Modeling irrigation management strategies to maximize cotton lint yield and water use efficiency
Increasing pumping costs and declining well capacities in the Southern High Plains compel producers to seek irrigation strategies to maximize yield and water use efficiency (WUE), which is the ratio of yield to evapotranspiration (ET). Cotton (Gossypium hirsutum L.) is suited to deficit irrigation using wells ranging from 0.29 to 0.93 L s–1 ha–1 capacity to supply limited, 2.5 mm d–1, to complete, 8.1 mm d–1 ET replacement. Our objectives were to (i) evaluate irrigation capacity and duration effects on lint yield, and (ii) compare application strategies that maximize yield and WUE. The simulation model GOSSYM was used with 1959 to 2000 weather records from Bushland, TX, to calculate yields of cotton grown on a Pullman clay loam (fine, mixed, superactive, thermic Torrertic Paleustoll) with 50 or 100% initial available soil water. We compared all combinations of irrigation duration (4, 6, 8, and 10 wk) and capacity (for ET replacement of 2.5, 3.75, and 5.0 mm d–1 and dryland). Simulated lint yield decreased as irrigation decreased; however, yields for similar irrigation totals increased with increasing irrigation capacity. Simulated yields for cotton irrigated > 8 wk did not differ among irrigation capacities, but cotton irrigated at 5.0 mm d–1 maintained yield with earlier irrigation termination at 6 wk. Based on mean yields, we determined that spreading water to deficit irrigate a field with 2.5 mm d–1 yielded ~5% less lint than concentrating that water to irrigate smaller fields at 3.75 or 5.0 mm d–1 that were averaged with complementary (2:1 and 1:1) dryland areas.