Effects of source and/or sink restriction on the number of flowers, yield and dry-matter production in field-grown soybean

Source and sink organs are closely related with each other in the process of soybean yield determination. We examined the effects of source and/or sink restriction on the flowering habit, pod set and dry-matter production by removing the leaves (L), flowers (F) and/or both (L & F) from each main stem or branches at the full-flowering stage. The number of nodes increased with the removal of L or F, especially on the raceme with compound leaves. Removal of either L or F decreased the number of pods, and this extent was larger when the L or F were removed from the branches than from the main stems and when F was removed than when both L & F were removed. Removal of L or F accelerated the flowering on the non-treated main stem or branches. Removal of both L & F increased the number of flowers than removal of L or F alone. Thus, either the source or sink restriction was compensated by the increase in flower bud number. Either source or sink removal increased the pod set on the non-treated main stem or branches. Crop growth rate was decreased by removal of L or F, and this extent was larger when L or L & F were removed from the branches, but the net assimilation rate increased by the removal of L owing to the decrease in leaf area index. Pod growth rate on the branches with L removed was higher than that on the main stem with L removed, which revealed that the growth of branches was largely dependent on the assimilate from their main stem. Higher net assimilation rate in the L and L & F removed plots indicates that the surplus supply of assimilate from leaves to adjacent axil accelerates the development of flower buds considerably and promotes the pod set.