This study checked the nitrogen (N) uptake, fate of the N fertilizer, fertilizer recovery efficiency (FRE) and the residual amount of N fertilizer in the soil via 15N-labelled fertilizer applied to soybean (Glycine max L. Merr.), to explain any differences in the yields. Two soybean field experiments were established in Brazil, one conducted in a tropical (Trop) zone located at Cerrado Biome and the other in a subtropical (Subt) environment. The experimental design was a 2-factor in randomized complete block with four replications. Five doses of N (0, 20, 40, 80 and 120 kg ha−1) were applied at two soybean growth stages (VE and R3). For all treatments, except No-N, 15N-labelled fertilizer was used. The N uptake and the amount of N fertilizer were analysed in the roots, shoots, grains and whole plant, the FRE and yield by soybean, and the residual of fertilizer in the soil. The total N uptake (Nplant) was greater with fertilization at R3 stage compared to the other stage, and N application increased the yield just at this stage and in the Trop condition. The increase in N shoot (not specifically from fertilizer) with the application at R3 appeared to be related to the increased in yield. However, the N from fertilizer found in the plant shoot was about 20% higher when fertilizer was applied at VE compared with R3. Under Subt condition, the FRE averaging 55%. In contrast, the FRE decreased from low to high nitrogen rates (64 to 40%, respectively) when soybean grown under Trop condition. Most N from fertilizer (38%) was found in the grains, followed by the shoot (14.6%) and the root (0.58%). The use of N fertilizer at reproductive growth stages is a better approach to meet soybean N demand through N fertilization. Potential yield gains are more reliable under Trop condition.

中文翻译：

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与大豆产量相关的氮肥回收和分配

本研究通过对大豆 (Glycine max L. Merr.) 施用 15N 标记的肥料，检查了土壤中氮 (N) 的吸收、氮肥的归宿、肥料回收效率 (FRE) 和氮肥的残留量，以解释产量的任何差异。在巴西建立了两项大豆田间试验，一项在位于 Cerrado 生物群落的热带 (Trop) 区进行，另一项在亚热带 (Subt) 环境中进行。实验设计是具有四次重复的随机完整区组的 2 因子。在大豆的两个生长阶段（VE 和 R3）施用五剂 N（0、20、40、80 和 120 kg ha-1）。对于所有处理，除 No-N 外，均使用 15N 标记肥料。分析了大豆的根、芽、籽粒和整株的吸氮量和施氮量，FRE和产量，以及土壤中肥料的残留。与其他阶段相比，R3 阶段施肥的总氮吸收量（Nplant）更高，施氮增加了这一阶段和 Trop 条件下的产量。在 R3 施用时 N 芽（不是特别是来自肥料）的增加似乎与产量增加有关。然而，与 R3 相比，在 VE 施肥时，植物芽中肥料中的 N 高出约 20%。在 Subt 条件下，FRE 平均为 55%。相比之下，当大豆在 Trop 条件下生长时，FRE 从低氮到高氮（分别为 64% 到 40%）下降。来自肥料的大部分氮 (38%) 存在于谷物中，其次是芽 (14.6%) 和根 (0.58%)。在生殖生长阶段使用氮肥是通过施氮来满足大豆对氮需求的更好方法。Trop 条件下的潜在产量收益更可靠。