High nitrogen (N) fertiliser inputs together with a low N use efficiency in intensive sugarcane systems indicate substantial losses of fertiliser N to the environment and therefore the need to reconsider N fertiliser rate management. However, the effect of N fertiliser rates on the fate of fertiliser N in plant and soil, and on N fertiliser loss is largely unknown. This study established the response of ¹⁵N fertiliser recoveries to N rates on a tropical commercial sugarcane farm in Australia on a Luvisol. The experiment over 10 months included three N fertiliser rates, 150, 200 (the recommended rate) and 250 kg N ha⁻¹ applied as ¹⁵N-labelled urea (5 atom%) and a non-fertilised control. Fertiliser ¹⁵N uptake increased from 39 to 65 kg N ha⁻¹ with increasing N rates, accounting for 26% of the N applied across N rates. Fertiliser ¹⁵N contributed 22–33% to total N uptake and increased soil-N uptake compared to the control. Fertiliser ¹⁵N in the soil down to 1.0 m at harvest was consistent across N rates (36–39 kg N ha⁻¹), indicating a fixed capacity of the soil to immobilise fertiliser N. Increasing N rates did not contribute to increased sugar yield or retention of soil N but increased N fertiliser loss, ranging from 48 to 60% of the applied N. This study demonstrates that 50% of the applied N was lost from an intensive sugarcane system under current best management practices, highlighting the need to target these large environmental N losses in future recommendations.

在集约化甘蔗系统中，高氮 (N) 肥料投入以及低氮利用效率表明肥料 N 大量流失到环境中，因此需要重新考虑氮肥施用量管理。然而，施氮量对植物和土壤中氮肥的归宿以及氮肥损失的影响在很大程度上是未知的。本研究建立了澳大利亚热带商业甘蔗农场使用 Luvisol进行的^{15 次}氮肥回收率对氮肥率的响应。超过 10 个月的实验包括三种氮肥施用量，150、200（推荐施用量）和 250 kg N ha ^-1作为¹⁵ N 标记尿素（5 原子％）和未施肥对照施用。肥料¹⁵随着 N 率的增加，N 吸收量从 39 kg N ha ^-1增加到 65 kg N ha ^-1，占整个 N 率施加的 N 的 26%。与对照相比，施肥¹⁵ N 对总氮吸收和土壤氮吸收贡献了 22-33%。肥料¹⁵ N的土壤向下在收获1.0米是跨氮水平一致（36-39千克氮公顷^-1)，表明土壤固定化肥 N 的能力是固定的。增加 N 率不会增加糖产量或土壤 N 的保留，但会增加 N 肥损失，范围为施用 N 的 48% 到 60%。本研究表明在当前的最佳管理实践下，50% 的施用氮从集约化甘蔗系统中流失，突出了在未来的建议中针对这些大量环境氮流失的必要性。