Increasing Yield of Deficit Irrigated Cotton and Corn with Conservation Tillage.

Conservation tillage retains residue and increases precipitation capture, which could reduce irrigation from the Ogallala Aquifer. Our objective was to quantify disk, stubble-mulch, and no -tillage effects on water use and yield of deficit irrigated corn (Zea mays L.) and cotton (Gossypium hirsutum L.) grown in rotation with wheat (Triticum aestivum L.) and intervening fallow on a Pullman soil (fine, mixed, superactive, thermic Torrertic Paleustoll) at the USDA-ARS Conservation and Production Research Laboratory, Bushland, TX. For four cropping seasons beginning in 2006, we seeded separate blocks of cotton and corn at 12 and 9 plants m^-2, respectively, in 0.76-m rows during mid-May following a 10-month fallow after wheat. Using a lateral move mid-elevation sprinkler system, crops were irrigated in strips receiving ~ 25 or 50 mm every 10-14 days to represent limited well pumping capacities common to the Southern High Plains. We measured precipitation and soil water to determine crop water use in relation to yield. No-tillage reduced evaporation and increased soil water stored during fallow by > 40 mm compared with sweep and disk tillage. Both corn and cotton evapotranspiration (ET) increased with increasing irrigation, but the shorter cotton crop realized greater ET with residue retaining stubble-mulch and no-tillage practices. Compared with disk tillage, no-tillage residue increased mean corn yield by 1.25 Mg ha^-1 or 86% at the ~2.5 mm d^-1 irrigation rate and 25% from 3.86 to 4.82 - Mg ha^-1 for the ~5.0 mm d^-1 irrigation rate. Lint yields did not vary by irrigation rate during any year, but no-tillage increased mean lint yield 0.34 Mg ha^-1 or ~50% compared with disk tillage. We conclude that no-till residue repartitioned ET by reducing growing season evaporation and increasing crop transpiration, which increased crop water use efficiency and yields.