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111111.25 11111 1.4 111111.6 111111.25 111111.4 111111.6

MICROCOPY RESOLUTION TEST CHART MICROCOPY RESOLUTION TEST CHART NATIONAL BUREAU nr STANDARDS.1963-A NATIONAL BUREAU OF STANDARDS-1963A

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TECHNICAL BULLETIN No. 558 FEBRUARY 1937

SOIL AND WATER

CONSERVATION INVESTIGATIONS

At the Soil Conservation Experiment Station Missouri Valley Loess Region

Clarinda, Iowa

Progress Report 1931-35

By

G. W. MUSGRAVE Superintendent

alld

R.A.NORTON AMocIate Aerlculturai Eqlu..

SoU ComuYatlon SerYlco

UNITED STATES DEPARTMENT OF AGRICULTUKE, WASHINGTON, D. C. IN COOPERATION WIm mE IOWA AGRICULTURAL EXPERIMENT STATION

~................................................... ~_' ..... '... .. ..,.. ,. '-'" "" ' .. 'AI"'AI' f:~ " ................................................................................ ......, ..A" , . ' t .... .. .. .........................................................................................................

Forl.le by the.SuperillteDden~of Documents, Wa.hington, D.C. - - - - - - - - - - Price 2:0

Technical Bulletin No. 55g February 1937

tJNITED S1:.NfES DEPARTMENT OF AGRIC1.JLTURE

WASHINGTON, D. C.

SOIL AND WATER CONSERVATION INVESTIGATIONS AT THE SOIL CONSERVATION EXPERIMENT STATION,

MISSOURI VALLEY LOESS REGION, CLARINDA, IOWA

By O. 'V. Musr,nAVtJ, sl~lJCriule1Lrlellt, und R. A. NORTON, nssodnlc II.gr{r,u[tnral engineer, Soil ConserlJation SCTllice 1

The United StatE.s Department of Agriculture, Soil Conservation Service, in Cooperation \Vith the Iowa Agricultural Experiment Station

~~ h~ Introductlon. ~ .,. ... . ~. . ., Hesulis. ....... .... . 21 Distribution of loessini soils in tho i\l issouri Controliliots, experilllent L............. 21

Vnlley lind IIssociated 'nens......... ...... :1 Soilmoisturo detorminaU(lns, control I.ocssinl soils in lawn.................. .. 3 plots expedrnent 2 at Locsslal soils in 1\ebrnska................ ~ Appiirntion of orgnnic 11utter, experi LoessinI soil~ in MissourL... '"",. " ment:!............................... . .l! LoessiaI soils in Knnsas... ..... Ii EfTect of length of slope unrl dlrectioll of

Type of erosion.............................. 6 row, experiment 4............... H . 50... Some fllctors afTecting erMlo~................. U Elements of the control problem .... 53 Dcscription of the proJect.. ................ 8 Canopy interception .. ,;4

,,6H:;,~OrU;ti(;ri ;,nh(iinr,il:::::::~::::::::: ~ IInfi~::r..~i~~~\,i(ic;i;eiintl;crili~iiiffniiitriitici,;:: 1i6 Principnl ohJec!h'es ..........._... .. .... 10 ElTect o.f trenlment C!n relnti\'o illllitmtion

PreciIlltntion.... __ _.. _..... .......:0 ns derJvClI fromlysunelers ........... , .1S Monthly rainfllll u\ernges................ 10 Indirect evidence on tile roto of inOlt.ra Expected frequcnt'y of intense rninfail in ! tion................. _................ .

lawn............ . ""'" ., 13 Surrace impounding ................ _......... Other climatological rccIlr(\s _ 1:1 Methods..........

Purpose nnd plan or experin'cnts. I' Degree of land slope and surface Impound Control plots, experiment I.. ... 17 age.................................... . 59 t.ysimeters, eX!lcrlrllcnt l-D.... _ IS Helntion o!soilinfiltrnUon cllpacity to the SoiluwIsture studies, experiment 2.. .... 19 practical vlllue of surfnce!tnpounding ElTect of organic lIlatter upon runolT and treatments............................. 59

erosion ami upon the renewnl of fertility ','npor losses .... _... no in eroded soils, experiment 3 .. _.... 19 Surfneo runolT. ..................""" . fi\

Length of slope and direction of row, ex Densityofrun-otT. ...................... . 02 ]>criment 4............................. 20 Strip cropping .............................. . 6,)

Infiltration studies, (Ixperiment 5......... 20 SoU moisturconlerracod lind unterrnced nreas. 66

, 'rhe chnmher of commerce of Clnrlnda nnd Shenandoah, lawn, and lhe Page COllnty Farm Dureau also cooperated in furnishing information. 'I'he work reported herein wus /lrst organized in the Bureau of Chemi[try und Soils and the 11urenu of "\griculturnl Ellt;ineoring, and consolitilltml Al)r. 1, 1935, in the Soil Con~en'!ltioll Senice. Tho Oliginal plan of work wall largely p(oparcti by If. 11. Dennell, who was III immedi"te chargo of the Soil Ero~ion Investigations for tbe Burcnu of Chemistry and Soils. and C. Eo Ramser, of tho Burellu of Agriculturnl Engineering. A. O. ~rcCIIIl, Chicf of tlll\ Division o[ SolllnvcsU gations, n. V. Allison, lately in chllrge Of Soil Erosion lm'csliglltions of the Burellu of Chemistry and Solis,,ind L. A. Jones of the Bureau or Agricnlturnl Engineering' (iuided many of the brond plans of the work. ~lany individunlsha\'e contributed to \'arious pha'5os of the plnns and nssisted in the de\'elopment of the program, jJarticularly P. J-~. Brown, J. D. DIl\'idson, lind 0.11. ~rcDonald. ollowlI State College,und 11-1. ~', Miller, of the University of l\llssouri. Acknowleclgmcnt also is made of tho very conscientious and carefnl work of a number of assistant.s on the station stalT, particularly J,. S. Cutter, n, H. Free, Annn Cramer. Dale '''inger, Leo "'heeler, und muny others wb

2 1'ECHNICAL BULLE'l'lN 558, U, S, DEP'I', OF AGRlCUL'rUm~

CONTf;N'fS-C'ontinucd

J?llgO f Puge Soil mofsttlcc on terruced Ulle! unt.erruel'(l R~pcriuwn(s nurl rest-Ils of run.ofT nnd erosion

nrons.-Continued, froUllcrmect! nrclls-Continued, ~Iois(urudistrlblltion ncross two 101"'1 (('r Shor~ (crnlccs with dllfercnL Jlrudus nud

tM'es. "" - .. - ............ __ ..... 611 sullie \'crUmlspnelnI:R,Cxperuncnl.lOr.._ 10i ConstrueLlon oftcrrnecs,lIIothods, nnd eosIS... 70 Oraded tcrrnecs of (Iilfcrcnt Icn~1 hs und .Erosion control ill gullies nnd ton nccoutlet SUIIIO 1"'rLlenl ~Jlndngs, CXP('CiIllClll106. _ 1JO

ditches, nnd chot'king erosi()u lit terrum J_el'ct tcrlnCUS with opcn cnds IIl1,1 dif. I' 7U fercnt Icn!(ths. CX\Jecilllont 107.0. " __ ' 1 /oJ

Soi~I~I~~;~~;~n~-J~;~;(til;;~l~I;~~::' ::::::::::: 811 L1~~ntC:I~;;gf~g~~i~X~J~Ji~:~I~~IJ~~~.'~I.I~I__(~~(: llG OperllliOll of fflrm Jl111ciJim.'ry OJ) icrm(" ..d s- Sllort 101'01 (l'rmel'S wilh ciosl'd onlis. ex JIG

nrcn::;~~_._ .. _,. .................... _....... ~_~~~~~ .... _, 4_~~~~ ~ ( peritIH,'llt lOH ~,_ ........... _ ~ .. _....._.. _~ .. .. Experimenls nnd resulls ofTllnolf nnd erosion ~[unl1rill!l fcrmeed /1111(1, l'.

3 SOIL AND WA'l'ER CONSERVA'l'ION INVESl'IGA'l'IONS

likelihood of change in nny conclusions which mny be drawn following a longer period of e)q)el'imentn,tion.

DIS'l'RIBUTION OF LOESSIAL SOILS IN 'rHE MISSOURI V ALLEY AND ASSOCIATED AREAS

1']le soils of the :Missouri Valley loessin.ll'egioll comprise some of the most fel'tile soils of the United Stutes; theu: lo('utioll, shown in figure 1, hordering the Missouri RiYer Valley nnd tho Stntrs of j\{is

VlGI'Hf1 1.~~I*lrihlllioll or .\!issuuri Ynller loess Ulld IlSSoclHterl jnl'ssl,,1 rorrnn1ioll~.

f;ouri, :Kunsns, lown" N cbmskn" l\{illucsotn" nncl SOLI tIt Dn.kotn, coi.ncidrs with t.he more intensive p01't.ion of the COl'll BrIt.

LOESSIAL SOILS IN IOWA

'rhe loessin 1 soils of lowu nre genel'n1ly dh'ided into thl'ee importunt groups, the :Missouri loess, the :Mississippi 10rss, nnd the soutilern Iown, ]orss. The :Missouri loess mny be furthrl' suhdivided into the ligh ter-colored, more Tolling bluff lands, n neT the dUl'ker-('olored pl'niriu lands. 1'heligltt-colorecL bluff Innds nrc extremely lH)l'lIlrflble, very deep, and rendily nbsor'b wnter. Ho\\'cver, bectluse of the stecp topogmphy unci certain physicnl properties such ns a, high degr'ce of dispersion, they !lTC highly erodible nnd especially susceptible to erosion when cxposed to the clements through tillage. Origin:llI)T these soils 'were timbered and in mnny purts of the urc!I. IlTe st.ill COVered with n, forest growth. Much of the cleared soil should bc

4 'l'ECHNICAL BULLETIN 558, U. S. DEP'l'. OF AGRICULTURE

returned to forest; it is the only practicable means of handling such lands, which often exceed 25-percent slope.

The dal'kcolored prairie soils of the Missouri Valley' loess nre represented principally by the Marshall series. These salls are deeper on the western margin where they approach the bluffs and become increasingly more shnllow to the eastward as they fino11y fude out by merging with the drift of the central portion of the State. In the eastern pnrt of the Stl1te the MississippI loess is represented primarily by the Tama series. This soil does not differ grently from the Marshall series except that it is almost devoid of lime wherens the Marshall generally hns an appreciable lime content. The Tama series mny in certain mstnnces be somewhat heavier in texture than the Mnrshall and somewhat less absorptive of wn,ter. In general, however, the erosion problems on the Mississippi loess are not outstandingly different from those on the Missouri loess.

The southern part of the Stn,te, generally described as southern Iowa loess, contains at the present time perhnps 50 percent of its aren as exposed drift. This area with its heavier subsoil and very low rate of wntt'r intake is characterized by excessive erosion and widespread gullying. The erosion problems of this area are being studied morc fully at the Soil Conservation Experiment Station neur Bethany, Mo.

LOESSIAL SOILS IN NEBRASKA

The loessial soils in N ebraslm are the soil covel' of loess hills and loess plains. The soils of the loess-hill area adjacent to the Missouri River are not gren,tly different in chemical and physical properties from those on the eastern side of the same river in Iowa. However, the loessiul soils of Nebraska, particularly in the western part, frequently are characterized by a zone of lime accretion, and in this respect difrer from the soils of southern Iowa, which do not ordinarily show excess carbonates.

Stewart and Gross (12, p. 14) 2 state: The soil of the western portion of the loess hill area and that bordering the

sand-hills contains a higher per cent of sand than the soil of the eastern part. In the west, the soil is also lighter in color in both the surface and subsoil. That portion of the locss liills south of the Republican River is steep and rolling. Canyon lunds bordered by level irregular tablelands make up milch of the area of southwest Nebraska and this region might be classified as loess plains and canyon lands.

The Locss Plains stretching in triangular shape from Seward County west into Gospcr County is an extcnsive level area. The soil forming material of this area is thought to be of the same origin as that of the loess hills. The soil is very fertile. Due to the level topography, erosion is not usually a problem and large farm machinery can be used to advantage. In parts of the loess plains a "clay pan" hus been developcd by the percolation of water carrying small soil particles into the subsoil where thcy Imve lodged making a tough "clayey" layer which prevents rapid pcnetration of watcr into the subsoil. Small grains, because of the fact that they ripen earlier, do relatively better than corn on such "clay pan" soils.

The western margin of the loess area borders upon the sand hills and in this respect is distinctly different from the eastern margin within the State of Iown, as well as southeastern Nebraska. In the latter arens the loessial soils border on glacial drift of heavy texture.

The erosion problem along the mar~ins of the region where it borders upon or overlies these heavy SOlI formations is quite difl'erent from that wher'e it borders upon or overlies the sandy material in

'Italic numbers in parentheses refer to Literature Cited, p. 134.

5

t

SOIL AND WATER CONSERVATION INVES1'IGATIONS

western Nebraska. With the permeable subsoil conditions on the westerly margin there is ready downward movemen t of water, nnd the erosion problem along the margins does not din'er nppmeiably from that within the loessial area propel'. On the eastern boundmies, however, because of the heavy subsoil, the erosion problem becomes increasingly difficult from the helLrt of the loessial area to the margins and finally into the area of glacial drift.

LOESSIAL SOILS IN MISSOURI

The distribution of the brown loess (bluff lands) and the dark loess (prairie lands) in Missouri is pOTtrayed by Kl'usekopf (2). Within the confines of Missouri the loess forms an almost unbToken belt of upland soils along the Missouri and Mississippi RiYers. The darkcolored soils, however, are located principally in the belt along the Missouri River extending from the northwestern cornel' of the State to Boone County in the central portion of the State. Krusekopf estimates the total area of the brown loess in Missouri at approximately 1,500,000 ncres, n~d states that it occurs in 41 of the 114 counties of the State. He states further (2, p. 7): ''It is probable that no other State in the Union contains so lal'ge an aretl or has them so widely distributed. "

The area of the dark soils can be estinlatec1 from the fact that they are of appreciable extent in 18 counties in the northwestern portion of the State.

The bl'own loess in its steeper slopes and general rough topography is particularly susceptible to el'Osion. To some extent these adverse conditions ha'le been mitignted by the high permeu.bility of this soil. However, when the surface is exposed through cultivation, ns is rather common in connection with the extension of the corn-grov,,-ing region into the bluff area, large qunutities of soil are lost during intensive rains. The dark-colored soils, of which the MaTShall silt loam is the principal type, present approxinlately the same erosion problems as those found in the same belt to the northward within t.he confines of Iowa. For the most part this soil grades off to the eastwm.d into the heavy types of the glacial drift, and in these mal'ginfJ the infiltration of water is greatly l'educed by renson of the heavier subsoil. Consequently gullies are more pronounced and sheet erosionlikmvise is more active on this eastwu.rd margin.

The loessial soils in the eastern paTt of the State are represented largely by the :Memphic:; series and in some sml'11er nreas by the Clinton series. The Memphis in geneml is a lighter-colored soil than the Marshall, but having been developed under higher l'l1infall conditions is more highly weathered and is characterized by a subsoil of a bt'own to yell,:nv-brown, fairly heavy silty clay. It is not compact but is less granular than the corresponding horizon in the Knox or in the Marshall series. The Memphis soils which extend farther south into Mississippi are particularly erodible, large gullies being formed which aTe characterized as the "pinnacle" type by reason of the prominent pinnacles of subsoil protruding from the margins and bottoms of deep cnnyonlike dminageways.

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6 'l'ECHNICAL BULLE'I'IN 558, D. S. DEP'l'. OF AGRICUL'!'URE

As a whole, therefore, the erosion problem on these types is a serious one. This is pnrticuln,]'ly tl'UC in the ligh t of Ifrusekopfls statement (2, p. 54):

The loess soils reprcsent the most. vl1llwble single soil resource of Missouli. They cover approximately one-eighth the l1l'ea of t'lC State, but ill their relation to the agriculture of the State they occupy first place.

LOESSIAL SOIlA'3 IN KANSAS

The distribu tion of the vn,l'ious soil groups in KftllSnS including loess is shown by Tlu'ockmorton (1:3). The soils of the blufl's adjaeent to the Missouri River Valley u.rn described fiS typically deep und have un open subsoil whieh permit~\ deep penetration or water und roots. The fertility is high except ill those arellS where erosion is H('tivl'. 'fhe topogrn,phy varies front rolling to distinC'tiy hilly. These soils nre extremely subjeet to erosioIi and in some urens flS llIu('h ns 18 inC'hes of the soil hns been removed by the 11('tion of wnt!'r sinee the land was placed under cultivn,tion.

The northern wind deposits (nort.lnvestel'll Kansas) arc gl'Ouped and described by Throckmorton scpnTQ,tely (13, pp. 97-99):

Except in the vicinity of :::tr'eams these soiis are level to rolling * * * They are relatively young, do not have a clay-pall dm'(}loplllent, and have subsoils which are sufficiently open to l1 I:\"n'at depth.. These soils are high ill plautfood ll1ateriuls * * *. There are llIally areas within this region adjacent to the streams where the wind-laid soils have been erori('d away * * *. 'l'hese wind-clepositpd soils :tre subject to erosioll by buth willd and water Ilnd, thercfore, must be handled with cOllsiderable care. There al'e many fairly Jal'ge al'cas of these soils in the llorth-centml palt of the State that have been severely injured by wuter erosion.

TYPE OF EROSION

The region is characterized by ex('essive sheet erosion. To tL minor extent gully erosion prcvflils but the gullies, for the most part, occur infrequently. In mnny instnnces, however, they mc of cavernlikc proportions and show a rate of gmwth which is almost unbelievable. Specific CflS(,S are rceorded showing udvnnces of one-fourth mile and more in length andln.tf'rnl growth exceeding 100 fept in a single yenr. The greater dfl.J11nge to 1'1I1'm vlllues and the agriculturnl region flS a whole is thnt causecl by sheet erosion.

In genernl, erosion within the 11issouri Valley loess region hns progressed to such an extent that more than 50 percent of the original covering of surface soil, known llS the A horizon, hns been removed. In many instan('es the entire loessinl covering has been removed by washing, ancl there is then left an exposure of KftJ1Snn drift, the soil of which is elnssified in the Shelby series. The removal of such vast quantities of soil, at a rate \'thich covers the period of the past 75 yen,!'s, indicates the extreme nccessity of early und vigorous action for control.

SOME FACTORS AFFECTING EROSION

11any factors, of ('ourse, affect the degree and extent of erosion which occurs in any rcgion. Among the more olltstnndingof these in the region under discussion are:

The frequency of rather steep slopes, ILnd the fnrming of slopes .r!Lnging from 6 to 20 percent.

The relatively Jarge proportion of corn in the cropping system. The I-year tenantry system.

SOIL AND WNfER CONSERVNl'ION INVESTIGATIONS 7

The large proportion of mortgaged land. Large capital inve!Stments, rt'quiring intensive tillage in order to COVer the

ctlrrying charges. Large size of [arms resulting in C0I111110n usc of large-scale farm machinery. Intensity ane! amount of precipitation.

Certuin of the ceonomi(~ fudors nre indicnted in table 1, which furnishes 11 complll'ison of those Iowl1 counties which hllve 50 percen tor morc of their IlJ'CIl, lying within the 10essilllrcgioll with the remuining countics of the Stntc.

TABLE I.-Comp(/rison oj JOl'1II8 in the /orssial-l'egion countirs wilh those 'in othl'l' cOl/nti('s in [OIl'/!,

- ---------------~---,---.-~ -~---------:----I '

1,lIl'SS!!11 I Ot her " Item Locsslnl OtherHem ,~:~_ counties 1'___________CO_lI_III_le_s _co_lI_lIt_ifJ_S 1

\'01111) 01 Innd ntld huil"ln~s ITny per 1,Irm .... _... , . neros .. 13.0 17.5" per Inrm, ..... _ doIlnrs. ~:J,(;07 )S,Ol-l Pnslure per rllr11l~~~,v~ .. do" _. aO.7 40.2 \"nll1o 01 lnlld nnd hlliltlln~s CnUle per Inrm. _.. lIlImber" ~>(J, 1 19. 0

per ncre...... , ..doIlnrs 1-11 110 R\\'ino per IlIrlll ........110 .... 59.0 43,4 \'nluoollnnd pcr Illrll1 t1o .. JSt 512 la,RI\I 'I'otullund lI1ortgllgclrcu \'ulucollnlld pernrrc .do III 09 I'erl'cnt 11.5 16.8 1I1Qrtgllgo debt per Inrll1 (lull Fnrms III ItlII owners lip

owners)...... "... " dollars i,(HI 'I,OZl perccnt a5 40 f'lzcol!lIrll1 (nil Innd in IlIrmSI Proportion 01 lenllnls to lull

nt'r('~ Hii.5 15';, ~ owners........ _...."_........ rntio~. 1,5:1 1.1:1 ('orn per Inrll1........ _.do Oi. I 4i.2

I'

'Csing the l()('ssinl-region (,olin ties of Iown, ns an index of conditions within the :Missollri Valley 10essinlregioIl, it is secn thnt, in geneml, the farms in the countil's within the loessiul n1'en, n,vcmge somcwhnt larger than in those coun tics Oll tside of the aren. The land nnd buildings also hnve a gl't'atel' vnhw, both to the form and to the :1cre, und the value of land exe1ucling buildings is likewise higher, both pCI' fnrm und per Herr.

li'lIl'thcl'l1lore the 1935 ('I'Op ('ensus for the Stnte shows a more rapid illcr'ense in 1':11'111 tennwy in l'rcrnt yenl'S thnn formcrly. The 1111111bel' of fnrllls opl'l'nted by tpllHnts in 1935 wus shown to be 34 pcrcent grCflter thnn a qunrtrr of n. eputllry cfll'liel' unci 8 perl'.rnt grctlter than in 1930. The :wernge incrcase in lnnd opernted by tennnts since 1910 W(IS even greater thfl!l the increa.se in ll~'111bcr of tenunt-opern.ted farms, it 36-prl'C'ent gUlIl fOI' til(' 25 yenl's hemg recorded.

These factors unqucstionably affect farming prn.ctices to fin importl1nt extent find, consequently, thJ'ough methods of opemtion, have n.n importn.nt effect upon the degree of erosion. The low percentnge of hay n.nd pasture land n,nd the lnt'gc capitnl hlYestment "ith its accompanying mortgltgc d~ht (pr(,Vl~.le.llt in the loessin.l region) n.re pnrticulltrly potent factors III d('tennuung types of mnnn.gement. A farmer with a large cnpitnl irn'cstment and n. helwy mortgage is forced to put n. rather Inl'ge proportion of: the fllnn area 'ill to coj'n which, of course, is highly conduciyc to crosion. Also, the large ratio of tenn.nts to full owncrs, and tenn,nts Wl10 ol)('rate under the comlllon l-yen;r lease system, llt1.tumlly brings n.llout flo farming practice thnt will provide large Itllllun.l cash returns without rcgn,rd to the future status of the farm or fertility of the soil. It mILY 'be quite possible that these cconomic factors have us great, 01' grcntf'.I', nil effect lIpon the 1'llte of erosion than have stich physicl1l factors ns min intcnsity, soil cilarn.ctcristics, or In.nd slopes. Certainly it is not unrensonn.ble to nssume, in the light of yr.esent )mo~dedgc, that by adapting 11, good farming system to the eA'lstmg SOlI, clnnatc, and land slopcs, erosion mn.y be largely controllcd.

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8 1'ECHNICAL BUIJLE'l'IN J)!i8, U. S. DEPT. 01

-V===---t---~--* o"'0

CONTOUR INTEFiW..., 2 FEET

UPLAND !\OILS TtIlUct: SOILS Wr.l''''HJ.LI-o !SILT LOAM .. t-.. S'"!NCWSlV& to JVO~ ~., LOAM 5"0 MAR.5NAU. 51LT LO.fM -"-~INCLUSWC 40 JUg~o., !IoILT 1.O"... HtAVV wason.,"'45(. 54XC,1 ~\J.. $I\..T LCAM-tCf,.UKLVSlVL &0 &'i.UltIl S\LTY tu.... \'OA.M 4S0 MAR!YiAL.1..,5ILT LOAM-IB- PW, '0 LINTON'A 5ILT LQo\J.A 4'0 MAR:5HA1.L 51LT LOAM TAI.U$ SLOPt: .. BeNCH IJtt .6oCJ MAR!HJJJ. ~ILTY CLAY LOAM 440 ,HtLBY LOAM 13c:J ~~tL&'f ~ILT LoAM 140 !>HtL,&Y ,5IL,. LOAM Deep PHA5C Ctxtln I."'-Z&") JSO SHeLDY 'It.TY ClAY LOAM-YctLOW SUQrACC 5OfL5 31 c:J ~CLey ~LTY cu.Y LOAM Dttp PK&.~(tCf" 18"'U' 31AC $HtUY "LT LD4M"CO\lu.,m.ev tOAD ~ UC 'HtLbY OtAV"tU.Y 'ILTY cu.v L.QU,t f I aI IG6.N5AN PIln 5ILTY GLAY LOA..... ~.:5UIt'ACt. S I CJ

CONV1:NTIONAL SIGNS OUlt4.a.Gt.WAVS -- CON'T~~ l:1~t.S -~-:lOlL &OUJJOA21~ -_..... $TAnoN5 roe. TaI.u.cwUTION 4 fA.

]~~I~~~~~~~~~~~~~~~~~~~~~~~I\

FmURII: 2.-Map of the fBl'll1 of Boll Conservation Experiment Station, Missollrl Valley loellS region; BolIsBnd toJlOll'B'Phy. 112821 _37 (Face p. 8)

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9 SOIL AND W Nl'ER CONSERVNrION INVES'l'IGA'l'IONS

and stream bed of Walnut Oreek nre fairly well stabilized by grasses and trees, and no attempt has been made to reclaim it. A continuation of this stability would be nssured by fencing the gully to prevent stock from tl't11~pllllg the banks and caving them. The other large gully has been named Plum Creek. It dl'l1ins a totul of 125 acres, of which about 89 acres are situated within the station farm. Since the bed of this int,ermittent stream wns not stubili:wd, it plan for the control nnd reclamntion of this gully has been instituted. It will be described Intel' in this report.

Evidences of seriolls sheet erosion hnve been observed from time to time on the station fnrIU since its estlLblishment. There is no reason to believe this proeess has not been going on eyer since the fields were first cultivnbed. A particull.l'ly noteworthy exnmple of sheet erosion occurred during the autumn of 1931, just followinp.; prepamtion of the seedbed fi,ncl plnnting of n rye COVcl' crop. At tlllLt time unprotected

FwUlu: a.-Acrlnl view of tho furm o( Soli Cons~rvnUon BxpcrirllonL StnUon, 1\lIssourl Vnll~y loess region June 2(1, 1031.

u.J'eas were cu~ with minin.tul'e gullies about 1 to 2 inches deep which were distributed all over their sl1l'faces. This sheet erosion occurred during a rnin of approximn,tely 1 inoh, which wns not pnrticuln.rly intense. The detailed erosion nnci soil survey which wns mnde during 1931 shows thnt grent amounts of sheet erosion have occurred over practically nIl the steeper slopes of the fnI'm. In fnct, bordering the gully which is designnted us Plum Oreek, uU the loessittl mnterial (Marshall series) 11n,s been wnshed awny, nncl the underlying glacinl soil (Shelby series) is exposed. On the east side of field A, the tendency for the soil to continue washing down tIle slope is checked by the public road. At the foot of such slopes there nre deposits of loessialmateril1las much as 3 feet deep. A topographic and soil map showing the condition of the farm at the time of the establishment of the experiment station is shown in figure 2. An aerial photogl'l1ph (fig. 3) shows the genern.l fentures of the farm as they appeared on June 20, 1934.

10 'l'ECHNICAL DULLE'l'lN 558, U. S. DEP'!,. Ol~ AGRlCU1/l'Um~

)'IUNCIJ'AL OlljIWTIVt:S

'1'110 primary purpose of tho pl'ojoet is It quuntitntiyo study of tho soil and water losses nnd their ('Husal fnctol's. It is desired to Ielll'Jl the methods that mn,y be l1S('d 1'01' l'etlll'cling the losses of soil and wn hI!" find particulnrly tho pl'U.('timhle methods of rdtmling the ll1oyemel1 t of soil-carrying Witter. It is nlso desired to l(ll1l'n what methods mllY be used to renew the fertility of el'oded lrmds so that they lllllY li('retumed to fi profitable type of ngricultl1l'e. .

lncidentnl to these mnjor pu l'pU~('f! fire the dn,tfi being acquired J'tlln.ting to the efl'('cts of (']'osion und water 10s8(,s upon crop yields; the type of ngriculturc most suited to the problem Helt, Jmviilg fit the sallH'

time fi ndtignting cJl'eet upon soil nnd water losses; tho cost of contl'ol lllensuJ'('s for returding soil nnd

351-1-11-1 wntl'I.' loss('s illrelntion to the ll10])etn,ry cinll1llgc cnusedby suehlosses, nnd tho genel'lll pmcticability of

;10 vnrious specific conservation niens~

Ul'l'S fOl' wide applicl1tion upon theII) w ~ 25 soils of tho MIssouri Vnlley loess Z problem nl'('n.

o z

20 PRECIPITATION ~ I- Detniled prccipitntion rccords ~ 15 Ilrc regularly determined for 11 uI U difl'erent locations on the farm. a.

101-1--11-,

a: Tn ncldition to 'Yeather Burellu type. rnin gages nt each of these ]oclltlOns thcre arc also three

5 recording min gnges of the }i'm'gusson type. In I1ddition to these gages two gages 3 feet in dinmch'r

o AN r Iwe 10cI1ted ndjnC'cnt to the lysimeter instnlhttion with about til('

FlC1ung 4.-AcculI1ulntcrl prccipitntlon Soil sallle exposure above ground.Conscn'ntion l~xfleriment Stntioll, lIdssouri Vnlley loess region, l'ugo ('OUIlt.y, lawn, for There nlso is a "Yenthcr Burenu I!l:U. Lino hounding shnded IIrell shows nccullIulllted deptn of pret'illitlltiou ill inches. type gnge which is located with nn Smooth (!lln'o shol\'s IlOrIJill exposure similar to that of thc

lvsimetcrs. It nppcrtrs importnnt to mnke a systl'lllntie study of the exposures

of min gages, Jn the records which cxist n t this stlLtion nt the present time, those gages whiC'h tlm eXl}QsNl hu t fi 1'('w inches nbove the ground surface very consistently record fi clltdlll1ent considerably greater than that of nearby gnges linving the standlHd abovc-gl'ound exposure.

The dctniled rninfaH rccol'Cls for the various storlllS nrc presentcd nill connection wit the run-off.

MONTHLY ItAlNFALI, '\'YEIt,\GES

It is importnn t to make gcncrnl ('o111pn risons of thc l'uinfnll for the, i) years of opcration of' tlie stlttion. A C'olllplIl'ison of the aetunl 1'1l1nfnll with the normnll'lIinfuIl is shown in figures 4-8, nnd table 2.

11 SOIL AND WA'I'ER CONSERYA'.I'ION INVES'l'IGATIONS

35~+-~-+~--j--4--+-+~I--+-~~

FWt:IlE 5.-AcclIInulllted Ilrecipil,lItion, Soil ConservntiOIl Experiment StutiOJl, l\li~sollri Valley loess T(!gion, l~age COUllly-, Town, for 1932. Line bOllndiJl!( shlldcd llI'ell shows lie, CUlllulllted depth of preripitlltion in inches. Smooth eun'r shows norlllnl.

FIGOIlE 7.-Accumulnted preCipil,lltlon, Soil ConsermLion Experiment Stntion, M issollri VaUey loess region, Page County, 10'1'11, for 1934. Lino bounding shaded nrell shows aeculIlulated depth of precipitution in inches. Smooth curve shows normnl.

4 0

~

30

V- I---'

12 'I'ECHNICAL BULLE'I'IN 558, U. S. DEPT. OF AGRICULTURE

In these figures the normall'ninfllll is calculated from a series of nearby 'Weather Burcnu stations, the records of which ure weighted in inverse proportion to their distlUwes from the Soil Conservlltion Experiment St.ation. This weighted Iwernge is then corrected in aecordance with the compn.rative records of these stations and the farm for the first 4 yellrs of operation. This pro('edure is followed bernuse the nearby stations, loeated in rivl'l' valleys without exception, show higher rainfall than that, of the Clarinda stlLtion farm which is located. upon a watershed divide.

TABLg 2.-Comll(ln:,~()n oj {/('11l1l11(I.illfaIl1I'ith the 1tol'llwl rainJall at the Soil COILservlltion R.rJlcri'lllcllt ,')tl/Non in. tile Jlfi'.~,~()/lri 'Valle!] b('.~s '/'('(1 io It , l.'J.'1,2..,J5

:\!nnlh 10:1" (,I"rindll!A \:er:;~o f Norlll I JH:M2-.35 It (l\"crage '1 .-- --- ------

1url".., 111c/l"., JlIrlll.~ 1I1chr., illchr., Illches 1I1cilr. January" I. 1;1 0.:12 O.fil O. iiI o . n 0..18 n. til Fehruary.. _. .;2 .OS ~ ~n ,;1 . '''1 \9 ). O!I MarciL. ..1-1 :I. lUI .11 ,21) .117 .78 I.m April.. .72 iii 1.11 2.fi.' 2.79 Mny. ~::f~ a: i:1 2.MI '.liS 1.22 -I.M 1.-16 June.. ft. ~n -I. II 2, :li 7.00 1.70 S.42 fi.OO July.... 2.:12 2.27 1.2a 1.11 1.81 2.95 Ur, Au~ust .. _. K 10 r..H!I 2.1-1 211 .\. 7f> :l. 8., :1. 18 i'iepiellll1eL I. !IS 1.21 1.82 ii. )1 4.01 :1.70 a.82 October.... . un .87 2.81 :1.0:1 I.OR 2.61 2.67 No\cmber ..... .. 1.1-1 .12 a.5.t 2.f.O 1.110 1.31 1.-12])eecmbcr.____ . l I.ns I.OS .Ia _~= __,_Ii! ~I~

I---;;I~/ ")0 i---:-'-'1 .'I~Annuul 21.22I - . - -. ( _ ;l=~~_2~ ~Ii_ !!I/.70 I 32.43 .-~'.,.--- '-

I Calculnted frum adjllccllt Wcat.her Hurellu slnl.ions alld eorrueted for stailol1 results, 'Hyenr nverago 1.'. $. \\'onlher Hurollu; JO miles from stlliloll.

An examination of these ehnrts (figs. 4-8) shows that in 1931 the rainfall nt the stl1tion waS helow normal during the summer period, but the ye!u' closed with nn acculllulation above normal. In 1932 the actual rainfall nPPl'oximnted rn.thel' closely the curve of the nOf:mal acculllulated precipitation. In 1933 the chart shows a significant decrense, a negative depn.rture beginning with the month of May and continuing to the close of the yenI'. In 1934, the drought year, very mnrked negn.tive departures are found. The year 1935, however, again shows a minfall-accumulntion curve which lies somewhnt above the normal curve throllghout the yenr except for the period from t.he middle of Mn.rch to the middle of May. The year ended with a positive departure of appro;..,i.mately 2}~ inches.

In order to indicate the relative intensity of minfv.lt for the various rears, table 3 and fie-ure 9 have been prep!Lled. They show the total Inches of precipitatlOn above vU:l'ious designated intensity classes. This figure shows the lowest average intensities to have occurred in 1934, nlthough the totiLl nmount of rainfall oecurring in the highest intensity cln.ss (2 inches per hour) wu.s about the same for the years 1932, f034, and 1935. 'l'he highest average intensities n.ppn.rently occurred during 19:32, nlthough no striking. differences in average intensity 1111.\'e :.LppeiLrec1 in the records.

http:minfv.lthttp:H:M2-.35

SOIL AND WATER CONSERVA'l'ION INVES'l'IGA'l'IONS 13

Z8r-----------,------------.----------~----------~

~ Z6' \:> 1932 1.93.3 /934:t 24~ q: 22

~ ~2p

~ /8 ~ ~ /6' ~ li1/413 ~ /2 ~ ~ /0 ~

~ S

For other climntologicnl dntn the reader is referred to the records of the \Yenther Bureau and pltrticularly of the Iowa section. In nddition to the precipitation records there are thus available daily

http:4.5020.21

14 TECHNICAL J3ULLEnN 5,j8, U. S. DEPT. 01

SOIL AND WA'I'EH. GONSEH.YA'rIO~ INYESTIGATIONS 1:')

additiona,l quantities cnter into the ground, n,nd still othcl' frn.ctioIls are lost as surface run-ofl', Insofn,r as pl'llcticnhle it is dcsircd to determine the amount of wntel' vapor lost as cvnporfl,tion from the soil nnd as tm,nspimtion from growing plants, In nddition to the qunntitfltiYe detcl'lllinittion of these V:1riOllS nmounts of watpl' ns they may he lost in one 01' anothcr form it is desired nlso to detcrmilJe the Inetors whkh a.fJ'oet the proportion of loss, for cxnlnplr', ns run-of!' 01' ])('rcoln,te., or as soil eYflporation or trnnspil'ntioll from the plnTlt. It is also the purpose of the experiments to detormine the fnctors whielt nJ1'cet tho density of J'UIl-Orr or the amollnt of soil ",hi('\) is eaITicd. by n. given quantity of \\'ntcl', Such 1I,otors indude erop ('o,'cr, type fl~nd ehnmeicr: of root development, soil, slope, find minfnll, e1mrnetpl'if"ties,

',I~aeh of the I1bo,'e stud ips llIust;, of (,OUI'SP, be pUl'sued wilh ),prcrcnec to somc sperifle condition, snell ns the soil. t:q)(' 01' the dq:~rce of slope, or the ('I'OP growing 011 the iLrCH., and its tl'eH,tIllPnt. En('hrnul't nlso bC' dC'tC'l'rninC'r\ in, l'eln,tiOll to millS 01: rc('.ol'(\ed intensities, dUl'n.tioIlS, I1nr\, tot:tl amounts,

In nddition to tho n.hoyp studies it is (\psired to detel'lIlill(~ the most sn,tisl'uC'lorv 1I1('('hltnieal methods of (\ontrol\ing ('I'osion,

In ol'\lpl~ to pl'o\-ide. ini'Ol'llHltion 011 the lHcthods nne\. ('osts or C011MJ'u('ting t(,l'I'n,('ps, detniled time studi('s WNe madc during tl)(~ ('onc;tI'H('tion 11prio(\ nnt! the eflkicncy of the op('mtioll Wit,; impl'oYl'cl wl)('rc possible,

Obs(,),\,:ttions h:we becn, 1[1 progress througbout the last {) yefl.l'S to d(>t('I'mille llne! put into practi('('. the best methods of gull~' :111

16 'l'ECHNICAL BULLETIN 558, U. S. ])EP'l~. 01

17 SOIL AND WA'I'ER CO~SEIWA'I'ION INVES'l'IGA'l'IONS

CL'NTROI, 1'1.0'1'8, I~XI't]IUl\It;N'I' 1

The control plots known ns experiment 1 fire nine in number, seyen of which l1l'e one one-hundl'cdtlt of au nne itl SLr.C. the othet' two bcing, rcspeeth'cly, one iwo-hundl'edtltof nn Hcre and 'olle-fiftieth of all acre, l'epl'csenting the eompn,rison of slope length. The n.n.'rn,ge hUle! slope is n percellt. Tho HlCn,Slll'C'IIIP1Il; or ~;oil and water 10ssl;"

Flf:LO E.

Flht"Hl! r2~> 'ArrangeUlent or lysill1~ters Iltlll lhclr locntion in field l~.

from these plots is bitScd upon the entire e!l,tchmcnt of nUl-off and eroded. matcrin,l in conCl'ete bn,sins or tn,nks o[ sufli.eicnt size to retnin the gl'en,tl'st losses whidl it is estimn.ted will ocem during the comse of theexpel'iment. rfho plots aTe Ioeated upon the most uniform soil and slope which the 200 ileres of the fttl'm. afford. The profile has been studied in cletnil in the bbow,tory of the BUl'en.u of Ohemistry

l,l!!S!!l,p-:n--!!

18 'l'ECHNICAL DULLE'rIN 558, u. S. DEPT. OF AGRICUUPURE

and Soils and chemienl and physical nnalyses lutve been reportedelsewhere (5, 6).

The treatments of plots in thls experiment nl"C as follows: Plot 1, continuous COI'Il, slope length 36.3 fcpt, ono two-hundredth of an acre. Plot 2, continuous com, slope length ]4,).2 feet, onc-fifUeth of Hli U(,I'C, Plot 3, continuous corn, slope length 72.tI fect, one one-hundredth of un a(,l'e. Plot 4, rotation (corn, oats, und clovcl'), slope lcngth 72.0 fcct, OIlC olle-hllndromtion of organic matter in the surJ'ace 6 inehes of soil. 'rhe orgn,nic matter whiclt is used in nU except one trentmen t consists of 16 tons an acre of well-rotted stable manure. In one o[ the treatments the organic mntter consists of green sweetclo,'el' of a dry-matteI' content equivalent to one-hnl[ the dry-mattet' content applied to the other units. The treatments nre shown in table 4.

:Measuremcnts of percolate are made Tcgularly and not less frequently than once each week. NfeiLsurements of run-off nre made for each TainJall period and in a mn.nner similar to the method used in experiment 1. ThefnUow units in the series are ('ultivll,ted nnd the soil hnndled in the same mannel' ~1.S those units pln'llted to corn, with the exception that weeel seedlings following Inst cultiyn,tion a!'e removed by pulling as soon as. they make the!!' nppem::1.ll.t'e. Butrer trCl1.tmen ts t1.rollnc\ the extel'lOl' of ench umt n,re sl1lulnr to the trel1.tments on the units themselves.

http:triplicn.tehttp:ecrtn.in

19 SOIL AND WA'l'ER CONSERVATION INVES'l'WA'I'IONS

TABLE 4.-Trcfltment of soil on lysillleter.~, experiment J-l:J

Lyslrneter nos. Roil t~'(le Trentment

1,:1,5............ ..' .-"---- r;;:r~'UlU silt 1011111 .. FIlUOI". }'IIUOW plus Hi toilS /!IlIIIurn pcr lIere.

i,9. Il ..... __ .......... ,_. ._ _ ., __ ('orn. is, 10. 12............. ,,,.. ! _--:,(\1".-.,.,." ".--,- __ l'orll plus HlIOllS II/IIIIUro per ncre. 2,4, 6.... _................ _ ;_:: IIO() ~:.:.:._

J3, 15,17 ............... _... ....0 __ Blllegrllss sod 1-1, 16, IS.__ ____ ............ _I ....do____..... __ '" Corn )11115 J!nl(ln 1l1l1nUre (J!reen ~wl!etclo\'er

hll\~IU!4 dryrnttlll!r ('ontI.1tll equi\'nlent to Olll'hlllf of the IIlIlnurc lI[Jpll

20 'J'EcaNICAL BULLE~I'lN 5ii8, U. S. DEPT. O}

21 SOIL AND WA'J'Elt CONSFIWA'I'ION INYES'l'LGA'I'IONS

rate of intake of wILter into the soiL. In addition to 1,ho lysimeters (the first of which were constructed for this pllrpose in i030) nnd to the use of run-off

22 TECHNICAL BULL1!l'J'IN ijiiS, r. S. ])]WT. OI~ AOrtICGIlJ'URE

apply, of course, to those plots which 11n,"e like treatments, such, for example, as the corn plots of this experiment although the same procedure is followed with rderel1ce to nil of the expcriments.

,'rhen planting corn it is customary to pllLnt fi"e kcrnels of corn to the hill and cueh hill is Inter thinned to n stnnd of three pllLnts. Hows nre spaced 3 feet 11 pOIt in plots, and hills are spncf'd 3;~ feet in }'ows.

A sllmnutry of the results f/'(lIn June 1,10:32, to Decembcr 31,1935, is given in table 5. 'rho totuls am PI'(I!,;(,Il1ied grn,phictL1ly in figure 13. The individuolrun-ofl' nnd erosion rccords 111'0 giY(lll in tables 54 to 57. Plots 1, 2, nnd 3 gi\'e n. compnl'isoll of length of slope. Although the dif)'(lI'on('(ls in kngth are compnmti \rcIy slllnil and it is not expected thnt lnrge difl'CI'(lIl('('S ill run-olf will bo found fl'Olll su('h smull dHi'eI'enc('s ill slope length, it is intel'esting, JH,\rcrtheless, to 110te thnt the ]'till-Of}' is gl'en test from the sh()/t slope lind Jenst from the long slope but thnt the t(,lld(,IH',Y is r('\rpl'secl in tlw cllsn of e!'Osion.

FWt'ItE t:J ......... Hoil nud wuwr l(}s$~s JIIlIH 1, Itla!!~J)I\('l'lJ1ht'r 1, lH:llit ')'otul pn'clpitntion 102, 15 tnrlJll~; eJTecti\'o pre

T.H1LI:: 5.-.':5/U1/1//(llY of Tun-off (lnd trOllio14 I from control plol.~, c.rperilllclil 1, .f1l1l1' I, J!M'!, to Dcr. 31 I 19S/j

1.:\ V(lrn~u sJOI1\\ tI Jll'n'tillt]

J UIl~ 1-])(e. :!I. W:I~' 193:1 W:II j 1JJ35 TOlal 1932-35 I

iLellg~~l ;--.----~!-.. I---r --~-- I U1 HUIl,OI[ oI'lot I of I Tretltllllllt f. " f HUIl-olT i.. RUIl.UIT:..! HunotT :..! Hun-otf ., ....

no. S1 0J)C, ., brosloll ___ ___ ,J... ro~lOn __________ ~_ F..roslt)n~__--.._ -------.. ___ :F.. rosJOIl l~rOSlon t"' , J . j I ]ler , ! I "('r t I I ]ll'r ! I I p('r ' j per >j .\Wttuut1 l?('Il-, Here I \mount l?cu- n("r~ \IJl"tlllt t I](\u- :lefe '\JJU1Ullt J?en- '1('ro 1\n1(H1llt~ I:'eu- acre Z," "'ltv.3 ~ 'I" ~11\ 3 . stty 3 ,-- SltY Of , !':lty 1f____ 1__-......--__.- i '" '. I ! . '1 . ; . t;;

::: Fut ,;~~;-;:- -:;-r~;,:l-'J-;: I Ill.,. -L~~I.- .1 --~l'

24 'l'ECHNICAL BULLETIN f\u8, U. S. DEPT. OF AGlUCUVfURE

These results are Itpparently nssociated . with certain physical properties of the two soils. The eroded soil has a high degree of permeability when dry but u low total water-holding cnpncity. Small rains fire readily ftbsorbed, lat'ge ones much less so even than in the cnse of the normnl soil. li'urthermore it will be noted thnt the density of run-off from the eroded plot is commouly greater thltn from the normal soil. Thus the rcllttive erosion as well as run-off fluctuates with l'ninfnll nmounts and intensities and varies from storm to storm nnd from yenr to year.

'rhe result for the rotation of corn, oats, and clover, on plots 4, 5, and 6, are shown scpltmtely in table 6. In comparing these results it is necessary to keep in mind j,hat 1932, representing the first year of cropping treatment, corn did not, of course, follow clover. The 3-yeu!' period 1933-35, however, represents a complete rotation cycle in which eltch crop nppeltred in propel' sequence from tlltl beginning of this period. 'rhe tltble shows results for both periods 1932-35 ancL 1933-35. Inasmuch as tho latter poriod is of greater interest the discussion will be directed mainly toward this completed rotation eycle.

TAHr'fl 6.-Jiiffet:ls 0/ I'o/allon on 1'lm-oJ! and clo.~ion from control plots, by yearN(1.nrl /or ]Jcriorl 0/ operation, experimenti I

IA \'ern~e slope, \l percent]

Hunolf

IJ~~~(,.!I;:-~-1-9~1'-I--:----I-\I..-I'---'---"l-'j-

----------------- ------------

25 SOIl; AND WATER CONSERVA'J'ION INVES'l'IGA'I'IONS

TA,BLE 6.-Effects of rotation on run-off and ero.~ion from control plols, by years and for period of operation, experiment l-Continued

[A \' erugo ~I()pe, II percent]

HnnoIT J":rosion

Crup 3

HJ32-:J5 JlJ3:l-:Jli J9;12-35 1Il:la-:J5

Incites Inch C., ']'011.'1 Ton.,Corn._. __ ........: ......... , ............................ . 12. flS (l.85 89. :19 40.2-1 ants , ....................................................... .. Ii. OS 4.12 9.51 8. J5 Clo\'er.... ................................ , .............. .. 2.98 .08 .90 .10 Continuous com ......... __ ....................... _...... 11.80 1l.05 98.53 5f>.J{l

3 Hun.olT and erosion frolll cllell CIOII of rotlltlon for period of trclltnlCnl, in cOIllpllri~oll wilh conttlluollS corn.

The results ft'om the rotated cornland are undoubtedly a.bnonnlll owing to the fact that in the 1934 Cl'Op year the corn in the rotfttion was almost a complete failure. During this year very high temperatures p'cevailed and all corn on the fftrm which received orgftnicmatter treatments "fired" badly. It will be seen from tftble 5 that erosion on the rotated cornland in 1934 totftled 20.86 tons an acre, which was greftter than the erosion which resultecl from the continl1ous corn of plot 3 (19.48 tons per acre). The total erosion for the rotation in 1934 was 27.17 tons per acre, or neftrly twice that of 1935 and more than five times that of 1933 for the reftsons above indicftted. Even under these conditions the rotfttion obviously has been effective in reducing erosion. The measured losses of soil from the land in continuous corn totaled oyer 40 percent more tllftn the erosional losses from the rotftted cornlftnd for the period or rotation cycle. In 1935, the most nearly normal of the years in the rotfttions, erosion resulting from continuous corn was 2.2 times thftt of the I'otftted cornlftnd. The average annual erosion from nIl crops of the 3-yeftI' rotfttion cycle WftS 5.4 tons ftn acre in contrast to 18.8 tons ftn ftcre from the continuous corn, or less than one-third as much.

The density of run-off reflects the effects of the rotfttional treatments as shown in table 5. It is seen that for theentire rotation ftn average of about 2 pounds of soil per cubic foot of run-off resulted from this series of rotated plots. On the plots in continous corn, however, over 4 pounds of soil were carried in each cubic foot of surface run-off.

Striking results in the control of erosion are shown by nlfalfft and bluegrass. For the entire period 1932-35 ft total of only about IX tons of soil per acre was eroded from these ftlfalfa ftnd bluegrllss plots. Over 90 percent of this erosion occurred during the first year of the treatment or during the period when the vegetative cover was being established. Following this first year the total erosion from the alfftlfa plot was only 0.07 ton per ftcre and fro:n the bluegrass plot 0.12 ton per acre.

These crops are less effective in reducing run-off than in reducing erosion, ftS may be seen from an exftmination of table 5. Erosion on land in alfalfa and bluegrass was reduced to about IX percent of that from the same soil type in continuous corn, but the run-off was reduced only to about 30 percent of that from corn. In brief, the alfalfa ,and bluegrass have very greatly reduced the density of

26 'fECHNICAL BULLE'l'IN 558, U. S. DEPT. OF AGIUCIJIJI'UllIn

run-off hut the total amount of run-ofr itself is still n.pprecin.hle. These fncts have a fundamontnL bearing upon the dpsign' of stripcropping tren,tmen ts discussed in later ]Jnges.

OVJ!'o 1.75" PEg HOUQ

OVEQ /.50 PI!Q HouQ

Ovt:Q. 1.25 Pt:~Hovtl.

OVEt:lI.OO P~QHoCJQ

OVI!t:l.50 ~QHovQ

OVEQ .25' .P~QHouQ

r I

OvEQ.OO..r pe"'HOVt:lr

I () sI I o S

I o

I I I o S

I I I I I 10

/0

s

IS

/0

s

JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC.

J"muHB H.-Seasunul occurrCI1l'tl of rai II fall fur }U:{2-:Jfi, dh'id(~

27 SOIL A.i~D WA'J'En. CQXSEllVA'J'ION INVESTIGATIONS

4-year period) that the hCflyicst mins occurred during the mont.hs of June, August, nfa.y, lind ,Jul~y TPspeetiveiy, lind thnt April flnd September nrc, nlso months whi('11 nOl'mnllv huye l'nins of suflieient intensity to pl'odu('c 1'I1ll-ofL ]n figul'e 1'5, JlOwe,'('I', it is S(,('1t that the pellk run-off o(,curs at difl'(lI'cnt s('lIsons 1'01' difl'eJ'('nt vegetatiye

8LIICcJPASS I

.., ft ..-- 1J____ I I

JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC.

1'1Q1'ln: lI;.-iit!lL~onnl oc'CUrrim('c 01 fllll.;)IT lor cxpcrilllcnL 1 control plots for 193.'1-35.

COYNS and thnt, for cxample, thc gl'catcst run-off from blucgmss and nlfnlfn, oC('UlTNl during J:\I\UlIl;'T, when the ground is frozen. TIl(' greatest run-ofr from 0:1 ts 1'('stdted from rains oCCUlTing in nfllY June, August, September, and October, however, produced npprcriable qu:mtitiesof run-ofl'. The leilst Tun-off frout this crop ol'l'urred during July :wd the Inttcr pInt of June, or during the period fit which the plant hild rCllchcd lllHximulll growth. It is obvious, llOwcver, that the protective e.fl'cets 0f oats me of eompamth-ely short duration. In the case of corn the gn'atest run-ofr hns o('('urred during JUlle. ~ln.y, September, and October, hn,vc nlso been months when rather

15

28 'J'ECHNICAL BULIJETlN 558, U. S. DEPT. OF AGRICUL'I'URE

largc quantities of run-off o('('urred. During July and Alwust, on the othel" hnnd, whkh nrc months providing eomparative1y good ('oYer, th('rc WflS less run-ofr thnn in June nnd September, the months w\lPn protrdion WIIS It'ss ('ompl(~te. .

Knowledge of the seasollal o('eurrcnee of erosion is likewise of great prncticIll importance, lfigure 16 portrays its varying seasonal occurren('c, If, is s('('n lit once that wherens appreciable qllnntities of run-ofl' o(,(,UlTed from hluegrnss, nlflllfn., and doYel', thc erosion from

o

I. I

AL/"ALrA

--+--------.~-------.------__1

'" S

CLOVE:Q

--+--.--.--~.------------~ o IS

II>

OATS si;;'..___I-_______ _____~'____~____j 0 ~ .."

20 III ~~ 10 "l r .1~

COQN ..... ~~r.~~o~~~h~on2~-~--------~-----~---~-------~ O~

'"'t ~I:)

'I .!'SI:)

~~

;" 30

20

ZO

1$

10

$

L-~~~-~~N~~~~=~l~~~~~~~~~~~~~~~~~~~~~~~~~cQ

1-~lorHfo: 16. 'ft.'.asUllnl O('('llrn,ltltll "rerosion qll C~I>criJ1l1!nt. 1 (:outrnl Jllots ror lH:t~-:J;'i.

Illlld with tllP:SC ('rops wus extremely slight at illly senson of the year, In the ('nsc of onts the gr'l'Iltcst erosion oe('ul'red during :May, which wns also the 1I10n tit during whieh the grcn,test l'Ull-off o('eurred, l?ollowing this deyciopmcntul period in the ont erop, howevcr, vcry little erosion o(,(,UI'l'ed in su('('ccding months, In the cnse of the ('orn, erosion parallels c1osC'iy in sensollal o('('urrCIIee, the run-off losses, .June iF; the month of gr'cntest cl'Osionallosses with :May Ilnd September next in order, It is npparcnt !IS between 11 cultivated crop, such

29 SOIL AND WNI'ER CONSERVA'I'ION INVES'rJGA'I'WNS

ns corn, and a CI'OP of dosn Yegetn,tion, such ns oats, that marked differenc('s in protl.'rtiyo efTec'ts mllY bo ('xpc('ted, Thlls the onts provide a gl'cntc'l' Pl'Ot(,(,tion ngninst el'osion thnn ngninst l'un-ofL Corn, on the othel' hnnd, provides T>l'otC('tiOll pl'imnrily to the extent of ('unopy inten'eption Ilnd the water whieh renches the lund sUl'flt('c still hus nn, erosivo efTcet,

In addition to the efrl.'ct 01 close-growing ('raps und cunopy intel'('eption on run-ofl', thel'c is n150 thc fnetor of moisture usc by these ('I'OPS, No doubt the wlthdmwal of WlttCI' fl'Oll1 the soil by the growing nops pl.'l'mits 1m in(,I'l'l1sc of inJHtl'atio II , e5peeiltlly where rnins follow in close SII(,(,l.'ssioll dUl'ing the gl'owing SPHSOll. The relutive efl'ediv('npns of this i'uetol' in difT(,I'C'nt (,I'OP5, however, was not mitde l~ part of this study,

UN('ON'rItOLLED VAHIATION WITlIIN 'l'IIE EXP}~IU~rrJNT

His importunt to know the, cxto{t,/lfl.'( Gfll"Jm~ \I. an l'''.'.!I; :.!.~:! l:...Jt).M,

111.HII 73. ttl I~j. :'~I ~""nl.,,1. Iii 19.-11

25. U:{'''S.lI'(lL:!1 :!. it)

3111.25 -"01_ -17.1l3 ,(NI ~~J. 76 IS. 11:1 'rUlnl: :1I.O:l ~,O~1. 10

I

30 'L'ECHNICATJ 13UI"I~E'I'IN liM;, U. S. l)]~P'I'. OF AG1UClJI11'UUE TAIlI,}) 8,-C'oll/p(/riso/l,~ oj colloidfll conlelll, 'IIwistul'C equivalent, lind d'i'~7)l!l',~ion

ratio 'in plol;; .'3 lind .1 'in COIll'iI/.'/I.Otl,~ alld 'rotfllt'd corn, 1'{'o}}(!clillely

('olloid by "''''er ~1"isll1r" 1!I!uh" IJ l~persl(JJl rll: I"\"Ilpor nhsofJll ion :llent.. HorIzon

} Jt'rrrlll J~errrl/t '~

31 SOIL AND WA'l'ER CONSERVA'eION INVES'I'IGA'1'IONS

taller thnn the corn on the continuous plot while the cO~'n on desurfaced soil was very much shorter. In the ahnormal yenr of 1934., 1lOwever, during which senson tem peratures as high as 114 F. occurred several times, the com which followed clover did not produce ns much growth ns continuous corn. After July 9 this corn fired so badly that growth was even less thnn that on the desurfneed plot. In 1935, which WitS n senson of normn.l growin~ conditions, the rotntion corn WitS consistently tn.Ikr than the contmuous corn, nne! this in turn produeed gr'eater growth thall did the corn on desurfaced soil. The growth curye of the btter fell ruther' shn;rply following the llleltSUl'Cment made on ;Tuly n.

300

ClIO

""" - llCONTINOlls CORN uo OROTATION CORN

CJGl?NTINOVS CORN-::-,'00

" (OESU.eF,4CliO) Ii~",o ~

~160 ~ I!!''''' ~ ~/20 J... I~IOO l/

!!! s..

~

., !

32 'J'ECHNlCAIJ BUJ.JLE~l'lN 558. U. S. DEP'J'. OF AGH.ICUL'l'UUE

slope is significantly less than the moisture content of one or the other of the longcr slopes. It will be recalled thaI; the data on run-off show more Tun-off from the short slope than fl"01ll the long one. This type of study docs not penni!; the ac('u1llulation of as lal'ge an amount of data as is desirable without the expenditlll'e of exccssiye sums in order to make VCl'y frcqucnt slunplings, The trcnd, however, seems to be sufidently pronounced. to estahlish rather definitely the fnet that wll('re othel' ('onditions me idcnticnl the soil-moistlU:e content benrs nn illyel'se l'dn tion to the amount of run-ofl'.

TAIIl,~l fl.-8oil-moi.slllrl' d('t(,I'/I/i.l/(llion.~ -in field E, cxperiment f2

1'!ot 1I1l. 1- W:!2 I J!J:\~;-r-l-U:-H--;---JO-:lf-'-. ----.-------... ---.---' --..._---

]1 PacelliPrrcCII/CQl1til1UOUS corn ______ ... 2(1. "0 10. II

_.do._________ .._. ___ __ 2.5. no 211.02 _.. d". -... __ ..._______. 20 .J-I W.5a HOlllllol1 l .............__ ... . 27.76 1tl.11

110.1 .,", - .....-- ... . '.!t.SO \11.28 "'01 IfI,j!J... ,h .I ...... --.....---. '1',\llal(,,- ............. ,, __ ~~:iH IS. O'

Hh)('!(fOSS ..... "' ....... .. 2'\.1)7 20. :11 Continllous ('01'0 (t.'I'Ofillt! ~ ~j* tiS ~l .. 75

--~--'-------- .. ._-'----'- .._----t Corn, OULS, ('l()\rer on [llnl~ ,i, 5, nud fi, TP't!lN't!\elr. in lH:t2; plots 0, .1, nnd [, jn W:J:l; plots 5, HJ and 4 in

WI4: nnd plots 1. 5. IHIII Ii In 1V3;'.

'L\lll.g 1O.-CO/ll]Jari,~on awl .~i(JnifiC(l.lIcc of lI/CIIII r1 ilTrrenccs 'in soil -moi,~/IIre in 111o/s of Jielll h" e:c]ll!rilll/'llt J

Coutparison

~.-:-----:----

I HI:!:! I!i:l-i

!'(((,fIIl

11;'. 2) ~~(~).\\~~~o.'~~:~:~:::::::. ! +~:l~~ ..... do, ... ~,"_ .. ~~ ..... ~"~~",. -.fill

I .HO)UIl.!.1 corn........". 1 -1.:12 Hotn\('d nnts .......... I tt.11-I Hatn)('d clnver --. ....... Ita. 50 AIf(\IC,L __. . ... ) -I.no Hlu~l!tnl~s~ .... ~"".. _.. _~", 1-:.t1:1 ('ontinIlQIl~ corn (eroded) I -I.bl

, HOlnled OllIS. ......... ) +0.211 ; HOlfil,'d eltJ\','r ......... ) +t ....2 \ AlfnHIl__ ......... -.2~

72.0' Hhh~~ru~!'. ~ ... __ .... ,_. -.sl - C'oulinllOlls NJn1 (ernt1~d) -. t!)

Hotnlcd c10\'cr .......... -i.I,1 AICnlftL., .... __ . __ .. , . ) -li."1 !lIt!l!Rr:ls" ..... __ . . . .. ) - 07 ('()l1finunus eOI'll (crocted) 1 -11. 15

.,\ICnlf" ... ' . 0' .1-5.10 (\llle~nlss.... -- .... ') -T!.n:lI, ('ont.lnllllll$ corn (erod('d) j') -5.01 t Jlhll'grnss .. ,.... __ ..... -, fla! ConlinuOlls corn (eroded1- +. on

... do ........ --'. t '+.1i2 .- ..-~----_.

) SI~llftictlnt ditT"rcll('('s-llldhldunl II"tl'rlllillnlioIlS teslml I!y slutl,'nt's methods of pairs (Hl:l2-!14) IIl1d IIllnlysis of vnrilU1CI) (11l:15) 10 dc(erllliric SighillcIlIlCO of IntTCrell!:e h"!\\'",,11 soll111oi;llurc ill dilTerell1 plOlS.

In the CflSC of ('lovcl' in rotation, the moisture content of the soil WalS lcss in 1\11 4 yeal's of thc cxpcl'imenL t1ln,11 fo!' soil undel' ('ontinuous corn, The moisture content under ulfulfn, ",us significuntly lowel' in

SOIL AND WA'rER CONSERVATION INVESTIGA'l'lONS 33

this plot during 1933 and 1935 and about the same during 1934 as in the continuous corn plot. In 1932 it was higher under alfalfa than under corn but this may be due to the filet thnt the crop had not as yet developed fully. In the comparison of bluegrass with continuous corn, the moisture under this close-growing crop likewise wus lower in 1933 and 1935 lind about the same in 1934 as under corn. In 1932, however, it was higher tlUlD under corn. The oat plots, likewise, showed. less moistllfe in 3 of the 4 years of the. experiment.

These results undoubtedly represent the bnlance between the losses of surfuce run-off and transpiration. I...ess run-off resulted, as shown previotlslr, from the close-growing types of vegeta.tion such as oats, clover, nlfnlfn" find hlueglftss thnn from the row-spaced corn crop. However, it uppenrs obvious thllt, in certain yenrs at leust, the transpiration losses from the close-growing C1'OpS exceeded the net savings in precipitation owing to reduced run-off from the same crops.

The results !llso show n. slightly higher a.yernge percentage of moisture under the continuous corn growing upon eroded soil than under the continuous corll growing on norml11 soil. This is probably owing to the highel' content of cliLy lind colloid in the profile of the highly eroded plot.

CHOI' YIEL[)S IN EXI'EHIMENT 1

During 1933, the first ~Yellr of corn on dover sod, the yield was 73 hushels an acre in con tmst to an uyel'l1ge of 5f} bushels for the continuous corn on normul soil. The yield on the eroded soil was only 1i.4 bushels un nero.

In 1934 the corn in rotation fired, und fuiled completely during the gren t drougb t. Corn on normn I soil wus prncticaUy n. fnilure, but, nev'ertheless, yielded from three to five times more than the corn on eroded soil.

In 1935 the rotllted corn totnled 43.5 bushels an flcre in comparison with nn nvernge of 38 bushels for plots I, 2, lind 3 where it hnd been grown continuously on 110rl11nl soil. The yield from the eroded plot wns only 4.29 bushels nn nere (tnblc ] 1).

TA IlLE 11.-Crop yields I froll/. control plots, experiment 1

1\~12 I!tl:! J:J35

Plot Trelltrncll~no. Wlr or IInr or lIllY or IIllyorGroin Ornin (lrain C1rninstover 1 S(.O\llf sto,'cr stover

pt.~r nero per n(.'re per nero per neroI)Cr nero per ncre per nere pcr ncre

--- ---_.- ---.--- -------- II'Mhfis 'l'on., JI'Mhd. 7~0ll.t B'Mh(l. 'rOIll( Bush". 'j'on .

J Continuous corn 21.4:1 5i. J.I

34 'l'ECHNICAL BULLE'l'IN 558, U. S. DEJYl'. OF AGRICULTURE

The yields of the other plots of the cxperiment sho,,' practically normal growth wn.s secured for the years exclusive of 1934. Dates of CI'OP plnnting and. harvesting nrc given in the detailed log of treatments (table 62),

NITHATI~ DETEH~IINATJONS OF HUN-OFP

Nitrate determinations of the run-off hn.ve been made by the soils section of the department of agronomy, IOWIL State College, The results tn.bulated for this shol,t period were too inconclusive to warrant much discussion at this time. Obviously, a longer period of time nnd a larger mnss of dntn. are nccessary to dmw nny conclusions from this portion of the study sincc it appears thnt both frequency nnd intensity of l'ninfnll, lLS well as plot trcntment, affect the amount of nitmtes which are carried from the plots.

CHANGES Ii\' SUHFACE CONFIGUltATJON OF PLOTS

At lenst once eneh senson, nt fL time when soil conditions are stnbilized, n. scries of surface elevations lire made on elLeh plot of the experiment. These elevntions nre detel'mined at I-foot mtervals along the length of the plot and nt duplicate points ncross the plot. The dat:t thus provide n. menns of determining the chnnges in surfllce configumtion whkh 11I'e occurring upon the vn.rious plots during the course of the experiment. The differences nre best seen in grnphic form nnd are included in figures 18 t.o 21, inclusive.

In these figures the devintion of the various nverage longitudinal determinations hu.ve been plotted in compnrison with the menn slope of the experiment.

It is seen n t once thnt some very striking differences in plot elevation hnve nlrcady occurred find thnt these differences in elevation appar(lntiy are correlated with the plot tren.tment. The zero points of position upon the churts represent the fixed lip where run-off leaves the

l)lot. The figures sho~v the piling lip of soil immedin.tcly above this ip. Figure 18, representing the three lengths of slope o'f continuous COl'll, show It rather marked reduction of elevn.tion at appro~imately 90 to 95 f(let above the lip. Another tendency toward cutting lIpp

-.20

+.20r------r-----,r-----,-----_.------~----_.------,_----_,

A 0/933 &/935

+.20~----~--.--~----,------r-----r----~----~'~----r-I----~----~-----r-----r-----r----~-----,

o

+.10

~ o

-:/0

.B 0/933 M/934 4/935 L I

90 100 //0 /20 /30 /40 ISO+.20,---r-----,---..----,-----,-----.,.-----r-----, POSIT/ON FROI'1 ,L/,P .AT ,LOffER....

.liNO OF ,P,Lor (FEEr)

01933 M/934 4/935

...20 ~--,=_-__:,"::_-___::',"::_--::'---::'---::'-_.!.~ _ o m 20 ~ ~ ~ ~ ~ ~ PO

35 SOIL ANn WA'rER CONSEHVA'I'ION lNYESTIGA'I'roNEl

+.20

0 ..o

01933 -1934 AI9as A

~20L-----L-----L-----~--~----~----~----~----~

01933 -1934 A/93SB

I

+.20

o 0

...,/0

01933 -/934 A/93SC

-.20 a 10 20 .30 40 SO 60 70 80 POSltlOIll FROM LIP ,.AT '-OWER. ENP OF PL.OT (FEET)

Fllll:ltt: W.-VurlntlOIl ill clemtioll from menll slop" or CXIM!rimcllt I: A. Plot -I. l!I:.12 corn, ml:l ollis, 19:H clo\'er, 1!J:15l'Orn B, plot 5, 1002 outs, 19:13 clo,'er, 1 U3h'Orn , )U35 Ollts; c,.', 1)1010, HJ:I:! clover, )\}a:l corn, 19:14 onts, 1935 dover.

36 'l'ECHNICAL BULLETIN 558, U. S. DEP'l'. OF AGRICULTURE

+20

o o o 0 0 000 0 o 0 00 0 0 0 AOoO

00 0 0 .A A 0 0 AA A

o .. " 0 000 ~ ~AAtU\~ loA A 0 0 00 A t. t.r~.6AA

.... OOOAAII A 0

l_~~O~~____~b~~~,~,~,~,_~______.A_~A~77.~~~~___~~~~--------------1 0" o~ ~"':'A 1 ne" .. h ..Il '\,

A \L/ne represents meun s/op" .~:; cr'""penme'nt,n I!JJ.J~U1(}rercent

-:10

A 01933 x/934- "'1935 ~20L---~_____L-1___~1____L-__~____-L____~__~

'--'---,--~~-_r_--_,_-

.. .'

0 \ LIne represenls meO'I1 slope.. of'expenmelll In 1.9'.9.'10pe/'ct:/11

-:10

B 0/933 x/934 .t../935 ~20

1

0 10 20 30 "10 50 60 70 80 POSITION FROM L/P ..AT LOWER. ENP OF PLOT (FEET)

FmlJln: 20.-VurlnUnll III CIC\'lIllolI from melill slope of experiment 1: A, Plot i, nUnlfll, 193:l-3.;; n, plot 8, hluegntss, lU:l:l-:lfi.

+.20

i::' x+.10 x~ (. L/ne represents mean s/(}De

\ or'e'-"penment,n 1.9~.J'.940 pen:t'IIt .. A~ OA .4

OA .1:.~ 0 xA 00 'Ai:: o

4 'It:'~ o A'A AIII

o

~ -:10 0 0 A,,;4A S. 4AAA AI:. "aOOo A .....a

o x 0/,933 x1934- ,"'1.9351 0 0000 1 1 I ~20~----L-----~-----L-----L----~----~______L-__~

o m ~ ~ ~ ~ ~ ro ~ POSITION FROM LIP ..AT LOWER. ENP OF PLOT (FEET)

FmURE 21.-Vllrlntloll In elevlltlon from meui, slope cf experiment 1: Plot 9, continllolls corn (d

37 SOIL AND 'WA'rER CONSERV A'l'ION INVESTIGATIONS

LYSIMETEH lIlElASUUElMENTS O~' I'EUCOLATFl, HUN-OFF, AND EROSION

It is obviously important to know the I'elation between pl'Ceipitation and Yltl'iotls fonns of loss of water from the soil. The ('fl'eds of various tl'Clttments as they may be rcllLted to water intnke, sllJ'fuee

FALLOW COON

80 r-

(~

70 I ~

.11 In ......

60 I-- I-- I- ~ (I')

~ )f" ~ ~

38 TECHNICAL BULLETIN 558, U. S. DEPT. OF AGRICULTURE

The special type of lysimeters which are used in this study have provided some data on these items. Table 12 gives a summaIy of the results of measurements of percolate, run-off, and erosion which in the case of the first 12 lmits extended from May 5, 1933, to December 31, 1935, and covered a period of practically 32 months, find in the second 12 units, extended from July 1, 1934, to December 31, 1935, a period of 18 months (figs. 22 and 23). While the time of operation may be

60

MAOSttA L SHCLBY

50 c~

MA~

~ 40

~ I ~

N - ~ ~

~ ~ M It)

M ~EO

~

10 \g qj

\g

~ f:; ~ Ci i3

~ ..J

I- ll) 8 -.j

~ I- ~

l- I': ~

g -J- C\l 0

~ -- III0 V)..J 0

-.j

8 CI ~ aI-

~ C\ f2 ~ 10 ~

I- ~ Ol I" (\J ~I- ~~~ ~~ o ~ ~ 0 ~ ~ ~ .~ ::> &1 ~ ~ N

Q Q ~ :/ Q ~~ o ... ffil~~~~, ..... I~ , ~ ~LaJ,~ CI) q,\0 ~ I'i~ .. iii () ~ I.J ~ III (j/0 IJ~ Q; ~ Il:

Q. ~ ... ~ Il: 20

.DI:JPQSITION Otr Oci.cCIPITATION IN LYSIMt:.Te:as MAQtiHALL li SHELBY 51LT LOAM.

JULY 1934 - JAN. 193

--------------------------------

---------------------

SOIL AND W NfER CONSERVA'rION INVESTIGA'fIONS 39

subjected to the analysis of variance. A detailed log of treatments follows table 72 and crop yields are given in table 73.

TABLE 12.-Su.mmary of percolate, Tltn-off, and erosion I from lysimeters experiment 1-B

[A vcmge slope. 9 percent1

May 5-Dee. 31, 10:13 1034

Erosion and Erosion nndPercolnte nnd Percolate nndLysime donsity o( densityo(Soil and treatment run-olT run-alIter n05".'2 run-olT' run-olI ,

l?erco Den Perea Hun- \ Den-Inte 1~1r- Amount sity late olT I mount sity

/r",. /11.,. 7'01/8 LIlY. /11'. }II.!. 7'07lS D".Mnrshnli (fnliow), ______ 4.20 O. GO 20.01 2.17 I. 07 7.02 23. OS 1.00 Marshali (fnllow)'+mn

mlre__________________ o.:lO 0.09 17.8.1 1. 62 2.4:1 0.00 10.6.5 .08 7,9,11 Mnrshllll (corn)_________ .711 4.07 HI. 70 2.67 . I.; 4.45 13.4" 1. 67

8,10,12 Marshali (corn) + lIIanure__________________ 1.51 2. a:l 4.43 1. OS .19 4.40 3.62 .4.1Marshall (hluegrll~s) .. __ ________ ________ _________ ________ .0113,15, 17 3.81 a.29 .47

14,10, IS Marshall (corn)+swectc;lover_________________ ... ____..... ______ .. '" '''' ___________'"'_________ ..... 0.30 11.24 .98Shelby (Illlowl'______________... __________________ ._______ . ISW, 21, 23 4.SS 8.57 .97 20, l:!, 24 Shelby (fllliow)' + 1II1ll1ure __________ ______ . _____________________________ .:11

4.00 r..48 .77

'rotul, 1933-as

Erosion nncI Erosion nIHIPercolate Ilnd Percolnle nndLysimc density o( densityo(Soil Bud trcatment; runolf runolfter no...:;.2 tun.olT 3 runotT'

Perco Hun Den- Pereo- Hun- DenAmount AmoullLlate olT sity lato olT sit,

111.,. Ins. Tons Lb. IllS. h18. TOllS Lb,. 1,3,5 Marshall (fnllow), _____ 7.07 o. on 12.96 0.7U 12.34 23.61 02. OS 1. 45 2,4,6 Marshall (fnllow) '+1IIanuro.. _________ .. _______ 11.29 5.52 4.02 .40 19.02 1i.6t 32.52 1. 02

7,0,11 lIrarshnll (corn)...______ 4.58 0.7-1 U.07 .74 5.50 15.25 42.22 1.52 8,10,12 lIfarshnll (corn) + lllU-Iture..... ________ ... _______ 0.0.1 3.02 2.80 10 8. a.5 10. on 10.90 .66

13, Hi, j; Mnrshall (bluegrnss) .... 1.10 2.78 1. 58 .3t 1.11 0.59 4.87 .41 14,10,18 Mnrshall (corn)+swcotclover_____ .. __ ......____.._ 3.2,; 7.40 9.74 .72 3.2U 13.71 20.98 .84 Ill, 21, 2:1 ShelbY (fallow)'.________ l.ffi n.t!! 8.29 .50 l.Ull U.OO 10.87 .00 20,22,24 Shelby (fullow)' +mil'

Ilurc .. ~ ...._.. ~ ___ ., __ .... ~ .. _ '1.3:1 6.72 4.86 .40 4.67 11.37 1l.34 .55

ll'rc('ipitlltioll (inches)

40 ~I'ECHNICAL BUJ~LE'J'IN 1558, U. S. DEPT. OF AGRICUVl'URE

silt loam, the application of manure increased percolate from 1.98 to 4.67 inches nnd reduced run-off from 14 to 11.37 inches.

These effects nre striking, pnrticularly in consideration of the fact that the npplication of the treatment was confined to the surface 7 inches of the soil profile, whereas the measurement of percolate shows very marked incrdase throughout the entire 3-foot rrofile. The Shelby silt loam, which bas a rather impervious subsoi , was affected to n greater percentnge degree even than the Marshall.

The insignificilnt differences in nm-off from the Marshall and Shelby soils most probably are due to the relatively short length of slope (3 feet) and the consequent short-time interval for run-off to OCCUI. On longer slopes the more permeable JvInrshall soil would be expected to show a larger totnl infiltmtion and less run-off than the less perlI1ciLble Shelby soil ns in fact is indicnted by a compalison of the data of the Bethany, Mo., stMion (Shelby silt loam) with the data 'cited from expcrinwnt 1 above.

Accompn.nying the reduction in run-off cited ll,bove there have heen eqm greater l'eduetions in soil losses. On the fallow Mal'sl1l1U series the 111l1nure treatment reduced erosion from 62.05 to 32.52 tons PCI' ncre. On the COl'll series of the Marshall silt loam the manure treatment reduced erosion fl'om 42.22 to 10.90 tons per acre. On the Shclby sedes the treatment reduced erosion from 16.87 to 11.34 tons per acre. SeYern.l interesting fncts arc disclosed by these data. The reduction in rurl-ofr in the com series is proportionntely greater than in the fallow series. The rodu(,tion of erosion in the com series is likewise proportionately grenter than the reduction in the fnllow series. However, wherens the run-off ill the 1l1nJ'm'ed COl'U sCl'ies wns reduced hy the treutment to 66 percent of its check treatment, the erosion in the sllme series wns redu('ed to less than 25 per('ent of its check trelltmont. It is delll', therefore, thnt the mnnure trelltment is producing sevel'lll difJ:eren t effects: (1) An effe('t upon the soil itself due probably to nn in('rellsed pOl'Osity of the surface soil; (2) an effect upon the plan t in prod ucing a more yigol'Ous individual with larger leaf surfllc'e which ill tUI'l1 permits grenter interception of rainfall by the canopy; nnd (3) 1L plnnt having a more vigorous root system wbicll apparently hns a pronounced effect in reducing the density of run"'off.

These effeets upon the density of nm-off are pronounced in the fallow series on the },,fnrshnll soil, the manure treatment reducing the density of run-of I f!"Om 1.45 to 1.02 pounds of soil per cubic foot of Tun-off. In the COI'U series it reduced the density from 1.52 to 0.56 pounds of soil pel' cubic foot of run-off. The efl'ects upon the Shelby soil were not so pronounced, the reductions being from 0.66 to 0.55 pound of soil per cubic foot of run-off. . A fnidy dose approximation of the effects of the treatment on the vapor losses may be arri'Ted at by cnlculating the totllliosses in the forIll of percolnte and run-off nnd subtracting the sum from the totnl precipit:1tjon. These results are shown in table 13. The total vapor losses from the fallow series, of course, represents the totnl soil eYnpol'l1tion. The vnpor losses, however, from the COI'U series represent the combined loss of soil evaporation and tl'l1nspiration from the corn itself. It is of interest to note thnt the addition of manure did not incrense the vapor losses in the fallo,Y series. However, the vapor losses were increased in the corn series and this increase may be attributed to greater total transpil'l1tion from the manured corn.

------------

41 SOIL AND WATER CONSERVA'I'ION INVES'I'WATlONS

TAJlU; 13.~811mlll(/I'Y oj /('ot/;'1' relation,s, lys/:llleler experimcnt /-8

j)otcnI'!!T(.'O- \'apor linlh'l'oil lind treutrnent 1;~~1~:;' Rnn'olfl InwJ loss u'''nilnille

waH~r

Marsh'lll: Fnllow, ch~ckl__

42 TECHNICAL BULLETIN 558, U. S. DEPT. OF AGRICULTURE

Comparing the erosion for these same treatments it is seen that in the fallow series the totnl soil losses amounted to 191, 146, and 114 tons per acre for the check plot, the low rate of mnnure, and the high rate of manure treatments, respeetively. These same treatments in the corn series gave erosion totaling 77.5, 32, and 18 tons per acre, respectively. Thus the control of erosion by the application of manure hilS been very much greater in the corn series thnn in the fallow series.

zoo 190 190.7.1 so~.EROSION-TONS' PER ACREleo ~ ORtlN-O,

TABLE 14.-Summary olTl/n-off (/nd crOldulI,1 experiment S, ,\lIg. SI, 19.0gB, /0 Dec. SI, 1.9S5

fA \'em~e glape, 0 Ill'rccnl I

Allg. :11~1)e('. al. m:l2 .:;;;;;-_.,. "'r H1:H lU:l5 '1'01111, JUa2-35 Ul o1----,- ------:::-1 ....Plot j 'I'rontmcnL HUIIolf Em. HUIIotr Ero'l Hlln'()IT 'Ero- HUII-oIT HUII-olf }:ro t<

no.' I sion sinn . ,.' ~ sion sion ~---;--- sion-~------. 1 per IJUf, per p':;r pcr

I)N1 I,l)on- Den ~ JH.'fO \mouut [1?Cn. Uere J -\mount II!rm. . fipre ilt'ra .Amount nero1.,sity J ~ .:1I \3 r SII \. 3 sity 3 t:;_~'I ("IOUII I " . I ..; AII=,S:':' --I '~--,--- ;'Iches I~I' j

'nella Pound,., ~ni1ls Incll(.~ J)oullf/~ Thu ~l'''1J.'l illchf.'1 . J'oullIl . ." 7"on.", Inchr., Pounds ~ron., ('orn+hi~h swcnldo\'er '" ..... " 0.511 a.1Il a.73 LaO I.W LOO 1I.1!1I 1.21 ::!. Ii 1.. 37 I. 27 a.14 4.25 1.11:1 12.5.1 i

_ __2 Corn+low swcctclo\'cr' _ ,~. .au 2.U.i 2.10 I..~O 1.:12 1.31 1.0:1 2.4ti I 4.01 2.0:1 a.02 11.14 5.20 2.32 22.16 3 Corn+16 tOllS mUllure per acrc ........ . ~:! !I.14 :1.73 1.:10 I. 22 ~W .s:! I.@ 3.70 10.-17 3.4:1 2.88 17.00 ~ 1 00rn+8 tons IIIlIlIurO I"" lIero. ~ !17 IUr. 1.:10 2.-11, 1.1:l ~m I:~~ ~: ~i I 5. \~I 2.:11 4.IlO Ifi. ;7 O.:t~ 2.79 32;00 C':I 5 Corn. check." .... " . ... '''.,. .SO Ii. 06 11.22 :t 75 a. i;i ~~ 2.18 ,1.4:1 II'.M 2.-1-1 5.21 2:1.26 O.2n 4. no 77.41 6 Fuilnw+high sweetdo\er'.". ".". .:10 5.00 :1.5(1 :1.07 ti.75 ~m 4. S7 5.0 ii(1,40 1.61 a.42 28.1\0 12.93 5.12 120.!lt ~

FlIlIow+I()\\" sweetclo\"cr '"" .40 S.II iI.Hil .1. 73 5.111 50.71 -1.:\4 7.al 57.55 .1. Oil 1.97 ar..lIs 1:!.47 0.15 1,.0.29 8 Fnilo\\'+16 Ions llllUlllro per IIcro, :10 G.a5 1. IS :1.:11 I' ~OO 4.11 6.IH 51.~:{ a.1i:l 5.71 37.7; 11.-15 5.,19 113. Il!I ~ !l Fnlio\\'+8 Ions mllnuro per ncre .:12 1:I.af. 111 1 ;1 n;l! ~~ 1\.19 1i.:1I! 51l.5() I .1. ,Ul .1.25 41. !K) H.GI 5.49 145.86 ~

10 Flllio\\", chee k . t25 n, Ii lii.a2 n,ns I 5. ~'I (it, in I 1,!11 '.1I1 ! 0:1.0:1 ' fl.:!-I 5.01 I 47. fil 17 .';1) n.ol IW.n ~ ~

1 Precipitlltioll (inches) durin): lhiscxporimont WIIS liS follows: For 1032, lolnl 15.\)2, ofTectivo 10.40; 19:1:1, 101111211.88, olfccth'o IS. I!!; 1031, toIlI121.12, eITecti\o 13.0; 1935, totlli 32.62. o ....

e!Tecth'o 22.89, 10tnl fur entiro periolI 00.54, elTeeth'c 65.27. 'All piots of osperimelit not in operation untiIAug. 31, 1932. Z 3 Pounds ofsoii per cubic fool of wnter. .... , Greoll swcetdo\er. dr~mlltlcr eOlllont oqulli 10 high rule of mltnuro Ilppliclltion. Z Green sweclclo\,er, drY'lIIl1ller conlent oqunl to iow rute of IIIlInure IIPpliclltion. ~

Ul >-3.... C:l

~ o Z Ul

tt

http:toIlI121.12http:101111211.88

44 'l'ECHNICAL BULLE1'IN 558, U. S. DEPT. OF AGRICUUl'URE

TAIlLB 15.-Comparison.~ and significance of run-off and erosiOll, experimellt 3, Aug. 31, 1.932 to Dec. 31, 1.985

Series 'Plot HUII.off Plot DltTer'l S' 't! 110. 'J'rcatnwnL 'rrentulcnt.- Hunon enloe per Igill 110. ncrc 1 cnll(~e 2

I----------------I----------.---~--

Inc/If.' IlIrlle.,a rePll sweet clover 4.2.1 2 Orcell sweetciover I/IIChl'";,. 2H -1.01 "Xcgutivc.(hi~h,., (low) . do... :l 16 tOllS Illll II lire pcr llcre :I. 1:1 +.S2 Do. " !!5II do. .1. 25 1 "tons JIIUIJ1Ire pcr nere. f ~;~a2 -2.0i 1'os{tivo.

I' u {_all. 2.; Do.(highJ.l (10\\").'tl do I~'(J.(H S 10 tons monure pcr nCft'. 11:1. !HI +6.0.; NegllIi vc,

I~'O. O-l !l R tons nulOurc t)~r ncn,l 115.80 -2.i.B~ Posill\c.81 :IL ....... 120.(14 III ('heck 1!1O.i:I -in. on High.7/ Onl(.lf} swectcJover 150.2\1 S 1(i tons mUlJuro per acre lIa. 1~1 +:10.:10 Do.(low).4 FIII111W 7' do Im.~'\l 0 S fons JIlut1urc per Jlcr(l'" H.i.Rfl +1.-1:1 Ne~llti\c.7 do ~ ~_ )[0(). 211 10 Cheek.. 1110.73 -40.-1-1 IIigh.

S , 10 (OilS 1llHnUrn fler 11:1. \X) !I S tons lIIJll1tJro JJer acre 115.80 -31.8i Do.1 nrre. .do................ II:I.!nJ IV Check.................. 100. i:l ,-70,7.1 Do. s tOilS IIlnnu~o per H5.S!l 10 .do................ Do.

I 11)0. 7:1 i-"' S7 iHerl'. j

DilTcrellcn ohtllilllxl ill ~lIrh inslllnce by suIJlrncLIlIg lhn tI~urcs in cohlllU1 71rolll those in colullln .1. , [ndh'idIl111 records Il~Ccl lor 1I11111ysis 01 \'lIrill Dt'll to dctermine significlIIH'e "I differences between 1)1015. 3 OreOll swec(clf)\er. cln"llIlItter c(lnlent equllito thllt. 0110 tons manure per lIern trelltment. Green sweet"lo\'e.. , d6"IIII1Lter conten~ eqlllil to that of 8 (ons mllnnrc per Il('ro (rcHLment.

I

45 SOIL AND WATER CONSERVA'l'ION I~VESTIGATIONS

As pointed out previousiy i.n conneotion with vegetutive cover, simill1T effects nre found in the experiments generally. Throughout all of the data the trend townrd reduction in run-off with vegetl1tive cover is I1ppnrent and accompnuying this reduction in run-off there is a fnr greater reduction in total erosion. In the same woy treatments which cause stimulation of plant growth increase the protection of the soil both ItS to run-off nnd soil losses, but the protection ngainst soil loss is proportionally grenter.

SEASONAL OCCURRENCE O~ nUN-O.,.]" ANI> EHOSION

The seasonnl occurrence of run-off from these tl'elttments is shown in figure 25. Here the far grenter losses from the fallow series than from the corn series nre illunediatel)r nppilrent. l:osses occurred throughout the months of. 1vlarch to November, mclusive. The figure shows thnt the check plot produced reln.tively more run-oft during Juno, ,July, August, September, ttll(l October-that is to sny, the mnnure applications glwe ell'ective control during this period. On the other hn.nd in November and the following ApI'il other troll.tn.ents yielded more run-off thnn the check plot, nnd this mny be tnken to indicate thnt the effects of the treatment were at len,st partially lost followinf; the sumJller period of high tempemtures. There were indicntions 1Il the study from time to time tlmt the green-mnnure treatments had lost their effectiveness comparatively early, owing pl'obnbly to more rapid decomposition thltll is the case with the JIlanure treatments. For this reason fl, sepnrn.te study has been outlined in eoopern.tion with the I\gronomy department of the IowaStateCollege, having for its purpose the determination of the factors which affect the mte of decomposition of these two forms of organic matter, and their subsequent effect on soil stl'llcture.

In the tLbove figme the Tun-ofi' from the corn series, plots 1-5, is also shown for the vnrious months of the yelLr. One item of interest lies in the difrerenee in run-off tlutt occulTed in 1{aTch and April and which may be attributed only to the presell

46 'l'ECHNlCAL DULLE'l'lN 558, U. S. DEPT. OF AGRICUL'l'URE

4

3

-.... 2

rFroM LcFT TO QIGHTo PLOT" 6.7.8.9;'10. ~ I FALLOW SEQIe.::;

~ ii! g ~ -~f,,=,~,--~.~,~~

~ (:i I

~ Q:

2

rOOM LeFT TO 12IGHT PLOTS 12.3.4 5. eOQN SERIES.

}~IGl'HE 25.~OrgnlJic mutter nud St)i1 renewal, :;casonnl (lCcurrellce or run-olf, experiment :-1, Hlaa-!t*i,

47 SOIl, AND W A'fER CONSERVA'J'ION INVESTIGA'l'IONS

10

1'120H Lt!f'r n:> Q/~l1r PLOTS 6. 7. 8. 9 1.10 FALLOW 5t::t:>Ie:S

30

10

rlXJM LerT ro qUIrtT PLOTS ~ 2. 3. 4, 5 COQN 5l!Q'~S

NOV. Qt:II;

.It"'lOultl-~""~*-Orgnl1ic nlatter JlIHl $011 rcuoW1l1, seasollul (lccurrClIt'c- or crosicm. c~pcriIl}Cnt, ;i, lUa:t-:-Js.

48 TECHNICAL BULLETIN 558, U. S. DEPT. OF AGRICULTURE

T'\BL~} 16.-Suil-lIloi8illn! deter1llinations on fallow pl(/t.~, experiment 8, Sept. 24, .1985

--.~ .. ~--.--------------:;olllJlo!slUrc ilL dfITcrcnL depths

Plot und trentlllent

PercedI Percenl Percent Percent Percent u.dghltu6 green sweetclo\'er high 1_.... 20.3U !.!S.2l 24.00 25.07 25.287 green sweetclo\'or low'.................. ! 26.11 2.1.35 24.49 2:1.30 24..iL'''18 16 tOllS lJIanuro pcr nere............... :!S.38 27.01 23.114 2:1.00 25.039 8 tons ntn.nure per Ilere .. ~ .... ~ '" ~ .. '.Ii. t L< _.. 26.59 2:1.35 21.05 Zi. ;5IOcheck... ,. . _... ._- -' .- "1 2.i.~~j 2.1. 'i:l 22.10 !!2.00 23.211

I Green sweetelo\'cr applicntion, dry mlltter cqllnls thllt of 10 tons IJIllnurc per acre. t Grccn sweetcio\'cr IlJlpllcntion, dry IJIlltter eqllnls thnt of Ii tons 1JI1inUreller nere.

I HIGH -e,1

] i

J I 1 ~

In gcncrlll the moistllJ'c- content of the plot rcceiying the low rate of manlll'e is interllledinte between the moisture ('.ontent of the check and that plot rccciying the high rnte of mllnure. In a general way also, the moisture content of the plots receiving grcen-maIlure treatment is similur to tha.t of the plots receiving stnble manure. Thus the chcck plot with its lIlt'ger l'un-off does, in fuet, show the eft'ects of this greuter loss in its lower aycrage contcnt of soil moisture.

MEAN HEIGHTS OF COHN PLANTS GHOWN

Tbe rate of growth of COl'll on these various plots is determined regularly in the same manner us in experimcnt 1. Euch plant is measlJ)'cd upon a centimeter scule 11 t lO-day interYllls from an early stnge of growth until fullhcigbt is n.ttained. The melln plunt heights for the yeurs 1933-35 arc shown in figure 27, It is secn thu t in each

SOIL AND WATER CONSERVATION INVES,]'IGATIONS 49

one of the years plots 3 nnd 4, treated wit.h manure, produced the greatest growth. 'The check treatment, plot 5, usually produced the least growth. 'l'he effects of the high temperntures nnd the low rainfnll of the 1934 drought yenr nre seen in the growth curves in two ways: (1) The totnl growth for the season is only 190 em., nnd (2) the rate of growth of the mnnul'ed treutments fell oft' markedly after July 19. This dute corresponds to the beginning of a period when temperatures exceeded 100 li'. for a succession of days, and reached as high tlS 114.

CROP YIELDS

An examination of the data giving the crop yields from this experiment (table 17) shows marked response to the organic-matter additions which hlLve been made, On the corn series in 1933 from 75 to 90 bushels an acre of com were secured from the better tl'eatments, an illcrense a,hove the check plot of more than 200 percent. In the drought yenr of 1934 the mnnure treatments decrensed yields (as did clover in the Totntion series of experiment 1)J but the green manure nearly doubled the yields. Agllin in 1935 the yields of all treatments were distinctly superior to those of the check plot. Yields for the corn series were not tnken in 1932 because of the disturbance of the plots during installation of measuring equipment-1933 was the first crop yenr for the rotation series. A comparison of the yields from the COl'll series with those of the rotution in 1933 shows the recovery from the desurfacing opemtion when the check plots alone aTe considered and the benefit derived from two applications of barnyard manure us compared with one,

TARLE li.-('rop yields 1 from experiment. ,'j

1034

PIOl TrentmenLno" Ornln TIny or 0' I lIllY or Ornin Ilnyorst O\'cr r.1 11 sto\'cr SlO\'er

per Here per llcrc '% per nero per ucre per nere per acre

--1--------------1----------------- BIt.,h,!., Ton" Bushel., Ton. l1u.hrl., 'j'01l8

1 Corn+green sweet~lo\'er, high rate 3. _., 90.114 16.32 1. :19 :19.59 2.11 2 C'orn+grccn swcetc1nver t low rate 4~ _ .. _~ 84.11 17. SIl 1. ~'9 25.31 2.10 :1 ('orntl6 tons nlllnure per lIerc__ . __ __ is. OS 5.11 U6 26.91 2.07 4 Corn S tons nlnnuro per ncre__ .. ~ ...... ,",,,_~ 5.1. i5 4.93 1.19 30.~ 1. i3 5 ('om check.... _. , .. _............ 33.37 0.36 .7:1 21.tl3 I. 56

11 Hot.lIl1an '+green swcetelo\'er, highrate 3 ._ ................ __ . _.. _ 4I.a4 13,07 5'> (2l ,67

12 Uatlltion '+grecn sweetcloyer, low rate 4 .. _ ...... _ .......... m ... ,.~ .. "'.~ ............. _ .... 42. 72 9.34 .36 (I) 3"

13 RQtlltlon '+10 tons manure per IIcre __ ~1.!l7 0.57 .40 (2l .9t 14 Hotlltion '+8 lons manure per lIero._ 18.91 0,89 .33 I No crop hnrYcsted or yield not determined. , Green sweetclonr, dry matter eqlllli to thllt of nn nppifcntion of.l6 tons nll1nure per IIcre Green swcetcloycr, dry mntter e'lunl to thlll of lin IIppliclllion of S t

50 'J$CHNICAL BULLE'l'IN 558, U. S. DEPT. OF AGRICULTURE

difficulty in obtaining germination of clover seed during the preceding veal', the increase in clover hay was aJ?preciable. Dates of crop planting and harvest are given in the detailed log of treatments (tables 81 and 82).

Trends of this character are to be expected. The points of interest scem to lie particularly in the magnitude and consistency of the effects of conserving soillmel wnter, fiS well as the simultaneous effects upon crop Pl'oeluction-nll achieved economically and along the lines of conserYatiye treatment.

E...:C'l' 0.' LI~NG'I'H 0.' SLOI'}: ANI> nIREC1'ION OF ROW, EXPERIMENT 4

I,ENOTH OF SLOPE

It has bceome inel'casingly apparent tlu\,t the relative run-off thn t ON'UI'S fro1l1 slo pes of difTcren t lcn~ths is directly related to the fnctors of l'I1i.nfnll intensity llnd infiltm.tlOn rnk

EROSION -TONS PER ACRE, 16 t 0 RUN'OFF-PERCENT OF TOTAL PRECIPITATION, ~ t~

~..

11

I I. ~ n ., n o '" VI ~l-z ~ g0... S !) ~ u"

o~" ,,f ~j.,.,"'a: ~~ I- .~~.~! t ~~

jo'Wl'ln; 2S.-" Soli tllld WilIer losses A t1g. 15, \032, to Dec, aI, 1fi35. 'I'otul precipitation 00.011 inches; etfectlve IJrccIpItllUon :Ji.IH Inches; experiment 1, Mnrshtlll slll.loum; average slope, S percent.

In the compnrison of length of slope in cxpclimcnt 1, there was some doubt ns to whethe!' sufficient differences in length had been provided in tho original plnns, If relative run-off is determined by the relntionship of infiltrntion rate tominfall intensity, then it is obvious thn.t it propel' comparison of slope length must contnin such differences in the compnTison as to ullow appreciable time for infiltration to occur on the yaIious lcngths under study.

SU~[I\IAnY 01' RUN-on' AND EROSION DATA

These considerations gave rise to the present experiment in which ycry muC'h wider differences in slope length hnve been included. The results scc-Ul"ed during the period of operation of this exyeriment from August 1932 nre presented in table 18. Individua run-off and erosion records are given in tables 86 and 87. The differences in run-off and crosion due to slope length are shown graphically in figure 28. It is seen that the total erosion on the long, medium, and

51 SOIL AND WA'J'ER. CONSEHVA'l'ION INVES'J'IGA'PIONS

short length of slope WitS Itbout 67, 53, find 40 tons per u'el'c, respe{'~ tively. The run-off from these slopes totaled more than 5, 7, nnd !J surface inches, respectively. Thus, ns the length of slope incrensed, the total erosion increased, but the total run-off decreased. Taking fiS It premise the belief expressed above thn,t rela,tion of rainfall intensity to infiltration rnte is a determining factor, one is led to the thought that these rcintive differences may reverse themselves in direetion when rainfall characteristics Vttry from stonn period to storm period. An examination of the datn. shows that the trend hns reYerse(l itself for different rains as has been pointed out previously (10).

TAllLE IS.-Sum1/lary of runoJ! anri cro.~ion I fro/l1. 7J/O/S 1-4, experiment -1, A 11(/. 15,1982/0 Dec. 81,1085 .

rA yernge slope, 8 nercen t] .--.... '". ...-. ... -4\1J~. 15 2-Dcc, 31, HI~a 3 I1i:H

l!1~2

:: :: ,,.~ RunotT Ttun-olT Itun-oll c 'l'renlrnonl ;:'" '" ::;:".. ~ ~ c ., '" 0::. .. '" 0::. ., a

c c b ~ ~ .." bO " "0 iii .~ " E ,~" 'iii ,~ c a a B a;;: ...:I " '" -:: A " " ~ -:: A" ~ -:: A " " ~

-_.\----------.\------------------Fcct In", Lb", 7'ons In", Lb", T01ls IIl,fl. Lb", '1'011,'(laO Rows with slopo............. U,g\ 1. 8:1 2.78 2.54 i,1Il :H.IH 0,(1\ J.n!) 1. 20 815 do............. __ ......._. .72 2.115 3.84 2.1;.1 4.35 20.U7 1.00 .38 no____________ ..a lIii'02 .....do...______ 1. 2.1 2.02 4.57 3