Agronomic performance of soybean according to stages of development and levels of defoliation

Abstract

Insect pests have led to decreases in grain yield; yet this occurrence depends on the level of defoliation and the reproductive stage of the plant when defoliation occurs. Thus, the aim of this study was to evaluate the agronomic performance of the cultivar BRS Favorita RR® according to the stages of reproductive development of the plant at defoliation and the levels of defoliation. A randomized block experimental design was used in a 6 × 3 + 1 factorial arrangement, composed of six reproductive stages at the time of defoliation [R1 (Beginning flowering), R2 (Full flowering), R3 (Beginning pod formation), R4 (Full pod formation), R5 (Beginning seed filling), R6 (Full seed filling -100% pod filling), and three levels of defoliation (33, 66 and 99%), as well as one additional treatment without defoliation, with three replications. The following features were evaluated: Plant height, number of pods per plant, number of grains per pod, harvest index, thousand seed weight, and grain yield. It was observed that all the levels of defoliation had a significant effect on the other variables studied, with the exception of plant height. The phenological stages at the time of defoliation had a significant effect on plant height, number of pods per plant, harvest index, and grain yield. There was a decline in grain yield with levels of defoliation as of 66%, and this decline was more significant with defoliation at the more advanced stages of the crop reproductive cycle.