Agronomic and Economic Impacts of Tillage and Rotation on Wheat and Sorghum

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The predominant crop in the central Great Plains is winter wheat (Triticum aestivum L.) grown in a wheat-fallow (WF) rotation. However summer crops, such as grain sorghum [Sorghum bicolor (L.) Moench] or corn (Zea mays L.), grown in a wheat-summer crop-fallow rotation are increasingly popular. Tillage is decreasing as reduced tillage (RT) and no-tillage (NT) systems are used more extensively in intensive cropping systems. This field study quantified the effects of increasing cropping intensity and reducing tillage on soil water dynamics, wheat and grain sorghum production and profitability, and the sorghum yield necessary to ensure greater profitability with a wheat-sorghum-fallow (WSF) rotation than with WF. Cropping systems were WF, WSF, and continuous wheat (WW). From 1991 to 1995 all crops were grown under NT, and WF and WSF also were grown under RT. Reduction in tillage had little effect on soil water storage prior to planting of wheat or sorghum. Precipitation capture during fallow tended to be greater with WSF than WF (35 vs. 29%). Wheat yields were similar for WF and WSF (46 vs. 47 bu/acre), with WW yields being about 45% less. Tillage had little impact on wheat yields, but sorghum yields were 23% greater with NT than RT (59 vs. 48 bu/acre). Water use efficiency (WUE) was greater for sorghum than wheat, and NT increased sorghum WUE by 25% compared with RT (205 vs. 167 lb/in.). The quantity of wheat straw was similar for WF and WSF, with about 145 lb of straw/bu of wheat yield, which is much greater than the commonly used value of 100 lb of straw/bu. Production costs were $14 to 19/acre greater with NT than RT for wheat, primarily because of higher weed control costs, but production costs were similar for NT and RT sorghum. Economic returns were similar for WF-RT, WSF-RT, and WSF-NT at about $22 to 27/acre compared with $10 to 13/acre for WF-NT and WW-NT. The sorghum yield to make WSF more profitable than wheat depends upon relative grain prices, yield, and production costs; in this study, sorghum yields of 55 to 60 bu/acre were required before WSF was as profitable as WF.