Defoliation Levels Supported in Soybean Crop With No Harm on Productivity in the Municipality of Parauapebas

Abstract

The reduction in the leaf area is one of the causes in the fall in soybean (Glycine max) productivity as it depends on the production of photoassimilates generated by the leaves, so any factor that interferes in its leaf area may affect the production. The attack of defoliating insects is among such factors. They cause a marked drop in grain yield due to its direct action, therefore, reducing the leaf area, consequently reducing the photosynthetic rate of the plant. The agronomic characteristics of the cultivars may interfere on the level of tolerance of the plant to this type of stress. The objective of this study was to evaluate the influence of defoliation levels on the vegetative and reproductive stages on the development and yield of grains in soybean cultivars. The experimental design was in randomized blocks, in a 2×11×2 factorial scheme, with four replicates. Factors consisted of defoliation stage (vegetative and reproductive), treatment levels (T1-control plant and ten treatments of artificial defoliation) and soybean cultivars (BRS 9090 RR and BRS 8890 RR). The following variables were evaluated: grain yield, dry mass of the pod, leaf dry mass, stem and root dry mass, plant height, stem diameter, number of leaves per plant, length and width of roots. It was observed that the defoliation had a negative effect on the productivity components of the cultivars, with the highest decrease in the reproductive stage, except for the treatment R5, 100% defoliation at the R5 stage, which was also reduced. In relation to the cultivars, the BRS 8890 RR was 27% better in grain yield in relation to BRS 9090 RR.

Defoliation Levels at Vegetative and Reproductive Stages of Soybean Cultivars With Different Relative Maturity Groups

“…According to Damasceno et al (2019), soybeans have a great capacity to recover from defoliation at early stages of plant development. Significant reductions in grain yield only occur when there is intense defoliation, close to 100%.…”

Impact of defoliation at the reproductive stage in different leaves of the soybean plant

“…Plants with this type of growth continue to produce new leaves even after the beginning of flowering (WERNER et al, 2016) and can reach about 70% of their final height throughout the reproductive period. Damasceno et al (2019) found no significant difference in the height of plants subjected to defoliation at different stages and levels; however, these authors observed a greater reduction in height (28% compared to the control treatment, without defoliation), when defoliation was performed at the R5 stage, but the level of defoliation in this treatment was total.…”

“…According to Damasceno et al (2019), at the early stages of development, soybean plants have a great capacity for recovery from defoliation. These authors observed no significant reductions in grain yield for defoliation carried out at the early stages of vegetative development, unless there is total defoliation.…”