Influence of Terminal Bud Removal on the Growth and Seed Yield of Soybeans

In recent years soybean (Glycine max (L.) Merr.) yields seem to have reached an upper limit under prevailing moisture and temperature conditions using the current set of production practices. The present study was conducted to determine if changes in soybean growth resulting from removal of the terminal bud during vegetative or early reproductive stages of development would increase seed yield. The principal objectives were to determine if removal of the terminal bud of indeterminant varieties of soybeans would increase seed yields by 1) increasing the number of nodes available for pod set or 2) decreasing apical dominance. Several field experiments with treatments at different stages of development at time of bud removal, methods of removal, cultivars, seeding rates, and row widths were conducted during 2 years on Flanagan silt loam soil, a member of the fine, montmorillonite, mesic Aquic Argiudolls. Data were collected on height, lodging, maturity, number of branches, leaf area index, distribution of dry matter among pods and seeds, leaves, petioles, branches, and stems, seed yield, and 100- seed weight. Removing the apical bud increased the number of nodes on branches and decreased the number of nodes on main stems, leaving the total number of nodes unchanged. The dry weight of vegetative organs was decreased by removal of the terminal bud, but seed yields were nearly constant. Removal of the terminal bud prior to the start of flowering increased branching and lodging, reduced leaf area index, and delayed maturity slightly. When the terminal bud was removed after the start of flowering, height, leaf area index, and lodging were reduced, compared to the control. The method of bud removal (hangpinching vs. mechanical-mowing), cultivar, and planting density had little effect on growth and yield. From the data we concluded that, although the proportion of reproductive development compared to vegetative growth was increased by removal of the terminal bud, seed yields were unchanged.