WATER RELATIONS AND YIELD OF WINTER WHEAT GROWN UNDER THREE WATER REGIMES IN THE HIGH PLAINS*

Five cultivars of winter wheat (Triticum aestivum L. em. Thell.) were grown in the field under two ridge-and-furrow irrigation treatments in the Panhandle of Oklahoma to determine if yields could be increased by applying irrigation water at different times in the spring than it is normally applied. The plants grown under the "modified " irrigation schedule received 15.2 cm of irrigation water in the spring added in 7.6-cm increments on 20 March and 24 April, while the plants grown under the "normal " irrigation schedule received 22.8 cm of irrigation water added in 7.6-cm increments on 20 March, 3 April, and 24 April. Control plants were grown dryland. Plant water potential, osmotic potential, stomatal resistance, and leaf temperature were monitored monthly in the spring on plants under the three watering regimes to quantify plant water stress. Yields were highest for the modified treatment (average yield: 4470 kg/ha) and were 23 % more than yields for the plants under the normal irrigation schedule (average yield: 3640 kg/ha). Average yield of dryland plants was 1660 kg/ha. After March, plants grown under the modified treatment showed more plant water stress than plants grown under the normal irrigation treatment. Dryland plants showed more stress than irrigated plants throughout the experiment. Yield and water use efficiency were maximum when irrigation water was applied under the modified regime, which received 7.6 cm less water, than under the normal regime