Soybean Recovery from Plant Cutoff, Breakover, and Defoliation¹

Abstract

The current procedure for assessment of hail injury to soybeans (Glycine max (L.) Merr.) assumes that plant cutoff, breakover, and defoliation cause equivalent percentages of yield loss. Our objective was to compare the yield response of soybeans to the three types of injury in field experiments. Plants were cut off at half height and defoliated below the cut, broken over at half height and defoliated below the break, or completely defoliated. The treatments were applied to 33, 66, or 100% of the plants at the V5, R2, R3, R4, and R5 stages of development at one location in Iowa and at the R2 to R5 stages at one location in Minnesota during 1981. Yield losses from the three types of injury were not the same. Removal of the top half of the main stem by the cut‐off treatment was generally more severe than breaking it over or removing the leaves, especially when 100% of the plants were treated at later stages of development. At V5 and R2, breakover tended to cause greater yield loss than defoliation; at R3, the two treatments were the same; and at R4 and R5, defoliation caused greater yield loss than breakover. Reduction in seed weight and changes in time of maturity were generally small, except when 100% of the plants were treated. The treatments did not cause changes in lodging scores of practical importance when brokenover plants were ignored. Small reductions in plant height were observed for breakover and defoliation, but substantial reductions were observed for cutoff. The three types of plant injury should be considered independently in assessing damage caused by hail.

Yield Response to Early Defoliation in Spring‐Planted Canola

“…Fully defoliating plots at the two-leaf stage resulted in the crop yielding 86% of the control, while a similar level of defoliation at the ten-leaf stage resulted in seed yield of 66% of the control. Other crops, such as lentil (Lens culinaris L.), soybean, and sunflower (Helianthus annuus L.), have shown more consistent relationships between levels of yield loss and defoliation timing (Fehr et al, 1983;Schneiter et al, 1987;Muro et al, 2001;Bueckert, 2011); however, in the noted studies the defoliation occurred primarily during the reproductive phase of crop growth. At the 2011 Nasser site, partially defoliated plots trended toward overyielding with progressively later timings, while fully defoliated plots yielded similarly regardless of timing (Table 3; Fig.…”

“…The variable response of canola yield to defoliation timing among sites was unexpected based on results from other crops and did not support our hypothesis that later defoliation timings would necessarily result in greater yield loss. Other crops, such as lentil (Lens culinaris L.), soybean, and sunflower (Helianthus annuus L.), have shown more consistent relationships between levels of yield loss and defoliation timing (Fehr et al, 1983;Schneiter et al, 1987;Muro et al, 2001;Bueckert, 2011); however, in the noted studies the defoliation occurred primarily during the reproductive phase of crop growth.…”

Plant Density and Defoliation Effects on the Recovery of Soybean Injured by Stem Cutoff During Vegetative Development

“…The effect of defoliation on plants injured by stem cutoff during vegetative development is not as well understood. During vegetative development, removing a portion of the main stem decreases seed yield, but defoliation at the same stage of development has no significant effect on seed yield (Fehr et al, 1983). The adjustment procedures currently in use assume that yield reductions caused by stem cutoff with and without defoliation are not significantly different.…”

Resposta da cultura da soja a diferentes intensidades de injúria nos estágios iniciais de desenvolvimento

“…Yield reductions associated with plant injury tend to be greater during reproductive than during vegetative development stages (WEBER, 1955;FEHR et al, 1983;CONLEY et al, 2008). The stage considered the most critical for soybean plants ranges from R3 to R6, a phase in which the plants need the highest production of photoassimilates (TURNIPSEED, 1972: GAZZONI & MINOR, 1979GAZZONI & MOSCARDI, 1998;HAILE et al, 1998;RIBEIRO & COSTA, 2000).…”