Cropping System Influence on Planting Water Content and Yield of Winter Wheat

wheat yields were reduced by 79 kg ha 1 for every centimeter that soil water at wheat planting was reduced by Many dryland producers in the central Great Plains of the USA sunflower (Helianthus annuus L.) ahead of wheat in express concern regarding the effect that elimination of fallow has on soil water content at winter wheat (Triticum aestivum L.) planting rotation. In southwestern Kansas, Norwood (2000) simiand subsequent yields. Our objectives were to quantify cropping syslarly showed lower winter wheat yields when the previtem effects (fallow weed control method and crop sequence), including ous crop was sunflower or soybean compared with corn corn (Zea mays L.) (C) and proso millet (Panicum miliacium L.) (M), or grain sorghum [Sorghum bicolor (L.) Moench]. These on soil water at winter wheat planting and subsequent grain yield, and reductions in wheat yield were related to lower soil to determine the frequency of environmental conditions which would water at planting. Lyon et al. (1995) showed that soil cause wheat yield to drop below 2500 kg ha 1 for various cropping water at planting was strongly correlated with yield of systems. Crop rotations evaluated from 1993 through 2001 at Akron, short season summer crops [pinto bean (Phaseolus vulCO, were W-F, W-C-F, W-M-F, and W-C-M (all no-till), and W-F garis L.), proso millet] but only weakly related to yield (conventional till). Yields were correlated with soil water at planting: of long season summer crops (sunflower, grain sorghum, kg ha 1 373.3 141.2 cm (average and wet years); kg ha 1 897.9 39.7 cm (dry years). Increasing cropping intensity to two corn). They attributed this result in part to shorter seacrops in 3 yr had little effect on water content at wheat planting and son crops having more soil water available at the critical subsequent grain yield, while continuous cropping and elimination of reproductive growth stage than longer season crops, fallow reduced soil water at planting by 11.8 cm and yields by 450 which used much of the initial soil water for stover to 1650 kg ha 1, depending on growing season precipitation. No-till production and did not have it available for grain develsystems, which included a 12to 15-mo fallow period before wheat opment. planting nearly always produced at least 2500 kg ha 1 of yield under In addition to differences in previous crop water use, normal to wet conditions, but no cropping system produced 2500 kg soil water content at wheat planting can also be affected ha 1 under extremely dry conditions. by differences in tillage and crop residue effects on precipitation storage efficiency. Precipitation storage efficiency increases as tillage is reduced during the sumT traditional wheat–fallow production system used mer fallow period before wheat planting (Smika and in the central Great Plains of the USA was develWicks, 1968; Tanaka and Aase, 1987; Norwood, 1999). oped in the 1930s as a strategy to minimize incidence of Crop residues reduce soil water evaporation by shading crop failures resulting from erratic precipitation (Hinze the soil surface and reducing convective exchange of and Smika, 1983). The use of herbicides to control weeds water vapor at the soil–atmosphere interface (Greb et in this system reduced or eliminated tillage, and led to al., 1967; Aiken et al., 1997; Van Doren and Allmaras, greater precipitation storage efficiencies, such that more 1978). Additionally, reducing tillage and maintaining frequent cropping could be successfully employed (Halsurface residues reduce precipitation runoff and invorson and Reule, 1994; Peterson et al., 1993; Anderson crease infiltration, thereby increasing precipitation storet al., 1999; Norwood et al., 1990; Smika, 1990; Farahani age efficiency (Unger and Stewart, 1983). et al., 1998). Both producers and agricultural lenders would like While more intensive cropping is gradually replacing to have a means of assessing the risk level that might W-F in the central Great Plains, many producers still be incurred in moving from conventional wheat–fallow express concern regarding the effect that more frequent production systems to more intensively cropped no-till cropping has on soil water content at planting and subsesystems. Part of that risk assessment involves quantifyquent winter wheat yields. Previous research has shown ing the effects of cropping system on wheat yields. Thererelationships between available soil water and yield of fore, the objectives of this study were to (i) quantify some crops. Nielsen et al. (1999) reported that winter effects of cropping system (crop sequence and fallowseason weed-control method [i.e., tillage vs. no-till]) on D.C. Nielsen, M.F. Vigil, R.A. Bowman, and J.G. Benjamin, USDAsoil water content at winter wheat planting and subseARS, Central Great Plains Res. Stn., 40335 County Road GG, Akron, quent effects on grain yield, and (ii) determine freCO 80720; R.L. Anderson, USDA-ARS, Northern Grain Insects Res. quency of environmental conditions that cause wheat Lab., 2923 Medary Ave., Brookings SD 57006; and A.D. Halvorson, USDA-ARS, Soil–Plant–Nutrient Research Unit, P.O. Box E, 301 S. Howes, Ft. Collins, CO 80522. Received 21 Jan. 2002. *Corresponding Abbreviations: CT, conventional tillage; W-C-F, wheat–corn–fallow; author (dnielsen@lamar.colostate.edu). W-C-M, wheat–corn–millet; W-F, wheat–fallow; W-M-F, wheat–millet– fallow; NT, no-till. Published in Agron. J. 94:962–967 (2002).