Seeding practices, cultivar maturity, and irrigation effects on simulated grain sorghum yield

Grain sorghum [Sorghum bicolor (L.) Moench] is adapted for use in dryland and irrigated cropping systems on the southern High Plains, Irrigation in this region relies on the declining Ogallala aquifer, and applications are transitioning from full to deficit evapotranspiration replacement. Our objective was to identify optimum planting date, population, row spacing, and cultivar maturity combinations to maximize grain sorghum yield using the SORKAM model and long-term (1958-1999) weather records at Bushland, TX, for a Pullman soil (fine, mixed, superactive, thermic Torrertic Paleustoll) with reduced irrigation. Grain sorghum growth and yield was simulated under dryland and deficit- or full-irrigation conditions (rain + irrigation = 2.5 or 5.0 mm d(-1)) for all combinations of planting date (15 May, 5 June, 25 June), cultivar maturity (early, 95 d; medium, 105 d; late, 120 d), population (12 and 16 plants m(-2)), and row spacing (0.38 and 0.76 m). Simulated grain yield was unaffected by planting population but increased 7% for narrow compared with wide row spacing independent of other treatment effects. Results suggest two alternative management practices to optimize yield for the southern High Plains depending on potential irrigation capacity: (i) where rain plus supplemental irrigation was < 0.2.5 mm d(-1), plant early-maturing cultivars during June and (ii) where rain plus supplemental irrigation approaches 5.0 min d(-1), plant late-maturing cultivars on 15 May. Early-maturity cultivars planted on 5 June were better adapted to dryland and deficit irrigation for optimum grain yield on a southern High Plains Pullman soil.