Cut‐Off, Break‐Over, and Defoliation Effects on a Determinate Soybean Cultivar1

Abstract

AbstractExtensive research has been conducted on the response of indeterminate soybeans [Glycine max(L.) Merr.] to different types of plant damage, but information on the effect on determinate growth types is limited. This research compared the responses of a determinate soybean cultivar to different intensities of cut‐off, break‐over, and defoliation at five stages of plant growth. The experiments were conducted on a Captina silt loam (fine silty, mixed, Typic Fragiudnlt) during 1981 and 1982 at Fayetteville, AR. Plants were cut off at the point that removed half fresh weight and defoliated below the cut, broken over at the point that divided the aboveground fresh weight in half and defoliated below the break, or completely defoliated. Treatments were applied to 33,66, or 100% of the plants at growth stages V10, R2, R3, R4, and R5. Yields generally were not reduced when 33% of the plants were treated. The cut‐off treatments generally caused greater yield reduction than break‐over or defoliation; defoliation generally caused a greater yield reduction than breakover when 66 or 100% of the plants were damaged. Yield reductions were greater when treatments were imposed at progressively later growth stages. Cut‐off and defoliation influenced seed weight and date of maturity more than break‐over, especially when all plants were treated. Seed weight was reduced when yield reductions were severe, but the loss in seed weight did not account for all the yield loss. Maturity was delayed up to 2 weeks by treatments at R2, R3, and R4, and hastened by treatments at R5.