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Moisture Deficits and Grain Sorghum Performance: Effect of Genotype and Limited Irrigation Strategy¹

The response of three selected sorghum [Sorghum bicolor (L.) Moench] hybrids to a wide range of timings and intensities of drought stress were studied in field experiments on a sandy soil (Typic Ustipsament) in west central Nebraska. A modified line source sprinkler irrigation gradient was used to create the treatments.

Yield reductions (41 to 45%) resulting from the gradual intensification of stress over the entire season were large but very similar among genotypes. Greater genotypic differences occurred in treatments in which irrigation was limited during only one or two growth periods

The genotypic rankings for yield were quite consistent over the range of treatments, with the hybrid of highest yield potential (RS 626) usually continuing to demonstrate superior yields under drought stress. The hybrid (NB 505) of lowest yield potential did not show a comparatively greater drought resistance (i.e., a lower percentage yield reduction) under severe stress.

Grain yield tended to be linearly related to seasonal net water application and to variations in the percent of the soil water deficit that was replaced each week, regardless of variety or the growth stage(s) at which irrigation was limited.

The timing of irrigation was quite critical with large differences in the response of each hybrid to the same quantity of seasonal water applied under varying strategies. The data for both years and all genotypes indicated that an optimal strategy for allocating water under limited irrigation would be to apply a constant fraction of the crop's maximum water usage each week, allowing stress to gradually and progressively intensify throughout the season. Yield reductions will occur but these will tend to be lower per unit of irrigation water saved than when irrigation is limited only in individual growth periods.

Key Words: Sorghum bicolor (L.) Moench • Drought resistance • Water management

² Graduate research assistant (Presently res. associate, Agronomy Dep. Int. Rice Resch. Inst.); Professor Agric. Engr.; plant physiologist, USDA-ARS and professor agric. engr., Univ. of Nebraska, Lincoln.

Received for publication August 7, 1981.