CROPPING AND TILLAGE SYSTEMS FOR DRYLAND GRAIN PRODUCTION IN THE SOUTHERN HIGH-PLAINS

Low precipitation and high evaporative potential limit yields of dryla nd crops in the semiarid Southern High Plains. Improved residue manage ment can reduce evaporation and improve water conservation. We compare d no-tillage (NT) and stubble mulch (SM residue management effects fro m 1984 to 1993 on leveled minibenches at Bushland, TX, using winter wh eat (Triticum aestivum L.)-fallow (WF), continuous wheat (CW), wheat-s orghum [Sorghum bicolor (L.) Moench]-fallow (WSF), and continuous sorg hum (CS) systems. The soil was a Pullman clay loam (fine, mixed, therm ic Torrertic Paleustoll). Our objective was to quantify and compare so il water storage, crop water use, and grain production in order to ide ntify the most water-efficient production system. Relative to SM manag ement, NT management of wheat residues increased average soil water co ntents at planting of the next crop by 22 mm with WSF, 15 mm with WF, and 29 mm with CW; it was not as effective with sorghum residues. Mean grain yields were not affected by residue management on any cropping system, because the additional water stored with NT management was sli ght in relation to seasonal evapotranspiration. Cropping systems had m ajor effects on grain yield and production. Fallow systems (WSF, WF) n ormally resulted in higher yields than the corresponding annual croppi ng system (CW, CS). However, when grain production was adjusted to an annual basis including fallow time, the CS system was most efficient a t using precipitation, producing 92% more grain than WSF, 240% more th an CW, and 320% more than WF. Grain production was more than twice as great with sorghum than with wheat, due to greater biomass production and a 33% greater harvest index. Although wheat is the major dryland c rop in the Southern High Plains, sorghum seems much better adapted to the region's predominant pattern of late spring-summer rainfall.