Yield Reduction from Defoliation and Plant Cutoff of Determinate and Semideterminate Soybean1

Abstract

AbstractResearch has been conducted on the response of determinate and indeterminate soybean [Glycine max(L.) Merr.] to various plant‐damage treatments, but information is limited on the response of genotypes with a semideterminate growth habit. Our objective was to determine the yield response of a determinate cv., Forrest, and a semideterminate strain, R74‐334, to different levels of defoliation and plant cutoff at two growth stages. Treatments consisted of plants being cut off at half height, cut off at half height and defoliated below the cut, or completely defoliated. The treatments were applied to 25, 50, 75, or 100% of the plants at growth stages V5 and R3. These field experiments were conducted on a Captina silt loam (fine‐silty, mixed, mesic Typic Fragiudult) during two growing seasons. Mean yields of Forrest were significantly higher than those of R74‐334 during both years. Most of the treatments at V5 did not significantly decrease yield and in three treatments significantly increased yield. Yields generally were significantly reduced at R3 by treatments involving 50% or greater plant damage. The greatest reduction in yield occurred when 100% of the plants were cut off at half height and then completely defoliated. Yield of Forrest was reduced by 51% and that of R74‐334 by 44% with this treatment. The yield of both genotypes was reduced 33% by 100% defoliaton at stage R3. None of the first order interactions involving genotypes was statistically significant, which indicates that the two genotypes responded similarly to these plant‐damage treatments. Although there was some variability in the response of the genotypes to certain treatments, the data indicate that determinate and semideterminate soybean recover about the same from plant cutoff and/or defoliation. Therefore, the same loss values that have been developed for determinate soybean probably should be used for semideterminate types.