chemical and stubble-mulch fallow influences on seasonal soil water contents1

6
Chemical and Stubble-Mulch Fallow Influences on Seasonal Soil Water Contents 1 D. L. TANAKA 2 ABSTRACT A study was conducted in the northern Great Plains to determine the effect of chemical and stubble-mulch fallow of a Williams loam (fine-loamy mixed, Typic Argiborolls) on soil water contents during 14-ahd 21-month fallow periods. Soil water contents to a depth of 1.70 m were measured by use of the neutron-scatter technique for two 14-and three 21-month fallow periods. The amount of surface residue after harvest ranged from 0.6 to 3.6 Mg/ha during the study. Chemical fallow maintained more surface residue than stubble-mulch fallow, but no significant differences in soil water contents to 1.70- m soil depth occurred between the treatments. Gain in soil water occurred after harvest and over the first winter with soil water loss generally occurring during summer for 14- and 21-months of fallow. No gain in soil water contents occurred over the second winter when chemically fallowed for 21-months. Precipitation frequency and dis- tribution may be just as important as quantity and position of surface residue for chemical fallow to effectively store more soil water than stubbie-mulch fallow. Additional Index Words: spring wheat fallow, winter wheat fallow, residue, conservation tillage. Tanaka, D.L. 1985. Chemical and stubble-mulch fallow-influences on seasonal soil water contents. Soil Sci. Soc. Am. J. 49:728-733. W HEAT (Triticum aestivum L.) grain production in the semi-arid Great Plains is limited by low and variable precipitation amounts. Summer-fallow- ing is practiced to increase soil water contents, control weeds, make nutrients available, and to stabilize crop yields. However, summer-fallowing is very inefficient in storing summer precipitation due to soil water evaporation (Haas et al., 1974; Black et al., 1974). Res- idue on soil surfaces can reduce evaporation by de- creasing air movement immediately above the soil, changing albedo, and insulating the soil surface. Therefore, management of surface residue can be a major factor in minimizing evaporation and increas- ing soil water storage during fallow (Army et al., 1961; Greb et al., 1967; Smika and Wicks, 1968; Bond and Willis, 1969; Smika et al., 1969; Greb et al., 1970; Hammel et al., 1981). Surface residue can be conserved by reducing or eliminating mechanical tillage. Factors resulting in residue losses from stubble-mulch fallow include res- idue incorporation and positioning by tillage. Brown and Dickey (1970) found that residue losses occurred in the following order: buried > on-soil surface > above-soil surface. Chemical fallow, the use of her- bicides to control weeds during fallow, results in a greater portion of residue above the soil surface than stubble-mulch fallow and less decomposition of sur- face residue. Fenster and Peterson (1979) indicated that chemical fallow resulted in 20 to 25% losses while stubble-mulch fallow resulted in 55 to 75% losses of wheat surface residue during a 14-month fallow pe- riod. Since chemical fallow conserves a greater amount of residue than stubble-mulch fallow, soil water evap- 1 Contribution from the USDA, Agricultural Research Service, in cooperation with the Montana Agric. Exp. Stn., Journal Series no. 1520. Received 2 July 1984. Approved 14 Dec. 1984. 2 Soil Scientist, USDA-ARS, P. O. Box 1109, Sidney, MT 59270.

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Page 1: Chemical and Stubble-Mulch Fallow Influences on Seasonal Soil Water Contents1

Chemical and Stubble-Mulch Fallow Influences on Seasonal Soil Water Contents1

D. L. TANAKA2

ABSTRACTA study was conducted in the northern Great Plains to determine

the effect of chemical and stubble-mulch fallow of a Williams loam(fine-loamy mixed, Typic Argiborolls) on soil water contents during14-ahd 21-month fallow periods. Soil water contents to a depth of1.70 m were measured by use of the neutron-scatter technique fortwo 14-and three 21-month fallow periods. The amount of surfaceresidue after harvest ranged from 0.6 to 3.6 Mg/ha during the study.Chemical fallow maintained more surface residue than stubble-mulchfallow, but no significant differences in soil water contents to 1.70-m soil depth occurred between the treatments. Gain in soil wateroccurred after harvest and over the first winter with soil water lossgenerally occurring during summer for 14- and 21-months of fallow.No gain in soil water contents occurred over the second winter whenchemically fallowed for 21-months. Precipitation frequency and dis-tribution may be just as important as quantity and position of surfaceresidue for chemical fallow to effectively store more soil water thanstubbie-mulch fallow.

Additional Index Words: spring wheat fallow, winter wheat fallow,residue, conservation tillage.

Tanaka, D.L. 1985. Chemical and stubble-mulch fallow-influenceson seasonal soil water contents. Soil Sci. Soc. Am. J. 49:728-733.

WHEAT (Triticum aestivum L.) grain productionin the semi-arid Great Plains is limited by low

and variable precipitation amounts. Summer-fallow-ing is practiced to increase soil water contents, controlweeds, make nutrients available, and to stabilize cropyields. However, summer-fallowing is very inefficient

in storing summer precipitation due to soil waterevaporation (Haas et al., 1974; Black et al., 1974). Res-idue on soil surfaces can reduce evaporation by de-creasing air movement immediately above the soil,changing albedo, and insulating the soil surface.Therefore, management of surface residue can be amajor factor in minimizing evaporation and increas-ing soil water storage during fallow (Army et al., 1961;Greb et al., 1967; Smika and Wicks, 1968; Bond andWillis, 1969; Smika et al., 1969; Greb et al., 1970;Hammel et al., 1981).

Surface residue can be conserved by reducing oreliminating mechanical tillage. Factors resulting inresidue losses from stubble-mulch fallow include res-idue incorporation and positioning by tillage. Brownand Dickey (1970) found that residue losses occurredin the following order: buried > on-soil surface >above-soil surface. Chemical fallow, the use of her-bicides to control weeds during fallow, results in agreater portion of residue above the soil surface thanstubble-mulch fallow and less decomposition of sur-face residue. Fenster and Peterson (1979) indicatedthat chemical fallow resulted in 20 to 25% losses whilestubble-mulch fallow resulted in 55 to 75% losses ofwheat surface residue during a 14-month fallow pe-riod. Since chemical fallow conserves a greater amountof residue than stubble-mulch fallow, soil water evap-

1 Contribution from the USDA, Agricultural Research Service, incooperation with the Montana Agric. Exp. Stn., Journal Series no.1520. Received 2 July 1984. Approved 14 Dec. 1984.2 Soil Scientist, USDA-ARS, P. O. Box 1109, Sidney, MT 59270.

Page 2: Chemical and Stubble-Mulch Fallow Influences on Seasonal Soil Water Contents1

TANAKA: CHEMICAL AND STUBBLE-MULCH FALLOW INFLUENCES ON SOIL WATER 729

oration should be reduced and ultimately result ingreater soil water storage during fallow.

Tillage comparisons in the central Great Plains haveindicated that chemical fallow allowed more soil waterstorage than stubble-mulch fallow during a 14-monthfallow period (Good and Smika, 1978; Fenster andPeterson, 1979). Comparisons from the northern andsouthern Great Plains show little differences in soilwater storage between chemical and stubble-mulchfallow for either a 14- or 21-month fallow period (Wieseand Army, 1960; Army et al., 1961; Black and Power,1965; French and Riveland, 1980; Johnson and Davis,1980). These discrepancies along with limited residueinformation, lack of intensive soil water measure-ments, and little information about precipitation fre-quency and distribution make chemical and stubble-mulch fallow comparisons in the Great Plains difficultto interpret and make it almost impossible to deter-mine when soil water differences will occur during thefallow period. Therefore, the objectives of this re-search were to compare seasonal soil water contentsfor chemical and stubble-mulch fallow and monitorprecipitation and quantity of surface residue through-out winter and spring wheat fallow periods in thenorthern Great Plains.

MATERIAL AND METHODSThe study was initiated in April 1980 on a Williams loam

(fine-loamy mixed, Typic Argiborolls) 11 km northwest ofSidney, MT. The field had previously been seeded to springwheat in 1979. Four replications each of chemical and stub-

ble-mulch fallow treatments, with a plot size of 7.3-m by40.0-m, were arranged in a randomized complete block de-sign for spring and winter wheat fallow rotations. Stubble-mulch fallow consisted of sweep tillage to a depth of about0.1 m in late May and three or four additional tillage op-erations with rod weeder as needed to control weeds. Gly-phosate [A^-(phosphonomethyl)glycine], a nonselectivetranslocating herbicide, was used three to five times per fal-low season to control weeds on chemical fallow treatments.Herbicide application rates ranged from 0.4 to 0.8 kg/ha,depending on weed species and climatic conditions, andusually coincided with tillage operations on stubble-mulchfallow.

Soil water contents to a depth of 1.70 m, in 0.20-m in-crements, were measured by use of the neutron-scatter tech-nique. The first measurement was at the 0.20-m depth andaccounted for water in the upper 0.30 m of soil. Soil watercontents were determined for the 1979 to 1980 and 1981 to1982 14-month fallow periods for winter wheat and 1979 to1981, 1980 to 1982, and 1981 to 1983 21-month fallow pe-riods for spring wheat. The 14-month fallow began in lateJuly; continued through the winter and summer months un-til late September; whereas the 21-month fallow began inmid-August, continued through two winters and ended inearly May. During the 1979 to 1981 fallow period, soil watercontents were not measured until May 1980 and, becausethe amount of spring wheat residue was the same for 14-and 21-month fallow, data were combined until seeding win-ter wheat in September. Soil water contents for remainingfallow periods were measured periodically from harvest un-til seeding the next crop, except when soils were frozen orcovered with snow.

Quantities of surface residue were measured during thesummer-fallow period by sampling two 1-m2 samples per

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(B), and 1981 to 1983 21-month (C) fallow periods.

Page 3: Chemical and Stubble-Mulch Fallow Influences on Seasonal Soil Water Contents1

730 SOIL SCI. SOC. AM. J., VOL. 49, 1985

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Fig. 2. The 1979-1981 combined 14- and 21-month fallow soil water contents as influenced by chemical (CF) and stubble-mulch (SM) fallowto 0.30-m (A) and 1.70-m (B) soil depths and precipitation events for that period.

plot as described by Whitfield et al. (1962). Residue mea-surements were not made during the 1980 to 1982 springwheat fallow period because less than 0.6 Mg/ha of residuewas present at harvest.

Precipitation was measured adjacent to the study using astandard 203-mm weighing rain gauge. Least significant dif-ference (LSD) was used to determine statistical differences(Steel and Torrie, 1960).

RESULTSTotal precipitation for the 1979 to 1980 and 1981

to 1982 14-month periods were 62 and 91%, respec-tively, of the average 424 mm precipitation (Table 1).

Table 1. Average precipitation and precipitation adjacent totillage experiments from August 1979 through April 1983.

Avg.1949-1983 1979 1980 1981 1982 1983

—————————————————— nun ——————————————————

JanuaryFebruaryMarchAprilMayJuneJulyAugustSeptemberOctoberNovemberDecember

109

13295272454233221111

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112586

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155

272591414015201115

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17

83

121

Total precipitation for the 1979 to 1981, 1980 to 1982,and 1981 to 1983 21-month fallow periods were70, 113, and 94%, respectively, of the average 529 mmprecipitation. Considerable variation from averagemonthly precipitation occurred during the study.

The dry 1979 to 1981 period is reflected in the 12and 19% losses in surface residue from May throughAugust 1980 for chemical and stubble-mulch fallow,respectively (Fig. 1A). The combined 14- and 21-monthfallow period data for chemical and stubble-mulch fal-low indicate no significant differences in soil watercontents to either the 0.30- or 1.70-m soil depth (Fig.2A and B). No appreciable increase in soil water con-tents to the 1.70-m soil depth occurred from April toearly August, then 64 mm of rain fell on 17 Aug. 1980,which increased the soil water contents by 0.04 m3/m3. Soil water loss during the second winter of the 21-month fallow was minimal (0.01 m3/m3 to 1.70-m soildepth).

Most of the soil water gain to the 0.30- and 1.70-msoil depths during the 1980 to 1982 fallow period oc-curred after harvest through October (Fig. 3A and B).This was probably due to above-average precipitationfrom August through October (175 mm). A loss of0.01 m3/m3 soil water to the 1.70-m soil depth oc-curred between 24 June and 1 Oct. 1981. A gain insoil water of 0.01 m3/m3 occurred during the secondwinter. There were no significant differences in soilwater contents between chemical and stubble-mulch

Page 4: Chemical and Stubble-Mulch Fallow Influences on Seasonal Soil Water Contents1

TANAKA: CHEMICAL AND STUBBLE-MULCH FALLOW INFLUENCES ON SOIL WATER 731

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Fig. 3. The 1980 to 1982 21-month fallow soil water contents as influenced by chemical (CF) and stubble-mulch (SM) fallow to 0.30-m (A)and 1.70-m (B) soil depths and precipitation events for that period.

fallow plots because of the low quantities of surfaceresidue (<0.6 Mg/ha). Water losses due to tillage werenot detectable in the surface 0.30 m of soil.

Winter wheat plots had more surface residue thanspring wheat plots for the same treatment and timeperiod (Fig. IB and C). Stubble-mulch tillage de-creased residue throughout fallow with greatest de-creases occurring in June and July when 70 and 73%of surface residue on winter and spring wheat plots,respectively, was lost due to tillage and decomposi-tion. Chemical fallow plots, for the same months, lost10 and 5% of the residue for winter and spring wheat,respectively. At the end of fallow, chemical fallow plotshad 2.5 and 2.0 times more surface residue than stub-ble-mulch fallow plots for winter and spring wheat,respectively. Chemical fallow retained more winterwheat stubble and resulted in significantly greater soilwater contents to the 0.30-m soil depth from Juneuntil seeding in mid-September than stubble-mulchfallow (Fig. 4A). Not tilling resulted in more soil waterto the 0.30-m soil depth than did stubble-mulch til-lage. This provided favorable seedzone soil water toestablish a winter wheat crop. However, no significantdifferences in profile soil water contents or soil watercontents to 1.70-m soil depth occurred between chem-ical and stubble-mulch fallow (Fig. 4B). The major soilwater gain to 1.70 m for 14-month fallow was after

harvest and over winter with little gain during sum-mer.

No significant differences in soil water contents fortillage treatments occurred during 1981 to 1983 21-month fallow to a soil depth of 0.30 or 1.70 m (Fig.5A and B). Soil water gain, 0.13 and 0.06 m3/m3 for0.30-and 1.70-m soil depths, respectively, occurred af-ter harvest and over the first winter. The soil watercontents from July through September decreased 0.02m3/m3 to the 0.30-m soil depth while it remained staticto the 1.70-m soil depth. No change in soil water con-tents occurred over the second winter.

DISCUSSIONQuantities of surface residue after harvest during

the study period were about average for the northernGreat Plains and ranged from 0.6 to 3.5 Mg/ha withabout one-half of the residue standing and the otherhalf laying flat on the soil surface (Aase and Siddoway,1980, 1981a, 1981b). The 0.6 Mg/ha of residue wasproduced during 1980 when limited precipitation wasreceived during the growing season (Table 1). Re-search in the central Great Plains suggests that a 50:50mix of standing and flat residue may be the most ef-fective residue combination to minimize soil waterlosses (Good and Smika, 1978; Fenster and Peterson,1979; Smika, 1983). However, chemical fallow in the

Page 5: Chemical and Stubble-Mulch Fallow Influences on Seasonal Soil Water Contents1

732 SOIL SCI. SOC. AM. J., VOL. 49, 1985

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Fig. 4. The 1981 to 1982 14-month fallow soil water contents asinfluenced by chemical (CF) and stubble-mulch (SM) fallow to0.30-m (A) and 1.70-m (B) soil depths and precipitation eventsfor that period.

northern Great Plains did not significantly increasesoil water contents above that of stubble-mulch fallowto a 1.70-m soil depth (Fig. 2B, 3B, 4B and 5B). Quan-tities of surface residue > 2.5 Mg/ha may be neededfor significant differences in soil water contents be-tween chemical and stubble-mulch fallow (Fig. 4A and5A). Also, chemically fallowing winter wheat residuehas a greater potential for increasing soil water storagethan chemically fallowing spring wheat residue be-cause winter wheat produces more residue than springwheat and has a shorter fallow period (Fig. 1A, B, andC). In addition, more winter wheat stubble remainsstanding than spring wheat stubble during fallow (datanot shown).

Large quantities of surface residue reduce soil waterevaporation rates but the constant rate evaporationtime is appreciably lengthened. With continued drying,cumulative evaporation for bare and residue-coveredsurfaces eventually become equal (Army et al., 1961;Bond and Willis, 1969). This apparently happened onthe chemical fallow treatment. For chemical fallow toeffectively store more soil water than stubble-mulchfallow, frequent precipitation during low potentialevaporation periods is necessary. In the northern GreatPlains, frequent precipitation (Caprio et al., 1980) andreduced potential evaporation occur from Aprilthrough June when 36 and 29% of total fallow precip-itation is received for winter and spring wheat fallow,respectively. It is also during this period that the first

tillage operation for stubble-mulch fallow usually oc-curs; prior to this all fallow ground is treated the same.Therefore, differences in soil water contents betweenchemical and stubble-mulch fallow methods are morelikely to occur after the first tillage operation and be-fore 1 July (Fig. 4A). After 1 July, less precipitationand high potential evaporation would reduce the ef-fectiveness of residue-covered surfaces. During the highevaporative potential part of the fallow period, up-ward movement of soil water in chemical fallow re-sulted in soil water storage equivalent to that for stub-ble-mulch fallow. A practical method to reduce soilwater losses in chemical fallow may be to create a soilmulch with shallow tillage just prior to periods of highpotential evaporation (Army et al., 1961; Willis andBond, 1971; Hammel et al., 1981). This may reduceevaporative losses by disrupting pore continuity andthus restrict upward movement of soil water (Blackand Power, 1965).

Soil water gains were greatest after harvest and overthe first winter when soils were dry, residue had notdecomposed, and evaporation rate was low. In gen-eral, losses of soil water usually occurred during thesummer for chemical and stubble-mulch fallow. Forfallowed spring wheat stubble, the second winter didnot result in soil water gain for chemical fallow eventhough about one-fourth of the residue was standingprior to winter. This is similar to the finding of Haasand Willis (1962) for spring wheat fields that were blackfallowed following harvest.

The data indicate that precipitation frequency anddistribution are just as important as quantity and po-sition of surface residue. For more soil water to beeffectively stored with chemical fallow in the northernGreat Plains, average or above-average precipitationduring low evaporative demand periods and more than2.5 Mg/ha of surface residue may be needed to permitdeep water penetration. To reduce soil water lossesfrom chemical fallow due to upward movement dur-ing high potential evaporation periods, shallow tillagemay be necessary. The data also suggest that researchconducted in other areas of the Great Plains may notbe applicable to the northern Great Plains due to dif-ferences in precipitation frequency and distribution,seasonal potential evaporation, and quantity of sur-face residue.

Page 6: Chemical and Stubble-Mulch Fallow Influences on Seasonal Soil Water Contents1

TANAKA: CHEMICAL AND STUBBLE-MULCH FALLOW INFLUENCES ON SOIL WATER 733

0.30T

1981

Fig. 5. The 1981 to 1983 21-month fallow soil water contents as influenced by chemical (CF) and stubble-mulch (SM) fallow to 0.30-m (A)and 1.70-m (B) soil depths and precipitation events for that period.

residue rate and placement effects. Soil Sci. Soc. Am. Proc. 33:445-448.

Brown, P.L., and D.D. Dickey. 1970. Losses of wheat straw residueunder simulated field conditions. Soil Sci. Soc. Am. Proc. 34:118-121.

Caprio, J.M., R.D. Snyder, and O.K. Grunwald. 1980. Precipitationprobabilities in Montana. Montana Agric. Exp. Stn. Bull. 712.

Fenster, C.R., and G.A. Peterson. 1979. Effects of no-tillage fallowas compared to conventional tillage in a wheat-fallow system.Research Bull. 289, Agric. Exp. Stn. University of Nebraska, Lin-coln.

French, E.W., and N. Riveland. 1980. Chemical fallow in a springwheat-fallow rotation. North Dakota Farm Research 38(1): 12-15.

Good, L.G., and D.E. Smika. 1978. Chemical fallow for soil andwater conservation in the Great Plains. J. Soil Water Conserv.33:89-90.

Greb, B.W., D.E. Smika, and A.L. Black. 1967. Effect of straw mulchrates on soil water storage during summer fallow in the GreatPlains. Soil Sci. Soc. Am. Proc. 31:556-559.

Greb, B.W., D.E. Smika, and A.L. Black. 1970. Water conservationwith stubble mulch fallow. J. Soil Water Conserv. 25:58-62.

Haas, H.J., and W.O. Willis. 1962. Moisture storage and use bydryland spring wheat cropping systems. Soil Sci. Soc. Am. Proc.26:506-509.

Haas, H.J., W.O. Willis, and J.J. Bond. 1974. Summer fallow in thenorthern Great Plains (spring wheat), p. 12-35. In Summer fallow

in the western United States. USDA Conserv. Res. Rep. 17. U.S.Government Printing Office, Washington, DC.

Hammel, J.E., R.I. Papendick, and G.S. Campbell. 1981. Fallowtillage effects on evaporation and seedzone water content in a drysummer climate. Soil Sci. Soc. Am. J. 45:1016-1022.

Johnson, W.C., and R.G. Davis. 1980. Yield-water relationships ofsummer-fallowed winter wheat. A precision study in the TexasPanhandle. Agric. Res. Results, ARR-S-5/July 1980.

Smika, D.E. 1983. Soil water changes as related to position of wheatstraw mulch on the soil surface. Soil Sci. Soc. Am. J. 47:988-991.

Smika, D.E., A.L. Black, and B.W. Greb. 1969. Soil nitrate, soilwater, and grain yield in a wheat-fallow rotation in the GreatPlains as influenced by straw mulch. Agron. J. 61:785-787.

Smika, D.E., and G.A. Wicks. 1968. Soil water storage during fallowin the central Great Plains as influenced by tillage and herbicidetreatments. Soil Sci. Soc. Am. Proc. 32:591-595.

Steel, R.G.D., and J.H. Torrie. 1960. Principles and procedures ofstatistics, p. 106-107. McGraw-Hill Inc., New York.

Whitfield, C.J., J.J. Bond, B.W. Greb, T.M. McCalla, and F.H. Sid-doway. 1962. A standardized procedure for residue sampling, p.3-9. ARS 41-68, USDA. U.S. Government Printing Office, Wash-ington, DC.

Wiese, A.F., and T.J. Army. 1960. Effect of chemical fallow on soilmoisture storage. Agron. J. 52:612-613.

Willis, W.O., and J.J. Bond. 1971. Soil water evaporation: reductionby simulated tillage. Soil Sci. Soc. Am. Proc. 35:526-529.