Soybean tolerance to defoliation as affected by row spacing reduction

The row spacing reduction from 40 to 20 cm increase radiation interception, leaf area index and grain yield. This experiment aimed to evaluate if the row spacing reduction influence soybean tolerance to loss of photosynthetic area. The research was performed using no-till tillage system at the Agronomic Experimental Station of Universidade Federal do Rio Grande do Sul, during the 2000/01 growing season. Treatments were arranged in a split-split plot randomized complete block design, with four replications. Treatments included five combination of defoliation in three stages of development (V9 - ninth-node, R2 - full bloom and R5 - beginning of seed filling), two row spacings (20 and 40 cm) and four defoliation levels (0 - control, 33, 67 and 100%). The cultivar tested was FT-Abyara. Defoliations performed at the reproductive stages decrease grain yield, especially when curried at the begging of grain filling (R5). The control grain yield was 21% higher when soybean was sown with rows 20 cm apart (4134 kg ha-1) than with 40cm rows (3413 kg ha-1). Narrow rows always provided higher yields in all defoliation levels. The component that influenced yield the most was the number of pods m-2. These results indicate that row spacing reduction from 40 cm to 20 cm is a positive management strategy for soybean production regardless of defoliation level. (author)