PROFILE WATER DISTRIBUTION AND GRAIN-YIELD AS AFFECTED BY CROPPING SYSTEM AND TILLAGE

Yields of dryland crops are limited by precipitation in the Great Plains. Winter wheat (triticum aestivum L.) grown in the wheat-fallow (WF) system (one crop in 2 yr) occupies the greatest area. The use of grain sorghum [Sorghum bicolor (L.) Moench] in the wheat-sorghum-fallow (WSF) system (two crops in 3 yr) is becoming popular. Other cropping systems include sorghum-fallow (SF) and continuous sorghum (SS). Research was conducted in the central Great Plains at Garden City, KS, from 1987 through 1992 to quantify soil water storage and use and grain yield in the WF, WSF SS, and SF systems in order to develop more efficient dryland grain production systems. No tillage (NT) and conventional tillage (CT) were compared in the WF and WSF systems. Available soil water at planting and harvest was measured in 0.3-m increments to a depth of 1.5 m, and grain yield and water use efficiencies were determined. Water moved deeper in the profile under NT. Compared with CT, twice as much water was stored due to NT in the WSF sorghum profile as in the WF and WSF wheat profiles. An average of 62% of the additional water was found below 09 m. As much water was stored in the 11-mo fallow period prior to WSFNT sorghum as was stored in the 15- and 19-mo fallow periods of WF and SF. No tillage resulted in yield increases 17% of the time in WF, 34% of the time for wheat in WSF, and 60% of the time for sorghum in WSF. For sorghum, the yield of SF was similar to that of WSFNT, whereas SS had the lowest grain yield per planted hectare. Efficient storage of precipitation in WSF prior to NT sorghum and increased sorghum yield make the WSFNT system superior to other systems in this study.