Agronomic and economic impacts of tillage and rotation on wheat and sorghum

The predominant crop in the central Great Plains is winter wheat (Triticum aestivum L.) grown in a wheat-fallow (WF) rotation. However summer crops, s uch as grain sorghum [Sorghum bicolor (L.) Moench] or corn (Zea mays L.), g rown in a wheat-summer crop-fallow rotation are increasingly popular. Tilla ge is decreasing as reduced tillage (RT) and no-tillage (NT) systems are us ed more extensively in intensive cropping systems. This field study quantif ied the effects of increasing cropping intensity and reducing tillage on so il water dynamics, wheat and grain sorghum production and profitability, an d 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 e ffect on soil water storage prior to planting of wheat or sorghum. Precipit ation capture during fallow tended to be greater with WSF than WF (35 vs. 2 9%). 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 fbr sorghum than wheat, and NT increased sorghum WUE by 25% compared with RT (205 vs. 167 lb/in.). The quantity of w heat straw was similar for WF and WSF, with about 145 Ib of straw/bu of whe at yield, which is much greater than the commonly used value of 100 lb of s traw/bu. Production costs were $14 to 19/acre greater with NT than RT for w heat, 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 f or WENT and WW-NT The sorghum yield to make WSF more profitable than wheat depends upon relative grain prices, yield, and production costs; in this st udy, sorghum yields of 55 to 60 bu/acre were required before WSF was as pro fitable as WF.