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Plant Water Stress Effects on Irrigated Grain Sorghum. I. Effects on Yield¹

A field study was conducted to evaluate effects of plant water stress at different stages of growth on grain and forage yields and yield components of grain sorghum [Sorghum bicolor (L.) Moench]. Irrigated grain sorghum was subjected to various periods of plant water stress beginning at (i) early boot, (ii) heading, and (iii) grain filling. Unstressed sorghum yielded 7,410 kg grain/ ha. Stress periods of 13 to 15 days [average afternoon leaf water potentials (LWP) –15.8 to –20.3 bars] did not reduce grain yields but, 27– to 28-day stress periods (average afternoon LWP, –21.7 bars) beginning at early boot or heading stages reduced yields 27%. However, a 27-day stress period (average afternoon LWP, –22.7 bars) beginning at early grain filling reduced yields only 12%. Thirty.five and 42-day stress periods (average afternoon LWP, –22.9 and –24.0 bars), beginning at boot stage reduced yields 43 and 54%, respectively. Yield reductions from stress initiated at early boot stage resulted from both reduced seed size and seed numbers. When stress was imposed at heading or later, only seed size was reduced. Forage yields were not affected by 27- to 28-day stress periods but were reduced by stress periods imposed at early boot stage and extended for 35 or 42 days.

Key Words: Sorghum bicolor (L.) • Moench • Leaf water potentials • Drought stress

² Soil scientist and agricultural engineer, USDA, Southwestern Great Plains Res. Ctr., Bushland, TX 79012,

Received for publication March 10, 1978.