The Influence of Shading, Defoliation, and Plant Population on Pod Growth and Weight in Determinate and Indeterminate Soybean Cultivars.

Pod size in soybean can be affected by a number of different factors including defoliation, light interception, and seeding rate. The objectives of this research are: 1) Examine the influence of three treatments (defoliation, shading, and seeding rate) on pod growth and weight. 2) Examine the influence of these three treatments on plant growth biomass. 3) Examine the influence of these three treatments on the relationship between plant and pod growth. Plots were established at two locations in North Carolina in 2010.  Treatments consisting of different seeding rates, shade at two periods during the reproductive stages, and manipulation of the canopy during the reproductive period. These treatments were applied to two determinate and two non-determinate cultivars.  Whole plants were harvested at regular intervals from R4 to maturity.  Biomass of the entire plant and of individual plant components (leaves, stems, pods) were measured.  The rate of increase in seed mass was compared to the rate at which plant mass increased.   The relationship between changes in seed and plant weight was used to measure stored starch, assimilate production, and the influence of environment on final seed weight. Shading reduced yield significantly; however, there was not a significant difference between the two shading dates. The seeding rate of 300,000 plants per acre had the highest yield, while defoliation and thinning resulted in the two lowest yields.