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

Residue management to increase fallow precipitation storage and reduce growing season evaporation limited potential yield reduction by off setting a portion of the decreasing irrigation well capacity of the declining Ogallala Aquifer in the southern High Plains. A 3-yr dryland rotation of wheat (Triticum aestivum L.) followed by corn (Zea mays 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) at Bushland, TX (35 degrees 11' N, 102 degrees 6' W). Study objectives were to quantify disk (DT), stubble-mulch (SM), or no (NT)-tillage effects on precipitation storage during wheat fallow and subsequent use for grain yield by deficit irrigated corn. The 4-yr mean soil water after fallow increased from 14 to 50 mm for SM and NT compared with DT. Measured growing season water use ranged from similar to 54 to 64% of the estimated corn water use (ETc) at the 2.5 mm d(-1) irrigation capacity and from 76 to 85% at 5.0 mm d(-1) irrigation with corresponding grain yields ranging from crop failure to similar to 7.4 Mg ha(-1). We conclude that residue retaining conservation tillage increased soil water storage during fallow. We attributed greater corn yield with conservation tillage to likely increased transpiration made possible by reducing early growing season evaporation. Increased soil water and greater transpiration using conservation tillage practices did not off set corn ET reduction imposed by either deficit irrigation capacity and resulted in unprofitable crop yield reductions.