Ground water and surface water under stress

Presented at Ground water and surface water under stress: competition, interaction, solutions: a USCID water management conference on October 25-28, 2006 in Boise, Idaho.Includes bibliographical references.Irrigated crop production in the Texas High Plains is dependent on the Ogallala Aquifer, which has declined by up to 50 percent in some areas since irrigation development began in the 1930-40s. About 6.5 million acre-feet (ac-ft) of water was pumped to irrigate 4.6 million acres in 2000, with most irrigation demand being for corn and cotton production. Cotton is produced primarily in the Southern Texas High Plains, with corn and winter wheat comprising most of the irrigated area in the Northern Texas High Plains. However, cotton production is expanding northward again and replacing corn in some areas because both crops currently have similar revenue potential but cotton has about half the irrigation water requirement, and may result in profitable yields under dryland and deficit irrigated conditions. In the Northern Texas High Plains, combined annual irrigation demand for corn and cotton could be reduced from 2.6 to 2.0 million ac-ft by replacing 50 percent of the irrigated corn area with cotton, and combined irrigation demand could be reduced to 1.6 million ac-ft if cotton irrigation applications were reduced to 50 percent of full crop evapotranspiration minus rainfall. In the Southern Texas High Plains, annual irrigation demand for cotton could be reduced from 1.4 to 1.0 million ac-ft if overall irrigations were reduced to 50 percent of full crop evapotranspiration minus rainfall. Deficit irrigation results in some yield penalty; however, if the crop is relatively drought tolerant, this may be offset somewhat by the reduced energy costs of pumping