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 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.