Effect of Plant Spacing Within a Row on the Competitive Ability of Soybean Genotypes

Abstract

Intra‐row intergenotypic competition among two sets of three soybeans (Glycine max L. Merrill) genotypes were compared in pure stands and in mixtures using 10‐, 20‐, 41‐, and 81‐cm spacings between plants. Differences among genotypes for plant height and maturity were considerably greater in set I than in set 2. Competition effects were less for set I under the unfavorable enviromnent of 1964 and greater under the more favorable environment of 1965, while the reverse occurred for set 2. In both years, competition effects in set 1 were mostly additive. In set 2, competition effects were non‐additive in 1964, a decrease in yield, height, number of branches, nodes and pods per plant occurring in mixtures as compared with pure stands. In 1965, competition effects were additive for most characters except seed weight and seeds per pod, where the non‐additive effects were positive and negative, respectively. The magnitude of competition effects at different spacings was somewhat erratic. In general, competition effect increased as the distance between plants decreased in set 2. In set 1, competition effect increased as plant spacing increased from 5 to 20 cm in 1964 and from 5 to l0 cm in 1965; thereafter it decreased. At the 81 cm spacing no competition effect occurred for yield.