Residue Management Effects on Water Use and Yield of Deficit Irrigated Cotton

The declining saturated thickness of the Ogallala Aquifer beneath the southern High Plains decreases irrigation well capacity and necessitates conservation of precipitation for crop use. A 3-yr dryland crop rotation of wheat (Triticum aestivum L.) followed by cotton (Gossypium hirsutum L.) with intervening 10-mo fallow periods was adapted for use with deficit irrigation of 2.5 and 5.0 mm d(-1) capacities on a Pantex silty clay loam (fine, mixed, superactive, thermic Torrertic Paleustoll) managed with disk (DT), stubble-mulch (SM), or no (NT)-tillage at Bushland, TX (35.183 degrees N, 102.1 degrees W). Study objectives were to quantify tillage effects on soil water storage during wheat fallow and any continued effects on water use and yield by deficit irrigated cotton. Compared with DT, wheat residue cover increased mean fallow precipitation storage by similar to 15 mm for SM and 50 mm with NT based on significant differences in 3 of 4 yr. The significant differences in cotton water use between irrigation capacities totaled from 70% to similar to 100% of the estimated evapotranspiration, ET. Measured growing season water use decreased with decreasing residue cover in the order NT > SM > DT. Cotton lint yield did not vary between irrigation capacities, but increased with NT by similar to 50% or 450 kg ha(-1) over DT. Yields for DT cotton irrigated at 5 mm d(-1) were typically less than for NT and SM cotton irrigated at 2.5 mm d(-1). Lint yield for NT management was significantly greater than DT, which we attributed to reduced evaporation and greater transpiration with NT residue.