Water budget and yield of dryland cotton intercropped with terminated winter wheat

A Texas South Plains production system for reducing wind erosion in irrigat ed cotton (Gossypium hirsutum L.), a low-residue crop, is to plant winter w heat (Triticum aestivum L.) after cotton harvest, chemically terminate the wheat in the spring, and plant cotton using conservation tillage. The termi nated wheat-cotton system (TWC) utilizes fall rain to grow wheat residue, T his system has increased irrigated cotton lint yields compared with continu ous clean-tillage cotton (CCC), but there is limited information on the ann ual water budget and adaptability of TWC under dryland conditions. This stu dy compares CCC and TWC effects on (i) runoff and infiltration of rain, (ii ) the annual water balance, and (iii) cotton hint yield under dryland condi tions. The water budget of TWC end CCC was measured in 3-by 30-m subplot wa tersheds from May 1992 to December 1995 on an Amarillo sandy loam (fine-loa my, mixed, thermic Aridic Paleustalf) at Wellman, TX, Compared with CCC plo ts, the TWC residue reduced average annual runoff by 43 mm, but increased a verage fallow water use by 28 mm (tor growing wheat), The use of TWC did no t significantly (P = 0.05) increase either water conservation or cotton lin t yields compared with CCC. Cotton establishment was problematic due to lim ited soil water at planting in 1993 for TWC and CCC. This prevented 1994 TW C cotton establishment, thus offsetting improved establishment in 1992, whe n residue protected cotton seedlings during above-average rain. In semiarid regions, inadequate soil water for crop establishment is an uncontrolled r isk with dryland TWC production. Because no significant gains in mater stor age or cotton lint yield were observed under dryland conditions with TWC co mpared with CCC, undertaking the greater crop establishment risk with TWC c otton production is not recommended in the Tex-as South Plains.