Varietal Difference in Nitrogen Redistribution from Leaves and Its Contribution to Seed Yield in Soybean

摘要

A large amount of nitrogen is redistributed from vegetative organs to the seeds during seed filling in soybean (Glycine max [L.] Merrill). However, the effect of nitrogen redistributed from leaves on the seed yield production is not clear. We evaluated the varietal difference in nitrogen redistribution and its contribution to the seed yield. Ten soybean cultivars were cultivated under conventional conditions in the field in Saga, Japan. The plant samples were collected at various reproductive stages, and then the nitrogen contents in each part were determined. The redistributed nitrogen was estimated by the difference in the nitrogen contents of leaves between the plants at the R5 and R7 stages. The nitrogen content of leaves began decreasing after R5 stage in all cultivars, indicating the start of nitrogen redistribution. About 13.8% to 37.9% of the total nitrogen in the seeds was estimated to have been redistributed from the leaf tissues in the ten cultivars. The seed yield was correlated positively with the amount of redistributed nitrogen from leaves but neither with the nitrogen concentration in the leaves at R5 nor with the proportion of redistributed nitrogen in the seeds. However, in high seed yielding years, 2008 and 2009, the seed yield was not associated with nitrogen redistribution; and the lowest nitrogen redistribution was associated with a relatively high seed yield in Tamahomare. Our results indicated that redistribution of a large amount of nitrogen does not always contribute to high seed yielding, implying the direct nitrogen uptake during seed filling could be more important factor for high seed yielding depending on the cultivars.