Factors related to dryland grain sorghum yield increases: 1939 through 1997

Grain yields of dryland (nonirrigated) grain sorghum [Sorghum bicolor (L.) Moench], a major crop in the southern Great Plains, more than tripled in st udies at the USDA-ARS Conservation and Production Research Lab., Bushland. TSI during the period from 1939 to 1997. Our objectives were to document th e yield increases that occurred and to determine factors primarily responsi ble for the yield increases. Factors evaluated were annual precipitation, g rowing-season rainfall, soil water content at planting, soil water use, gro wing-season evapotranspiration, and pm of record. For the report, we assemb led 502 treatment-years of grain yield data from 37 studies. For the 1939-1 997 period, grain yields increased about 50 kg ha(-1) annually. Yields incr eased 139% during the 1956-1997 period, with 46 of those percentage units r esulting from use of improved hybrids, based on results of a uniformly mana ged 40-year study, The remaining 93 percentage units for that period were a ttributed to of her factors. primarily to soil water at planting. increases in soil water at planting resulted from changes in management practices wi th time, mainly the adoption of improved crop residue management practices after about 1970.