EFFECTS OF PLANT POPULATION AND FERTILIZER ON THE GROWTH AND YIELD OF SOYBEANS

Abstract

High-density (32 plants/m2) planting of soybeans [Glycine max (L.) Merrill] resulted in small plants but high dry weights per unit area of ground, while low density (four plants/m2) produced larger plants with a smaller dry weight per unit area of ground. Intermediate densities (16 and 8 plants/m2) produced intermediate plant sizes and yields. Shoot/root, bean/shoot, and leaf area ratio were all decreased by increasing density. The effects of density on plant growth were detectable 30 to 40 days from planting, and increased rapidly thereafter.Fertilizer in moderate quantity depressed the growth of the whole plant in the early stages, but, by maturity, fertilizer was associated with a small increase in weight of shoot and an increase in the proportion of beans to shoot.High density reduced the proportion of flowers forming mature pods, while fertilizer application increased it.There was no interaction between fertilizer level and density of planting on any plant characteristic.Effects of fertilizer on later stages of growth could be attributed mostly to N; effects on early stages of growth are more difficult to interpret but suggest an extreme sensitivity to fertilizer, which may be involved in the generally observed poor response of soybeans to fertilizer.