Sorghum Management Practices Suited to Varying Irrigation Strategies: A Simulation Analysis

Increasing pumping costs and declining well capacities in regions like the Southern High Plains of Texas are requiring producers to adapt cropping practices for usewith irrigation levels that vary between complete replacement of crop evapotranspiration (ET) to none (i.e., dryland production). Grain sorghum [Sorghum bicolor (L.) Moench] is a crop suited to both dryland and various deficit irrigation production systems. Our objectives were to (i) identify cultural practices (planting date, population, and cultivar maturity) that maximize sorghum grain yield for widely varying irrigation strategies; and (ii) consider effective means to allocate available water among irrigation strategies that maximizes the ratio of yield to ET, that is, water use efficiency (WUE). Using the model SORKAM and long-term (1958–1999) weather records from Bushland, TX, we simulated sorghum grain yields on a Pullman soil (fine, mixed, superactive, thermic Torrertic Paleustoll) under dryland (rain) and three deficit irrigation levels (rain 1 irrigation 5 2.5, 3.75, or 5.0 mm d) for all combinations of planting date (mid-May, 15 May; early June, 5 June; and late June, 25 June), cultivar maturity (early, 95 d; medium, 105 d; late, 120 d), and plant density (12 and 16 plants m). For 2.5mmd irrigation level, simulated grain yields were maximized with either early or medium-maturing cultivars planted in early June. In contrast, simulated sorghum yield and WUE increased with a mid-May planting date and later-maturing cultivars for irrigation levels of 3.75 and 5.0mmd.We conclude that spreading water to uniformly irrigate a field with 2.5 mm d produces |16% less grain than concentrating the same water resources to variably irrigate a field at 3.75 or 5.0 mm d with complementary (2:1 and 1:1)