Plant water stress at various growth stages and growth and yield of soybeans

In the Southern High Plains of the U.S.A., where water for irrigation is being depleted, drought-tolerant crops are extensively grown under limited irrigation where less water is applied than is required for potential evapotranspiration and maximum yield. This study was conducted (1) to determine the effects of plant water stress at various growth stages on growth and yield of soybeans [Glycine max (L.) Merr.] and (2) to assess the adaptability of the soybean plant to limited irrigation in the stressful climate of the Southern High Plains. The 3-year study was conducted on Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll). Soybeans ('Douglas', indeterminate, maturity group IV) were grown with different irrigation treatments designed to subject the plants to water deficits at different growth stages. Stress initiated during R1 (early flowering) or R2 (full bloom) and extending to R3 (beginning pod development) reduced seed yields by 9-13%. But, when stress was extended to R4.5, yields were reduced by 46%. Stress beginning at R3 and extending to R4.5 reduced yields by 19%. Stress imposed at R5 and relieved at R6 reduced yields 15% in one year and 46% in a more stressful year. Stress imposed at R5 and extending to the end of the growing period (5 weeks) reduced yields by 45% in the less-stressful year and by 88% in the other. Stress throughout the last 3 weeks of the growing period (beginning at R6) reduced yields by 21 and 65%, respectively, in the two years. Water-use efficiency was not increased under limited irrigation. Soybeans are amenable to limited irrigation under the stressful climate of the Southern High Plains, but their vulnerability to drought stress during seed development complicates management. They are more suited for limited irrigation than is corn (Zea mays L.) but are less suited than are grain sorghum [Sorghum bicolor (L.) Moench], cotton (Gossypium hirsutum L.) or wheat (Triticum aestivum L.).