Demand and supply of N in seed production of soybean (Glycine max) at different N fertilization levels after flowering |
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Authors: | Toshihiko Kinugasa Takashi Sato Shimpei Oikawa Tadaki Hirose |
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Affiliation: | (1) Faculty of Agriculture, Tottori University, 4-101 Koyama-Minami, Tottori 680-8553, Japan;(2) Faculty of Bioresource Sciences, Akita Prefectural University, Akita 010-0195, Japan;(3) Department of International Agricultural Development, Tokyo University of Agriculture, Tokyo 156-8502, Japan |
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Abstract: | Nitrogen (N) has been suggested as a determinant of seed production especially in species with high seed N content. Assuming that seed yield was determined as the balance between N demand and supply for seed production, we studied the effect of N fertilization after flowering on soybean (Glycine max L. Merr.) yield. Seed N concentration was nearly constant irrespective of N fertilization, indicating that seed production was proportional to the amount of N available for seed growth. N demand for seed production was analyzed as the product of seed number, the rate of N filling in individual seeds, and the length of the reproductive period. N fertilization increased seed number and the reproductive period, but did not influence the N filling rate. Seed number was positively correlated with dry mass productivity after flowering. Three N sources were distinguished: mineral N uptake, symbiotic N2 fixation and N remobilization from vegetative body. N fertilization increased N uptake and N remobilization, but lowered N2 fixation. We concluded that N availability in the reproductive period determined seed yield directly through increasing N supply for seed growth and indirectly through increasing seed N demand with enhanced plant dry mass productivity. |
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