Stable isotopes (e.g., ¹⁵N) can be used to develop best practices for fertilizer management in cereal crops under tropical conditions. The objectives of this study were to determine the N contribution from fertilizer and soil to wheat and corn grown in rotation and the residual N contribution from fertilizer applied to wheat and carried over to corn under Brazilian savannah conditions. This study was established in a no-till system on Rhodic Haplustox soil in a randomized complete block design with four replications. The N treatments applied to the wheat crops were 0, 20, 40, 60, 80 and 160 kg (urea-¹⁵N) ha⁻¹. The residual effects of N on the succeeding corn crop were evaluated. During the corn phase, two additional treatments were included: a control (0 N) and a treatment with 160 kg N ha⁻¹. Regression analysis showed that the highest estimated wheat yield (5415 kg ha⁻¹) was observed with the application of 114 kg N ha⁻¹. Significant effects from the residual N were observed in the corn shoot biomass and straw N uptake. On average, the recovery rate of the urea N fertilizer was 34% for wheat, and the residual urea N fertilizer use in corn (when applied to wheat) was less than 5% of the amount initially applied. The effect of the residual N was not enough to meet the N demands of the succeeding corn crop. The results of this study provide producers and the scientific community with good estimates of nitrogen use efficiency for wheat and corn.

稳定同位素（例如¹⁵ N）可用于开发热带条件下谷物作物肥料管理的最佳实践。这项研究的目的是确定肥料和土壤对轮作生长的小麦和玉米的氮素贡献，以及在巴西大草原条件下肥料对小麦的残留氮素贡献以及对玉米的残留氮素贡献。这项研究是在Rhodic Haplustox土壤上的免耕系统中进行的，随机随机完整区组设计具有四个重复。应用于小麦作物的氮处理量为0、20、40、60、80和160 kg（尿素¹⁵ N）ha ^-1。评估了氮对后续玉米作物的残留影响。在玉米阶段，还包括另外两个处理：对照（​​0 N）和160 kg N ha ^-1的处理。回归分析表明，施用114 kg N ha ^-1时，观察到最高的小麦估计产量（5415 kg ha ^-1）。在玉米茎生物量和秸秆氮吸收中观察到了残留氮的显着影响。平均而言，小麦的尿素氮肥的回收率为34％，玉米中的尿素氮素残留量（施于小麦时）少于最初施用量的5％。残留氮的影响不足以满足后续玉米作物的氮需求。这项研究的结果为生产者和科学界提供了对小麦和玉米氮素利用效率的良好估算。