.en soc and ml so fractions mao a liectSoil gregation at deeper depths. Further assessment P SOC 05. soil structurerelahon.ships for the whole sod profile is; needed to understand how d.ifferentscena nos of crop residue management in tluence soil properties.

Tillage also affEcts the na.ture and partitioning of organic binding.: a.gents thatS4regatr n ad mak 4it mU r itm 37 i rt IL w w r rr

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!mpacts of Soil 0rgnic Carbon on Soil Physical behavior 21

ration promotes aggregation, reduces soil compactifility, and improves soilhdraulic propertiet... On the ot.her hand, improved soil slructu ra•.l properties promote hOC preteotion and storu’e, hoji i essontal to lontoterm C seauestrat,una.m. overall soil productivi.ty. The s.pecifi.c relatiunships of SOC with soil physioropertios are discussed in the Ollowin ntionS.

EFFECT OF ORGANIC CARBON ON SOIL WATER REPELLENCYCropoesdue derived SC may induce some hd ruphobic proportion to soil Thbk’2i). While excessive soil water repellency ca.n adversely affect soil structurevid I dro1og a rr t al 100( MaDor ild nd F Tuff van 2003i s1 ht srepellency observed in cultivated s ils can have positive impacts or aggregate stahilization and long4erm C sequestration (Hailett et oh, 2001; Eynard et oh, 2006;[,amparter et al., 2009). Residues are a food source for decornposers including earth

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into raction between clay content and SOC concentration most probablyi.ncreasrsw. it h.vdrophobicitv in clavuy soils over clay or SoC concentration alone.Assoc.iation of SOC or humic with clay nyneah ha been found to

we h d b it mJ iL( h w t 1 2 1 Z d IUc \ICret aL, 2007). ,Particu larly, recalcitrant SOC fractions associate vi ith the finest claytmctions and induce high hvdrophohictv (Soaccini of a!., 2002). Predornjnantfactors that influence the manifestation of soil water repellency include SOC, cia.,concentration, and coil matric øo tential (Ce lunge et a!.. 2007; BlancoCanqui andLal. 2008b1.

increase in SOC concentration with intensive cropping systems with highresidue in.put als.o increases water repelle]rcy Continuous cropping systems withconservation tiiiage hich leave residues on the soil surface, can accumulateFtC near the soil surface and induce water repellency to soils. a 3.3vrcropping system e\perment in the central Great Plains, continuous wheat had5 times greater aggregate water repellency than the average across sorghumfallow, wheahsorghum [Sorghum b/color (Li MoenchffaIiow, continuous sorghum,and who atfta How under nmtill for the 0 to 2.Swm soil depth iBlancrvCanqui etal,, 20’lOay The hvdrophobicitv of residuederived SOC varies with the quality ofcrop residues. Ce Jonge et al. (2007) observed that soils under barley and potatoes(Sotanum tuberosum Li had slightly greater soil water repellency than those underroe (Scrub cop-eat L., wheat, and corn. They also observed that grass plots hadconsistently greater soil water repellency tha.n croppod systems at all soil watercontents. Overall, changes in SOC concentration with residue removal or additionma chrne the hydrophohicity rf soil dependl04 on the uuartth and qualite ofrcSjdues. More eiperimenta! data on the impacts of crop residue management onsoil water repellency are needed.

EFFEcT OF ORGANIC CARBON ON SOIL STRUCTURALSTABILITY AND STRENGTH1nfluenc of ,.,,,:,,.,,,,ic matter on cii aggrecation has been ‘videl iiscussed (Ticd all and.. Oadeg, 1982; Cha.ney and Swift, 1964; ft/oil and Ma.gdoft, 2004; Fig. 2.-4),hut discussion. on the specific impacts of crop residue removal or addition on SOCvs. n)il structure rel.aeimsships is somewhat limited (Table 20). Crop rvsidu.es maydiffer on their impacts on soil structure from other amondnsents (‘e.g. animalmanure, sawdust, and compos;t as SOC i.nfluences on. soil. structure depend onhe F. pe and qualitt of um ndmt nts (Bhngl t i 20’bb L t OC n th

due removal n.a have a. greater im pact on soil structura.i parameters such asaggregate stahlitv and strength than o.n other soil physical properties (Sparrowet al.. 2006).

residue management., wheat and sorphun. residue removal from irrigated andI md I r d Uc d t H’ r t. it r i o rt mand SOC concentration from 5 to e45 g kg’ ihordovskv et a!Application ot crop residues h.as the opposite effect to residue removal

because it increases SOC concentration and. it thus improves aggregate stahi !i.ty.On a silt koam in Ohio. increase in SOC concentration wa i nearly related is

to the tncrewe In percentage ot waterwtahie aggregates in the . to 1°cmdepth a.fter a Ayr wheat straw applica.tion at five different rates to not.i.ll, plowtill,arid r idge’tili soils (0uiker and Sal, •‘l999 On a loam in Spain an increase i.n SOConcentration with the application of wheat straw at five different levels increased0 ‘t ihilit plvniri r ib f in 1 iv tilt ii tr

‘.lOsom depth in a r study (Jordan et al., 2010,). Addition of hvproduct:s of cornstover fermentation can also increase soil aggregate stability by increasin.g. SOCconcentration. Johnson et a!, (201.4) reported that addition of stover fermentationo pr ou in’ 4so kg ot 0C s ne 0011100 I1n1rl\ wd me ‘u gaostability, explaining 98” of its variability.

The main mechan.isms by which crop residue removal reduces the stability of wetaggregates is by reducing the amount of organic binding agents and hvdrophobIcitvt ig,re.,ates ‘Tisdall and Oido ‘2 Fig 4) \‘, discued eirlir l1ght ‘rsubcritical water repellency can contribute to aggregate stabilization (Coebel et aL,2005; Bottinelli et aL, 201. Crop residues are a source of transient, temporary andpersistent organic binding agents that are essential to soil aggregation. Transient orabile ‘ ii organ e r’attr raztic n brf rind soil partnJ n 1e.at s hik th

ot rm-kon r I,Jtr3nt eltOr r’s,t[, ceIud d n k aggr gtec

20041. Lkonstituents of soil org,anic mat..ei, particularly persistent fractions, react withoils valent ca000s, oxides, and aiuminos.it icates to form complex compounds andstabjlize aggregates (Tisdali and Codes, 19821.

The SOC concentration and. soil aggregates are mutually interrelated(Bossoyt et aL, 2.005). The SOCwnriched organic materials form and stabilize

,, ir L. OIL o so<soil prevent SOC fran rad doconwssojtion. tAeas’er aggregates store less oUt,,

than more stable aggregates. Macr<oaggregateprotected SOC is mostly labile andsoung with faster turnosor rate than ma rosoggregate protected SOC tPuget etal., 21105). Labile SOC fractions decrease more rapidly than stable or recalcitrantSOC Iracttons following residue removal (Karlen et al.. 1.994).

‘The degree at which the residuederived SOC associates with soilmineral pa.rticles and stabih.z.es aggregates depend.s on ‘the degree of residuede mposit r (K i ‘99” The a’ wia ot r LIdu i I ga’o mat’ n

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lmo3cts of Soil Organic Carbon on Soil Phsicai Behavior

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concentration. The Proctor maximunr bulk density decre.ased sig ni.fica ntlyas SOC con.centra.ticm mccvça -.vhe roar: Prsactor critical water content .ncr-ased.

CCX .:ancentraw .n increase .Proetor maximum bulk densit •f• criti.ca

water content were strongly correlate.d with cha.nes in SOC :oncentrationrosa rdies.s soil class w. 5O)P5

and climatic zones (Pie. 2--iCC and 2OSDi. Those resuits indcate that a decreasein SOC concentration can increase risks of soi.i compaction. Soil compactibility

is sensitive to management and may be more significantly affected by changesin SOC concentration than other soi physical. prenerties, The decrease in soilwater content at which the soil is most compacted due to the decrease in SOCconcentration is important to mana.ge soil compaction, The imp.I ica.ti.on is that

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also changes the strength of bonds a.nd electrica.i charges at t.he intramggregatet’ ‘o rt n rgn md ra’n to I

behavior of the soil matrix (boano., t990; Ball et ab,

The i.ncrease in maximum compactihilitv with decreased SOC concentrationan have in orta.nt implicatIons for managi.ng crap residues noel .011 compaction.

ft sugges.ts that residues s.houid he returned, to soil to male tam or increase SOCend to reduce. ‘f least in pains m- -t 1m risks to eve-naive compacm

to alleviate soil compaction has been on reducing axle loads, controllingamine and r’’nc” f ro1ifj0 aoi mpemefltn remedation ni-ensures .auchas ubsoil.ing. vertical till..age, and others. The ability of 5QC to i.nfluence t.he

o IS u° pt itol i ° c nve in h w hI 0 in C It 1 w 1 Ci a aexcessive soilcompaction. While crop residue mulch alone may not be highlye-ffbctive in reducing SOIl bulk density from an i.ncrease in applied stress (Gupta:.et al., 1987). SOC accumuIaton with continued residue addition may improve sodresilience a.nd rebounding capaci.ty in the long term. The role of SOC in alleviatingexcess-Cc oil compaction can he particularly relevant at lois than at high axleP ads I told quipmcnt torali bccmsc nT managenwnt is critic 0 to redave

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pore voLume, water retention. and soil structural para.meters, and changes in SOC

concentration had much stronger effects than changes in clay concentration,

Differences in SOC concentration may also affect porosity by altering soil

particle. densi.ty (Table 2—1). The few studies have available on this topic have

that particle density decreases with an increase in so concentration.

Across various cultivated soils in t.he iiy, Ball tt aL (2P00) reported that particle

density was negatively and significantly correlated. (r —0,38; P < 000i) with SOC

concentrat.ion. Sin. ilarly, across no’diIl, chisel pionc and. moldboard plow systems

in Ohic, BianccoCanqui et al. (2006b) found that partic.le density was• as sensitive

to changes i.n SOC c.oncentrati.on as bulk density. They reported that a decrease in

SOC concentration due to differences in residue managernen.t between notill and

plowed systems explaflied 38% (P < 0,001) of the variability in particle density in

the (P to lOwm soil depth. Similar to the effects on bulk density; the decrease in

particle donsfly with incirease in SOC coo.centration is attrihuted to the thintion

effect of soil organic particles. Changes in particle density can affect soil hydraulic

properties by altering soil porosity.

Ma,ny studies have shown t.hat residue managementilndrced changes in SOC

concentration alter water retentIon. On two silt barns in Iowa1 increased SOC

concentration by doubling the amount of corn stover for 10 yr in ncotill increased

plant available water at —0,5, —1.4, and —9.8 kPa (Karben et aL, 1994. On a silt loam in

Ohio, wheat straw addition to no’till plots for 7 yr increased both water retention

at >30 kPa suctions and SOC concentration in the (P to iOwm depth (I. uiker and

Lab, 1999). Correlations in Table 2—2 for three contrasting noflil soils show that

water retention and plant available water decreased linearly with a loss in SOC.

ccncentration due to corn stover removal (BiancmCanqui et al., 2G06a; Blances

Canqui et al., 2007). Decrease i.n SOC concentration reduces the soil’s ability to

a.bsorb and retain water because it reduce.s the specific surface area of the soil,

Orgaric particles have a . greater specific surface area and water adsorption

c.apacity than soil inorganic particles (Ra.wis et al., 2003). Hudson (1994) foun.d

that soils containing 4% organic matter retained plant available water twice more

th.an soils containing 1% organic matter. Obness and Archer (2005) found tha.t

change in *lant avai.iabie water ranged between 2.5 and 5% for each 1% chan.ge.

in SOC concentration for soifi with O.5% SOC and 40% cl.ay concentrations.

Recently, Kvaerno and Haugen (2011), while assessi.ng the performance of a

number of pedotransfer functions in predicting soil water characteristics ba..sed

on particIessze distribution, organic matter content, and bulk density acros.s 540

soil h.orizons on cultivated lands in Norway, found that pedotran.sfer functions

which included organic m.atten content as one of the input parameters were the

b.est predictors of soil water retention unuor low suctions.

rr acts of Soil Organic Cabon on Soil Physvai BehaOor

s.i.ze distribution to influence soil compaction. structural, and hydraulic properties.

The SOC bu.ffers risis of excessive sci.i compaction, incrc..a.ses soil aggreg.at.e ila

bi1it and streng.th. m:acroporositv, induces shyht water repellencu and

imriroves water retention.

The met hanisms by whc.h SOC influences oi physical propertIes are

numerous and compicx Organic particles stabIli?e soil aggregates by h riding

individual particles into stable ruts and. strengthening the irtenparticle cohesion•w ithin a.nd among aggregates.. Organic fih can also induce hydrophobicproperties. to soil, reducing aggregate slaking. Because crop residues h.ave elasticrepcr4wc inc icr d in m n p e1 wt cit pun hk

behavior, and reboundmg capact v to the whole soil. Organic particles also have

lower density than mineral particles, which dilutes the aivl bulk densit , reducingrisks of excessive compression and compaction of the soil. Prestsnce of a ne twork

of fine roots F ung.ai h .‘.phaeand other biologicai comp nents n agtofneralparticles a d increase friction forces among: soil particles. Organic particles can

iso impart uzbt oo c tr cal eb rge to the nOd simihir to la pu fiOes to react

and develop complex chemical bonds among soil particles to Further improve

soil physical moperties. These myriad benefits of SOCenriched materials can be

readily altered by management practices such as crop residue removal.

Crop residue removal adversely impacts soil physical properties by depletingSOC. but C input through highbiomass producing crop rotations (e.g., continuouscropping svsfems may maintain and improve soilphvsical characteristics. Residuerranagcment ritcg 0c e g no tub thai inceae SOC oneentration mprose

‘tr eturu mna ti nci }‘ lrauot rrp rt e’- r’ ma an’ in

in SOC concentration i.s s’ tron.gly correlated with maxi mu.m soil compactibi.lityand critical water content, indicating that cultivated soils with increared SOCconcentration are less susceptible to compaction and can be trafficked at greatersoil water content without the risks soil compaction conipa rub with soils low

concentration.

The numerous benefic al effects; of on ditterent soil chusical parametersut the need for maintaining .ptiirrtm levels of SOC through annual crop

ron idue .retur n and use of noRill farming to ma.intai.n or improve soil functions.Because excessive renrcvai i.:f crop residues for ofhfarm uses rea.di.ly reducesSOC conccmtra.tion., it can ac.lverselr affect soil is;hvsical behavior. Residue mulchimproves soil physical propertiru not only by increasing SOC conceneratinn

I ut aO h prot an the il —art icC tr rn the n e h FCt. ot raindr aed

cc dueing abrupt f.uctuation of soil temperature, freezing and tf.awing, andwetti.ng a.nd drying cycles. Overall, increasing SOC concentration throughproper crop residue management may n.ot only reduce net em.issi,ons of C to the

BiancoCanqui, H., and B, Lal. 2008b. Corn stover rem.oval impacts on microscaIe soil pf.ysic.alpnap€.rms. Geoderma 145:335—346., doi:10.10i6/jgeoderma.2008.03.0i6.

BlancmCanqui, H., B. Lal, B.C. lzaurralde, W.M. Post, and MJ. Shipitalo. 2006b. Organic carboninfluences on particle density and rheological properties for a silt loam soil, Soil Sci. Soc. Am.i. 70:1407—1414. doi:10..2136/sssaj200S.03S5.

BlancmCanqui, H., B. Lal, LB. Owens, W,M.. Post, and Mi. Shipitalo, 2007. Rapid changes in soil car’ban. and structural properties due to stover removal from notill corn plet Soil Tillage Bes.92:144—155. doi:10.1016/j.stilL200&02.002.

BlancoCanqui, H B. Lal, W.M. Post, B.C. lzaurraide, and LB. Owens. 2006a. Soil structuralparameters and organic carbon in notill corn with variable stover retention rates. Soil Sci.171:468—482. doi.:10.1097/01.s.s.0000209364.8S816.lb.

BlancoCanqui, H., LB. Stone, AJ. Schlegel, DJ. Lyon, M,F. Vigil, M. Mikha, and RW. Stahlrnan.2009 Notill i.nduced increase in organic carbon reduces maximum bulk density of soils. SoilSci. Soc. Am. 1. 73:1871—1879, doi:10.2136/ss’saj2008.0353..

BlancoCanqui, H., L.B. Stone, and P.W. Stahlman. 2010a. Soil response to longterm cropping systems on an Argiustoll in the c.entral Great Plains.. Soil Sci. Soc.. Am.i.. 74:602—611. doi:i0.2136/sssaj2009.0214.

Boivin, P., B. Schäffei, and W. Sturny. 2009. Quantifying the relationship between soil organiccarbon and soil physical properties using shrinkage modelling. Eur. I. Soil Sd. 60:265—275.do :10.1I11/J.13652389.200&01I07..

Bordovsky, D.G., M. Choudhary, and CJ. Gerard. 1999. Effect of tillage, cropping, and resdue management on soil properties in the Texas B.olling Plains. Soil Sd. 164:331—340.doi:10.1097/00010694499905000’OOOOS.

Bossuyt, H., 3. SIx, and P.R. Hendrix. 2005. Protection of soil carbon by microaggregates withinearthworm casts. Soil Biol. Biachem. 37:251—258. doi:10.1016/j..soilbio.2004.07.035.

Bottnel1i, N., V. Hallaire, S. MenasseriAubry, C. Le Guillou, and D. Cluzeau. 2010. Abundance andstability of belowground earthworm casts influenced by tillage intensity and depth. Soil Tubage Res. 106:263—267. doi:10.1016/j.stlll.2009.11.00S.

Chancy, K., and R.S. Swift. 1984. The influence of organic matter on aggregate stability in some British soils. 3. Sail Sci. 35:223—230. doi:10.1111/j.13652389.1984.tb0O278.x.

Chenu, C., Y. Le Bissonnais, and D. Arrouays. 2000. Organic matter influence an clay wettability andsail aggregate stability. Soil Sci. Soc. Am. 3. 64:1479—1486. doi:10.2136/sssaj2000.6441479x.

Davidson, i.M., F. Gray, and 0.1. Pinson. 1967. Changes in organic matter and bulk density withdepth under two cropping systems. Agron. 3. 59:375—378. doi:10.2134/agronjl967.00021962005900040025x.

Dc Jong, E., D.F. Acton, and H.B. Stonehouse. 1990. Estimating the Atterberg limits of southern Saskatchewan soils from texture and carbon contents, Can. 3. Soil Sd. 70:543—554. doi:iO.4141/cj.ss90057.

Do Jorge, L,W,, P. Moldrup, and O.H. Jacobsen. 2007. Soilwater content dependency of waterrepellency in soils: Effect of crop type, soil management, and physicabchemical parameters.Soil Sci. 172.. :S77—588. doi:10..1097/SS.0b013e318065c090.

Dexte A.B., G. Richard, 1.3. Arrouays, E.A. Czyz, C. Jolivet, and 0. Duva . 2008. Complexedorganic matter controls soil physical properties. Geoderma 144:620—627. doi:10.1016/j.geoderma.2008.01.022.

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