Seed yield and agronomic traits of old and modern soybean cultivars under irrigation and soil water-deficit

Abstract

An understanding of how soybean [ Glycine max (L.) Merr.] cultivars of diverse yield potential respond to soil water-deficit would be valuable to soybean breeders in planning future selections. Our objectives were to evaluate differences in seed yield and agronomic trait performance under irrigation and soil water-deficit of soybean cultivars that vary in seed-yield potential. Two older, lower-yielding (‘Manchu’ and ‘Dunfield’) and two modern, higher-yielding (‘Williams 82’ and ‘Clark 63’) cultivars were drought-stressed between first flowering and harvest maturity in 1984 and 1985 on a Flanagan (Aquic Argiudoll) silt loam soil at Urbana, Illinois. Averaged over years, seed yields of Williams 82 and Clark 63 were 31 and 9% higher than those of Manchu and Dunfield under irrigation and drought stress, respectively. Relative to the irrigated conditions, the smaller seed-yield differences between the old and modern cultivars under drought stress resulted from smaller differences in pod number per branch. The old and modern cultivars did not differ in their apparent harvest index, plant number, branch number per plant, seed number per pod, and seed weight responses to soil water treatment. Leaf-area index of Williams 82 changed the most, and Manchu the least, in relation to soil water. Leaf-area duration in the lower portion of the crop canopy was increased by drought stress to a similar extent for each cultivar, while the period of reproductive development was shortened by severe soil water-deficit more for Manchu and Dunfield than for the modern cultivars. The results of this study show greater seed-yield increases with irrigation for Williams 82 and Clark 63 than for the older cultivars which were a function of a greater number of pods and increased vegetative biomass.