Quantifying the fate of nitrogen (N) fertilizer is essential to develop more sustainable agricultural N management practices. However, our understanding of N losses, particularly in low fertility soils remains incomplete. We evaluated the fate and N use efficiency of N fertilizer under different long-term fertilization regimes, i.e., no N; synthetic N; manure plus synthetic N in a calcareous Cambisol in the North China Plain. A standard rate (160 kg N ha⁻¹) of ¹⁵ N-labelled urea was applied to the above treatments in summer maize (first crop) and the same amount of unlabelled urea was applied to winter wheat (second crop). We found the manure plus synthetic N treatment had a significantly higher fertilizer N use efficiency (56%) with lower residual fertilizer N in soil (47 kg N ha⁻¹) than the synthetic N treatment (46% and 64 kg N ha⁻¹_, respectively), due to the better synchrony of fertilizer N supply and crop demand in the manure plus synthetic N treatment. Surprisingly, compared with the synthetic N treatment, application of N fertilizer to the N-deficient treatment increased fertilizer N use efficiency significantly to 68%, and reduced the residual fertilizer N in soil (31 kg N ha⁻¹). Fertilizer N losses accounted for 11–16% of applied ¹⁵N-labelled urea with no significant differences between treatments. We found that fertilizer N use efficiency was increased in the high fertility soil supplied with manure compared with the low fertility soil supplied with synthetic N fertilizer, which emphasized the importance of recycling the manure or crop residues to soil.

量化氮 (N) 肥料的归宿对于开发更可持续的农业氮管理实践至关重要。然而，我们对氮损失的理解仍然不完整，特别是在低肥力土壤中。我们评估了不同长期施肥制度下氮肥的归宿和氮利用效率，即不施氮；合成氮；华北平原钙质 Cambisol 中的粪肥加合成 N。将标准比例（160 kg N ha ^-1）的¹⁵  N 标记尿素施用于夏玉米（第一季）的上述处理，并将相同量的未标记尿素施用于冬小麦（第二季）。我们发现粪肥加合成氮处理具有显着更高的氮肥利用率 (56%)，土壤中残留的氮肥 (47 kg N ha)^-1）比合成N处理（46％和64公斤氮公顷^-1 _，分别地），由于在粪便加合成N处理肥料氮供应和需求作物的更好同步。令人惊讶的是，与合成氮处理相比，在缺氮处理中施氮肥显着提高了肥料氮的利用率，达到了 68%，并减少了土壤中的残留肥料 N（31 kg N ha ^-1）。肥料氮损失占施用量的 11-16% ¹⁵N-标记的尿素在处理之间没有显着差异。我们发现，与施用合成氮肥的低肥力土壤相比，施用有机肥的高肥力土壤的肥料氮利用效率提高，这强调了将粪肥或作物残留物回收到土壤中的重要性。