Conservation Tillage and Deficit Irrigation Effects on Water Use and Yield of Cotton and Corn.

Increasing pumping costs and declining well capacities in the Southern High Plains encourage producers to consider residue retaining conservation tillage practices to improve precipitation capture and increase yield. Objectives were to quantify tillage effects on i)  fallow precipitation storage for a wheat (Triticum aestivum L.) – summer crop – fallow crop rotation (WSF), and ii) yield of deficit irrigated cotton [Gossypium hirsutum (L.)] and corn (Zea mays L.). Winter wheat was sown at 4 g m^-2 in early September 2004 and 2005 using 0.25-m rows on a Pullman clay loam (fine, mixed, superactive, thermic Torrertic Paleustoll) at the USDA-ARS, Conservation and Production Res. Lab., Bushland, Texas. Cotton and corn were planted in 0.76-m rows at 24 and 15 seeds m^-2, respectively, in May 2006 and 2007. Disk, sweep, and no–till systems were used for weed control during the intervening fallow periods and herbicides were used during the growing season. Summer crops were irrigated with a linear move mid-elevation spray system at 2.5 or 5.0 mm d^-1 on ~ 10 d intervals. Fallow storage of rain increased with decreasing tillage intensity in no–till and stubblemulch treatments. Cumulative water use increased with increasing irrigation; however, tillage effects on water use varied with year and irrigation level. Crop yields were significantly greater for conservation tillage practices compared with the 20 to 35% lower disk tillage yields depending on growing season conditions. Better growing conditions during 2007 diminished the tillage effects on yields when irrigation increased from 2.5 to 5.0 mm d^-1. Increasing irrigation and conservation tillage resulted in 10 to 40% greater yield of cotton and corn in 2006 (respectively). Residue retaining conservation tillage practices increased crop water use and yield through increased fallow season soil water storage and reduced evaporation of irrigation water.