WINTER PR.ECIPITATIONI

Transcription

1 CONSE,RVATION OF SOIL MOISTUR.E FROM FALL AND WINTER PR.ECIPITATIONI W. J. Srri-o, J. J. Lnne,lrn enn A. WBxuenr2 Cond Deprtment oj Agriculture, Swift Current, Sshtchewn [Received for publiction June 7, 959] ABSTRACT Twenty yers' results shou'ed tht 37 per cent of the over-lvinter precipittion t Swift Current ws conserved in stubbie fields nd 9 per cent in fllo',v. Further nlysis showed tht rinfll nd snorvfil were conserved eqully rve in stubble but tht conservtion in fllolv rvs rnostly from rinfll. Much of the snow ws blown from the fllow nd ccumulted in the stubble. Fli moisture rvs lso fctor, in tht ech inch of moisture stored in the soil in the f[ reduced the over-winter conservtiou by pproximtely 0.2 inch. Nine yers' results rvith fll cultivtion on stubble showec tht one-wy diskilg fter hn'est reduced the winter storge in 3 yers out of 9. Apprently ny gin in moisture conservtion from the removl of v"'eed growth 'ws more thn offset by reduced snow ccumultion during the rvinter. Blde tillge in the fll resulted in greter moisture storge t seed-time in yer out of 9. INTRODUCTION Erlier work t Swift Current showed tht bout one-third of the precipittion received on stubble lnd in the fll nd winter ws conserved for the succeeding crop. Conservtion in bre fllow over-winter ws rnuch less thn this becuse of snow blo.ving nd spring run-off. In the present pper, 20 yers' results re nlysed to show the seprte contributions mde to moisture storge by rinfll nd snowfll receil'ed during the lte fll nd 'r'vinter. The influences o{ fll moisture nd of different types of fll cultivtion re lso ssessed. REVIEW OF LITERATUR,E The mount of soil moisture stored from winter precipittion is highly vrible becuse of losses from evportion, snow blowing nd run-off. Brnes nd Hopkins () on the bsis of 7 yers' experiments with crops grown in tnks t Swift Current, Ssktchewn, found no pprecible increse in soil moisture from snow cover. In lter report Brnes (2) pointed out tht the run-off from frozen soil ws not ll lost, s it ccumulted in low plces nd the wter ws bsorbed fter the soil thwed out. A report by Stpte nd Lehne (0), bsed on field smpling on Illustrtion Sttions in southrvestern Ssktcheu'n, sho'i'i'ed tht 'r'r''inter precipittion, mostly snowfll, ws consistently beneficil in stubble but ws frequently negligible in fllow. A men of 33 per cent of the winter precipittion ws stored in stubble nd only 6 per cent in fllor,v. Subsequent work on field shelterbelts by the srne uthors (2) showed tht the min gin in whet yield ner tree ronrs \vs due to snow ccumultion. Mtthews (6) t the Scott Experimentl Frm found tht snow ploughing in fields to prevent drifting incresed soil moisture in the spring from 0 to 30 per cent. ---6lit.ibution from the Experimentl Frm, Swift Current, Ssk' 2Physicist, Soil Physicist nd Agronomist, respectively. 80

2 Februry, 960] sraple ET AL.--toNsERvATroN of sorr- MorsruRE 8 Thysell (3) t Mndn, North Dkot, showed tht three times s much moisture ws conserved from hrvest to seed-time in stubble s in fllow lnd. Initil soil moisture content, s well s snow drifting, ws n importnt fctor; more moisture ws conserved in bre, fll-ploughed stubble thn in fllow. \tlthews (5), in review of moisture storge nd its use by spring whet in the Gret Plins, found tht cultivtion fter hrvest incresed moisture storge in the southern res, but tht plots without fll tillge conserved more moisture in the north. These results were ccounted for by differences in snowfll nd in weed growth in the two climtic zones. Power et l. (7) in northestern \llontn G99-56) found tht neither fll blding in stubble nor fll chiseling in fllow incresed soil moisture or crop yield. Observtions indicted tht subsurfce tillge in stubble fter hrvest might be useful {or weed control under some climtic conditions. Results from fll tillge in southrvestern Ssktchewn (8) depended on the r,vether experienced during the fll nd winter. OVER.WINTER CONSERVATION IN STUBBLE AND FALLOW Method. Moisture conservtion in {llow nd stubble for the period ws determined by soil moisture smpling to depth of 4 feet in field plots fter hrvest nd gin t seed-time. The smpling ws ssocited with culturl experiments so tht the ctul size of plot nd dte of smpling differed somewht from yer to yer nd between fllow nd stubble. Sixteen to tr'venty sites were smpled most yers, four sites being chosen on ech of four or five plots. Ferver smples rvere tken during the wr yers when some of the smpling hd to be omitted. Sub-smples were tken in depths 0-6, 6-2, l2-2+,24-36, nd inches. Soil moisture contents in per cent by weight r''n'ere determined by the grvimetric method. Fll nd spring smples were tken within few feet of ech other, nd the moisture storge determined by subtrction. Avilble fll moisture ws obtined by substrcting the wilting percentge from the totl moisture content t fll smpling. Wilting percentges were determined prtly by the direct method using sunflowers (4) nd prtly by the desicctor method (4). Rinfll ws mesured with the Cndin stndrd rin guge (re 0 squre inches). Snowfll ws estimted by mesuring the depth of fresh snor'v in sheltered sites nd multiplying by the men wter equivlent, 0. inch of wter to inch of snow. These observtions were mde t the Experimentl Frm, distnce of pproximtely 2 miles from the field plots. Until recently it ws not fesible to obtin records over-u'inter nerer the plot re. Results Soil moisture nd precipittion dt re given in Tble. N4oisture conservtion in columns 5 nd 9 show high vribility. This ws relted to the mount of rinfll nd snowfll received, but mny conditions of soil nd wether lso contributed to the result. The rinfll ws greter for stubble thn for fllow becuse stubble fields were sometimes smpled

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4 Februry, 960] sraple ET AL.--{oNSERvArroN of soil MorsruRE 83 erlier in the seson. In few cses snowfll received in October nd April ws included with the rinfll becuse the ground ws unfrozen nd the snow melted rpidly. Negtive vlues for fll moisture in stubble (column 2) were due prtly to the surfce soil being below the wilting percentge when smpled. In some yers, too, the subsoil fter hrvest my hve been dried slightly below the lbortory-determined wilting point. Negtive vlues for moisture conserved in fllow (column 9) usully men tht no wter ws dded to the subsoil over-winter. nd the surfce ws drier t seed-time thn t hrvest. The men moisture conservtion in stubble ws 2.0 inches nd in fllow 0.43 inch. This ws 37 per cent of the over-winter precipittion in stubble nd 9 per cent in fllow. The men vilble fll moisture in stubble ws.30 inches nd in fllow 3.99 inches. From these figures one might expect negtive correltion between fll moisture nd conservtion. Such reltionship undoubtedly exists becuse evportion nd run-off losses increse with soil moisture content, prticulrly when the subsoil is f.rozen. However, s will be shown lter, much of the difference in moisture conservtion ws due to snow blowing off the fllow nd ccumulting in the stubble. The moisture conserved over-winter plus the fll storge give totl of 3.3 inches vilble moisture in stubble nd 4.42 inches in fllow t seed-time. These vlues re slightly higher thn those obtined by Stple nd Lehne () for the longer period Dt in the present pper re high, prtly becuse of bove verge precipittion during the yers In ssessing the reltionship between conservtion nd precipittion, the liner regression ws {irst worked out for both stubble nd fllow. These equtions re given below where C represents over-winter conservtion nd P the corresponding precipittion, both in inches of wter: stubblec:0.35p+0.08 Fllow C:0.20P-0.55 () Anlysis of vrince in Tble 2 shows tht the regression for stubble ws significnt t the per cer-rt level nd tht for fllow significnt t the 5 per cent level. The fiducil limits (p : 0.05) of the regression coefficient were 0.3 to 0.57 for stubble nd 0.04 to 0.36 for fllow. The correltion coefficient for stubble ws 0.65 nd for fllow 0.5. In other words, 36 per cent of the vribility in conservtion ws ccounted for by the liner regression in stubble nd 25 per cent in fllow. The tendency towrd higher regression coefficients for stubble compred with those for fllow must be due in prt to snow ccumulting in stubble nd blowing off fllow. Since this effect should not be pplicble to the rinfll, it seemed worthwhile to seprte precipittion P into its two components. Regression equtions including vribles S for snowfll nd R for rinfll re given below: stubble c : 0.38 s R Fllow C: R-0.5 Q)

5 CANADIAN JOURNAL OF SOIL SCIENCE [Vol. 40 Tble 2 shows tht seprting S nd R reduced the error vrince significntly on fllow but hd little effect on stubble. The regression coefficients for snowfll nd rinfil were significnt nd nerly equl on stubble, wheres the coefficierrt for snorvfll on fllorv lvs fr short of significnce nd tht for rinfll ws signihcnt t the per cent level. The n-rultiple correltion coefficient ws now 0.66 for stubble nd for fllow. Aprt from effects due to snow blowing, the conservtion of snowfll is influenced by fll moisture nd depth of {rost. A wet lrozen soil is reltively impermeble to wter, nd, when rpid thws occur, losses re high from both run-off nd evportion. Stubble fields re less susceptible to such loss thn fllow becuse they re usully drier in the fll nd the snow cover reduces frost penetrtion. Avilble moisture in the soil in the fll, F, ws included s fctor in the regression equtions to give: stubble c : 0.4 s R F Fllow C : 0.04S +0.50R - 0.6F+0.30 (3) The dditionl fctor gin reduced the residul vrince for both types of surfce. \llultiple correltion coefficients were 0.7 nd for stubble nd fllow respectively. The regression coefficient for fll moisture on fllo.,v r'vs significnt t the 5 per cent level wheres tht on stubble ws just short of significnce. The fiducil limits (p : 0.05) of these coeflicients were for fllorv to , nd for stubble to Little difference would be expected between the coef;ficients on the bsis of the fctors involved. The men reduction in conservtion due to indirect effects of fll moisture would be bout 0.3 inch in stubble nd 0.6 inch in fllow. The higher regression coeflicient for rinfll on fllow reltive to tht on stubble is not redily explined. The hducil limits of 0.30 to 0. 7 for fllow nd 0.0 to 0.63 for stubble indicte tht the difference is not significnt. Some dditionl benefit from rinfll on fllow might be expected in the erly spring when the fllow surfce is dry but the stubble is still u'et from the sdrins thw. Teern2'-AN"'"""iJi:'i,Iu";?;"T;I'ffi iiconservarronrnfal'low Vrince ttributble to Liner regression with Prec. Residul Additionl effect, seprti PintoS&R Residul Additionl effect, dding F S&R Residul DF o.7 r ** O9 DF *Significnt t 5 per cent level ++Significnt t Der cent level

6 Februry, 960] sraple ET AL.-coNsERvATroN of sorr, MorsruRE 65 The residul vrince shows tht 49 per cent of the vribility remined unccounted for on stubble nd 36 per cent on fllow. The conservtion, C, bsed on soil smpling would involve firly high experimentl error. Errors in mesurement of rinfll nd snorvfll would be smll compred with the moisture losses involved. Improvement in the mesurement of F would not help much; this fctor ws included becuse of its indirect influence on evportion nd run-off. Fctors not tken into ccount specificlly include: ) evportion from bre soil in fll nd spring, nd from snow during the winter; 2) run-off, which my vry from yer to yer depending on the nture of winter nd spring thws; nd 3) percoltion beyond the root zor-re. Without these losses, of course, the coefficients for S nd R would be ner unity nd tht for F r'vould be zero. NtIore informtion is needed before the dispenstion of winter precipittion cn be properly ssessed. Evportion from bre fllow during the summer months t Swift Current ws studied by Hopkins (3) nd by Stple nd Lehne (9). Presumbly evportion losses in fll nd spring, when the soil is unfrozefl, cfl be predicted by n extension of this erlier work. Further dt re needed on evportion from snor,v nd the meteorologicl fctors producing spring run-off. The correltion between moisture conservtion nd men ir temperture over-winter is very low; temperture s n dditionl vrible in the regression eqution did not reduce the residul vrince pprecibly in either stubble or fllow. Losses from deep percoltion re not usully problem under semirid conditions. The men conservtion in summerfliow by seed-time (Tble l) is 4.42 inches of wter, wheres medium lom soils will hold 6.5 inches in the 4-foot root zc:ne. However, some loss usully occurs due to slow cpillry movement rvhen moisture exceeds 5.5 inches. Vrying mounts of moisture rvere lost by percoltion in fllow follor'r'ing June rins during the period 95 to 956. Even in stubble in erly spring, some moisture pssed below the root zone in ycrs such s 95, 952, 953 nd 955. 'fhe losses were exceptionl, nd the mount of r'vter involved $/s probbly smll. Usully good mesure of moisture infiltrtion nd storge cn be obtined by smpling to depth of 4 feet in ciys nd medium loms, nd to 5 feet in fine sndy lom. FALL TILLAGE AND CONSER.VATION Fll tillge of summerfllow using dmming listers ws tested in the lte 30's, with the object of holding snow nd trpping spring run-off. Tests conducted t 0 sttions in southwestern Ssktcheu'n* for 2 yers, 938 nd 939, showed no significnt gins in moisture in listed fields t seed-time. The dt nd field observtions did not give much promise of incresed over-winter conservtion in fllow through specil tillge. Experiments described here were designed to find the influence of fli cultivtion in stubble fields. Gins in soil moisture conservtion might result from reduced weed growth nd greter moisture penetrtion. EipuWirnrA dtu. Anrulreports, Soil Reserch Lbortory, Swift Current, Ssk,

7 86 CANADIAN JOURNAL OF SOIL SCIENCE lvol. 40 Method, One-wy disking nd blde-type tillge on stubble fter hrvest were compred with n uncultivted check for the 9-yer period, inclusive. Moisture conservtion ws determined s described previously, tking soil smples fter hrvest nd gin t seed-time. The fll cultivtions rvere prt of lrge experiment contining eight tretments qudruplicted in rndomized block design. One wekness of the lyout ws tht the one-wy disked nd blded plots were plced side by side, rndomized with respect to north nd south position, nd included s pired plot in the rndomiztion of ech block. Snow blowing from the onewyed plot could lodge in the blded plot nd enhnce the moisture there. This must be kept in mind in ssessing the results. The plots were ech 80 feet wide by 600 feet long, comprising pproximtely. cres. Four soil smples for moisture determintion were tken in ech plot so tht, with four replictes, sixteen smples were vilble from ech of the three tretments. Smples were tken s usul to depth of 4 feet except in dry yers, when depth of 3 feet ws sufficient. Fll nd spring smples were tken within few feet of ech other to minimize vritions due to differences in soil texture nd run-off. Results Results of soil moisture smpling for the 9-yer period re given in Tble 3. Precipittion includes both rinfll nd snowfll occurring between the smpling dtes. The 35-yer verge snorvfll in the re is bout 35 inches or the equivlent of 3.5 inches of wter. The verge snowfll for the 9 yers shown in Tble 3 ws 45 inches, considerbly bove the verge. The dt given for the three tretments in columns 3, 4 nd 5 re verges of 6 determintions t lvj4-j s yer v. Tet-r 3.-E!'FEcr of FALL cultrvation on MoISTURE srorage n Moisture conserved, fll to spring One-wy disk I I.88 Blde ln J)< )LQ No fll cultivtion n L.tl? cc T.2L J"/o -. ln I.05 N,S s5 Lest significnt difference % N,S. 0.74

8 Februry, 960] sraple ET AL,-coNSERvATroN of sorr. MorsruRE 87 Vribility between individul smples ws high becuse of uneven snow distribution, nd run-off into low plces in erly spring. In extreme cses the depth of wter penetrtion t seed-time vried from 2 feet to over 4 feet. Tble 3 shows tht L.S.D.'s of the order of 0.6 inch were required for significnce between tretments. Snow blorving on to the experimentl re from djcent flloi,v lso cused differences betrveen blocks, or produced interctions between blocks nd tretments. Despite these difficulties, it is believed tht the reltively lrge plots used in the experiment gve better mesure of lrge-scle phenomen such s snow distribution thn r'vould be possible in smll plots. Border strips between blocks of fllow nd stubble r,vould reduce vritions due to snow blowing. The results show tht moisture conservtion in the one-wy disked plot ws significntly lou.er thn in the check in 3 yers out of 9, viz., in 950, 953 nd 957. The moisture conserved in the blded strip ws significntly higher thn tht in the check in one yer, 95, nd it ws bout inch higher thn in the check, lthough not reching the 5 per cent level, nother yer, 956. The error of the experiment.lvs prticulrly high in 956 becuse of interction betrveen blocks nd tretments. In the other 4 yers the differences between tretments were fr short of significnce. It rvill be noted tht losses with one-wy disking did not occur in the yers tht gins were obtined r,vith blde tillge. The loction of the blded plot djcent to the one-wy disked plot ws mentioned erlier. This might fvour the blding, but when the ltter showed definite dvntge in only yer in 9, the result is not likely to misled. Also, on Mrch 22, 95I, the depth of snow ws 5 to 24 inches on stubble lnd nd 7 to 5 inches on fllow. With ll stubble completely buried it seems unlikely tht the blded plot rvs much influenced by dditionl snow blorvn from the djcent plot. In other winters, with less sno\v or with recurring th.lvs, the sitution might be different. Discussion Mny soil nd wether conditions re involved in moisture conservtion over winter. The 9 yers' dt indictes tht fll cultivtion of stubble fields should not be recommended in the Swift Current re. Further exmintion of the dt might help, horvever, in extending the results to climtic zones rvhere the fll nd winter conditions re similr to those experienced t Swift Current during specific yers of the test. It is doubtful if weed control by fll cultivtion incresed moisture conservtion pprecibly. Weed infesttion ws not severe; the soil ws often dry fter hrvest nd moisture use low. Fll weed growth ws presumbly less importnt thn t Lethbridge, Albert, where gins in crop yield from fll cultivtion over I2-yer period were ttributed lrgely to the destruction of lte-mturing nnul weeds before they set seed*. The present discussion pplies only to moisture conservtion in the current fll nd winter period, nd not to fll tillge s weed control mesure. In generl, the dt nd observtions in Cnd re in greement with those of Power et l. (7) in N4ontn. The influence of fll tillge on weed infesttion should be considered further t some loctions. *Priute conesbondence, G. C, Russell, Hed, Soils Section, Experimentl Frm, Lethbridge, Alt.

9 88 CANADIAN JOURNAL OF SOIL SCIENCE lvol.40 Ftl blding produced significnt increse in conservtion in the spring of 95 under conditions of very high snowfll, little winter thw nd negligible moisture storge in the fll. Conditions were somewht similr in the ner-significnt yer, 956, with modertely high snowfll nd little thwing, but with.89 inches of vilble moisture in the fll. The yers 950, 953 nd 957, in which one-wy disked fields conserved less moisture thn the check, hd bove verge snowfll (43 to 49 inches), moderte mount of 'lvinter thrving nd low to medium fll conservtion. Reduced moisture in the disked plots resulted from less snow ccumultion where the stubble ws turned down. It seems possible, too, tht the thwing periods were sufficient to settle the snow in the stubble, thus permitting more to be trpped with successive storms, but not severe enough to cuse excessive evportion or seling of the soil surfce. In yers 952 nd 955, the former with high snowfll nd the ltter ner verge, effects of tiilge were possibly ersed by very high fll moisture contents. The other two yers, 954 nd 958, hd low to verge snowfll nd they lvere "open winters" with frequent thws. In the fll moisture ws lor'v nd pprently much of the conservtion cme from erly winter th'lvs. Lter in the seson run-off nd erosion were high for the mount of snowfll received. REFERENCBS. Brnes, S., nd E. S. Hopkins. Soil moisture nd crop production. Cn. Dept. Agr. 8u Brnes, S. Soil moisture nd crop production under drylnd conditions in Western Cnd. Cn. Dept. Agr. Publ Hopkins, - J. W. Agriculturl meteorologl': A sttisiicl study of conservtion of precipittion by summerfllou.ed soil tnks t Swift Current, Ssktchewn. Cn. J. Reserch, C, 8: I Lehne, J. J., nd W. J. Stple. Desicctor method for determining pertnnent wilting ncrcentses of soils. Soil Sci. 72i Mtheu's, O. R. Storge of wter in soil nd its utiliztion by spring rvhet. U.S.D.A. Dept. Bull Mttheu's, G. D. Snow utiliztion in pririe griculture. Cn. Dept. Agr. Publ L Porver, J. F., T. S. Asheim, nd G. P. Hrtmn. Spring production nd soil nd wter conservtion s influenced by methods of "vhet summerfllorving on Chestnut soil in northestern N'Iontn. Soil Sci. Soc. Amer. Proc' 22: Soil Reserch Lbottory Progress Report Cn. Dept. Agr Stple, W. J., nd J. J. Lehne. Estimtion of soil moisture conservtion from meteorologicl dt. Soil Sci. 58: Stple, W. J., nd J. J. Lehne. The conservtion of soil moisture in southern Ssktchervn. Sci. Agr. 32:36-47, L952.. Stple, W. J., nd J. J. Lehne. Wether conditions influencing rvhet yields in tnks nd field plots. Cn. J. Agr. Sci. 34: Stple, W. J., nd J. J. Lehne. 'lhe influence of field shelterbelts on wind velocity, evportion, soil moisture nd crop yield. Cn. J. Agr. Sci. 35: Thysell, J. C. Conservtion nd use of soil moisture t Mndn, N. Dkot. U.S.D.A. Tech. Bull Work, R. A., nd M. R. Lervis. N'Ioisture equivlent, field cpcity, nd permnent wilting percentge nd their rtio in hevy soils. Agr. Eng. 5: