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

Tbe 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-faliow (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. Research QuestionThe predominant crop in the central Great Plains is winter wheat grown in a wheat-fallow (WF) rotation, although more intensive cropping (i.e., wheat-summer crop-fallow) may be more profitable. This research quantified soil water dynamics, crop production, and profitability of wheat-fallow and wheat-grain sorghum-fallow (WSF) rotations under reduced tillage (RT) and no-tillage (NT) and determined the minimum sorghum yield needed to make WSF as profitable as WF. Literature SummaryLow precipitation and high evaporation potential limit yields of dryland crops in the central Great Plains; thus, fallow is used to increase soil water storage and enhance yield. Compared with conventional tillage (CT) systems, maintaining surface crop residue cover with RT or NT systems can reduce evaporation and enhance soil water storage. Several studies have shown increased grain sorghum yields with reduced tillage intensity but minimal impact on yield of winter wheat. The impact of increased cropping intensity on profitability has been mixed. WSF was more profitable than WF in western Kansas but less profitable in southeastern Colorado. Little information is available on the sorghum yields required to make WSF more profitable than WF. Also, the majority of previous economic analyses included federal program payments. With the current policy environment, economic analyses of different cropping systems without government payments are more appropriate. Study DescriptionWF and WSF rotations using RT and NT practices along with NT continuous wheat (WW) were evaluated for 5 yr with all phases of each rotation present each year. The study site was in west central Kansas on a Richfield silt loam soil. Profile soil water content was determined at planting and harvest of each crop. Other measurements included grain yield, yield components, and biomass production. An economic analysis used costs of cultural practices typical for the region and average grain prices to determine relative profitability of each system and the sorghum yield required to make WSF as profitable as WF. Applied QuestionsWhat effects do tillage and cropping intensities have on soil water at planting? Reduction in tillage had little effect on soil water storage prior to planting of wheat or sorghum. Available soil water at wheat planting was the same for WF and WSF at about 10 in. (Table 1). Increasing cropping intensity to WW reduced available soil water by about 50%. What effects do tillage and cropping intensities have on grain yield? Wheat yields were similar for WF and WSF, and WW yields were about 45% less (Table 1). Tillage had little effect on wheat yields, but sorghum yields were 23% greater with NT than RT. What effects do tillage and cropping intensities have on costs and profitability? Production costs were greater with NT than RT for wheat, but similar for NT and RT sorghum. Economic returns were similar for WF-RT, WSF-RT, and WSF-NT at about $22 to 27/tillable acre and much greater than returns for WF-NT or WW-NT ($10–13/acre). What sorghum yield is required to make WSF as profitable as WF? The sorghum yield to make WSF as profitable as WF depends upon relative grain prices, yields, and production costs (Fig. 1). In this study, sorghum yields of 55 to 60 bu/acre were required for WSF to be as profitable as WF. Fig. 1Sorghum yield required in RT/NT-WSF at several wheat/ sorghum prices for returns to equal those of RT-WF, based on analyses at Tribune, KS. Values in parentheses are sorghum/wheat price ratios. Table 1Grain yield and available soil water at planting as affected by tillage and rotation, 1991–1995, Tribune, KS. Cropoing systemGrain yieldAvailable soil waterbu/acrein/8-ft profileWheat WF-RT4810.4 WF-NT4410.4 WSF-RT4710.8 WSF-NT4610.1 WW-NT255.6 LsD₀.₀₅ 91.1Grain sorghum WSF-RT4810.8 F-NT5911.3 LsD₀.₀₅ 3NS