Minimum optimal seeding rate for indeterminate soybean cultivars grown in the tropics

The minimum optimal seeding rate in soybean [Glycine max (L.) Merr.] is the least seeds required to achieve optimal yield. This is a function of the crop phenotypic plasticity in response to plant density. However, the effect of seeding rate reduction on the seed composition and yield of cultivars with contrasting branching potentials needs to be better elucidated. The objectives were to evaluate the impacts of reducing the seeding rate on production and to quantify the minimum optimal seeding rate for seed, oil, and protein yield in soybean cultivars with contrasting plant architectures. The field experiment was conducted for two growing seasons in a 5 × 2 factorial scheme in a randomized complete block design with five replications. The treatments consisted of five seeding rates (100, 80, 60, 40, and 20% of the recommended seeding rate) and two indeterminate cultivars (BRS 1010IPRO and NS 5959IPRO). Both cultivars showed a minimum optimal seeding rate below the recommended rate. Pods per m2 and the number of seeds per pod were the yield components responsible for the compensatory effect in response to lowering the seeding rate. Thousand seed weight was the main yield component responsible for yield loss below the minimum optimal seeding rate. Both cultivars showed high branch yield in response to seeding rate reduction. BRS 1010IPRO has a higher potential for seeding rate reduction than NS 5959IPRO. The minimum optimal seeding rate for seed yield in NS 5959IPRO led to lower protein yield and higher oil yield.