Effect of Soil Water Stress at Various Growth Stages on Soybean Yield1

Abstract Conventional irrigation experiments and rainfall distribution‐yield studies have indicated that insufficient water during flowering and pod‐fill stages frequently limits yields of soybeans (Glycine max (L.) Merr.). In this 3‐year experiment, field plot covers were used to control rainfall and water stress was imposed on plants at various stages of growth to determine more specifically the critical periods for irrigating soybeans for maximum yields. Soil water regimes ranged from a limited supply (10% available soil water) to adequate water (50% available) during the entire growing season. More bean production was obtained from water applied after full bloom than earlier. The pod‐fill stage, from August 15 to September 20 for ‘Bragg’ soybeans at Thorsby, Alabama, was the critical time for adequate water for maximum yields. Yields from adequately watered soybeans were 540 to 1,040 kg/ha, or 24 to 55%, greater than where water was limited throughout the growing season. Highest yield obtained under the best water regime was 3,320 kg/ha. Conditions limiting yields were not obvious.