Effect of Pod Number on Dry Matter and Nitrogen Accumulation and Distribution in Soybean1

Abstract

Greenhouse and field studies were undertaken to document the effects of a decreased pod number on dry matter and N accumulation and distribution during grain filling in soybean [Glycine max (L.) Merr.]. Removal of about 40% of the pods significantly shifted dry matter partitioning in favor of vegetative tissues. Total dry matter and N accumulation were not affected, indicating that partial depodding did not cause feedback inhibition of photosynthesis. The crop compensated for the lower pod number with an increased 100‐ seed weight, so that final grain yield was depressed only 7 to 14% below controls.Vegetative tissue N of control field‐grown plants decreased rapidly during grain filling, and the majority of this loss was attributed to redistribution of N to the growing seed. Partial depodding greatly decreased vegetative N loss, and stem N concentrations actually increased toward the end of grain filling. Apparently, current N2 fixation roughly equalled N demand by the seed in these plants so that little net redistribution occurred. The decreased pod load may also have made more photosynthate available to support greater late‐season N assimilation than occurred in the controls.