Studies on the dynamic status of nitrogen and carbon, and their efficient utilization in crop production

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This study is an attempt to elucidate the dynamic status of mitrogen circulating between plants and soil and carbon closely related with mitrogen metabolism in the plants for gramineous crops, leguminous crops and vegetable crops. The results obtained from rice study were summarized as follows:1. Nirogen circulation in rice plants grown in paddy fields: Nitrogen-use efficiency varied among varieties. It was recognized that ^<15>N with high atom% should be used for monitoring residual fertilizer N in soil.2. Up-take and translocation of nitrogen applied at different growth stages in rice plants: Earlier topdressing produced greater top dry weights and smaller grain yields. Nitrogen-use efficiency varied among varieties, with higher efficiencies in later topdressing.3. Effects of character of rice seedlings on nitrogen circulation in rice plants immediately after transplanting: Rice plants with different characters during the nursery period varied in nitrogen up-take and the re-translocation of nitrogen from leaf and stem to root after transplanting.4. Circulation of nitrogen and carbon in rice seedlings at rooting stage: After transplanting, nitrogen and carbon are translocated from the lower leaf blades and leaf sheath to the upper ones.5. Nitrogen-use efficiency of rice plants in different rooting zones: Nitrogen-use efficiency of rice plants was higher in the larger rooting zones. The nitrogen-use efficiency at the times of heading and maturity was higher in base dressing than in topdressing.6. Intra-hill interaction of different rice cultivars on ^<15>N allocation: In the companion planting of two cultivars differing in plant type, nitrogen absorption rate varied among rooting-zone sizes. Ten studies on gramineous and leguminous crops and vegetable crops other than rice plants were conducted during four years.