Analysis of the nitrogen nutrition of soybean plants with deep placement of coated urea and lime nitrogen
Tewari, Kaushal | Satō, Takanori | ABIKO, Mayumi | OHTAKE, Norikuni | SUEYOSHI, Kuni | Takahashi, Yoshihiko | NAGUMO, Yoshifumi | TUTIDA, Toru | Ohyama, Takuji
In the present study, the effect and utilization of deep placement ¹⁵N-labeled coated urea (CU) and lime nitrogen (LN) were investigated at various growth stages of soybean (Glycine max [L.]). Soybean (cv. Enrei) plants were planted in a rotated paddy field in Niigata, Japan. ¹⁵N-labeled CU or LN (100 kg N ha⁻¹) was supplied separately at a depth of 20 cm just below the seeding line. Deep placement of LN and CU significantly enhanced the dry weight and N content of the plants compared with the control treatment (Cont) without deep placement. As a result, the seed yield per plant in CU (67.2 g) and LN (70.6 g) was much higher than the Cont (37.1 g). ¹⁵N analysis of plants showed that the pattern of labeled N absorption tended to be lower with LN than CU at the R3 and R5 stages, but the recovery rate at R7 was higher in LN (70%) than CU (61%). Combining the ¹⁵N analysis with a relative ureide analysis, the N derived from nitrogen fixation (Ndfa), from fertilizer (Ndff) and from soil (Ndfs) were evaluated. At the R7 stage, the amount of Ndfa was higher in CU (32.1 g m⁻²) and LN (31.1 g m⁻²) than in Cont (21.4 g m⁻²). This positive response for N₂ fixation by the deep placement of CU and LN may result from the continuous supply of N from the lower parts of the roots, which promotes shoot growth and extends the photosynthetic activity of the green leaves, resulting in the promotion of nitrogen fixation and seed yield.
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