Water Budget and Yield of Dryland Cotton Intercropped with Terminated Winter Wheat

A Texas South Plains production system for reducing wind erosion in irrigated cotton (Gossypium hirsutum L.), a low-residue crop, is to plant winter wheat (Triticum aestivum L.) after cotton harvest, chemically terminate the wheat in the spring, and plant cotton using conservation tillage. The terminated wheat–cotton system (TWC) utilizes fall rain to grow wheat residue. This system has increased irrigated cotton lint yields compared with continuous clean-tillage cotton (CCC), but there is limited information on the annual water budget and adaptability of TWC under dryland conditions. This study compares CCC and TWC effects on (i) runoff and infiltration of rain, (ii) the annual water balance, and (iii) cotton lint yield under dryland conditions. The water budget of TWC and CCC was measured in 3- by 30–m subplot watersheds from May 1992 to December 1995 on an Amarillo sandy loam (fine-loamy, mixed, thermic Aridic Paleustalf) at Wellman, TX. Compared with CCC plots, the TWC residue reduced average annual runoff by 43 mm, but increased average fallow water use by 28 mm (for growing wheat). The use of TWC did not significantly (P = 0.05) increase either water conservation or cotton lint yields compared with CCC. Cotton establishment was problematic, due to limited soil water at planting in 1993 for TWC and CCC. This prevented 1994 TWC cotton establishment, thus offsetting improved establishment in 1992, when residue protected cotton seedlings during above-average rain. In semiarid regions, inadequate soil water for crop establishment is an uncontrolled risk with dryland TWC production. Because no significant gains in water storage or cotton lint yield were observed under dryland conditions with TWC compared with CCC, undertaking the greater crop establishment risk with TWC cotton production is not recommended in the Texas South Plains.