Effects of artificial defoliation in grain yield and its components in two soybean cultivars

Abstract

A field experiment was conducted during the 1978/1979 growing season at the Agronomic Experimental Station, UFRGS, Guaíba, with the objective of determining the effects of defoliation levels of 33, 67 and 100%, applied at the development stages V4, R1/R2, R3, R4, R5 and R6 in two soybean cultivars, Paraná (early maturity) and Santa Rosa (late maturity). Defoliation levels had different effects upon plant development according to the development stage. For the late cultivar, V4 was the least critical stage, and R1/R2 for the early one, defoliation even resulted in a yield increase in the short season cultivar. The greastest decrease in yield was found when defoliation was performed at R5, for both cultivars. The adverse effects increased with higher levels of defoliation. The components determining yield reduction were pods per plant for the early cultivar and seeds per plant for the full season cultivar.