EFFECT OF WATER GRADIENT ON SORGHUM GROWTH, WATER RELATIONS AND YIELD

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Abstract
A field study was conducted during the 1980 growing season to determine the effects of soil moisture gradient on sorghum water relationships, growth, and yield of 4 hybrids: S. bicolor L. ''G-623 GBR'', ''RS 626'', ''RS 671'' and ''A 28+''. June-Sept. was warmer than normal (2.3-4.8.degree. C), with precipitation of only 16.2 cm during the cropping season. Sprinklers provided a continuously decreasing moisture gradient away from the water source. Plant height, dry matter, and leaf area index (LAI) decreased as watering level decreased. Higher leaf diffusive resistance and lower water potentials were associated with decreasing plant height and decreasing LAI. Canopy temperature (Tc) of the water-stressed sorghum was generally 3.2-3.7.degree. C warmer than canopy temperatures of well-watered plants. Canopy temperature also correlated well with water use by all hybrids. The average canopy minus air temperature (.hivin.Tc-.hivin.Ta) was positive for all hybrids receiving less than 25 cm of irrigation and precipitation during the growing season, which corresponds to soil moisture values of 0.32 maximum available. Increasing the watering levels increased the water use efficiency for total dry matter and grain yield.