Cumulative crop recovery of synthetic fertiliser nitrogen (N) over several cropping seasons (legacy effect) generally receives limited attention. The increment in crop N uptake after the first-season uptake from fertiliser can be expressed as a fraction (∆RE) of the annual N application rate. This study aims to quantify ∆RE using data from nine long-term experiments (LTEs). As such, ∆RE is the difference between first season (RE^1st) and long-term (RE^LT) recovery of synthetic fertiliser N. In this study, RE^1st was assessed either by the ¹⁵N isotope method or by a zero-N subplot freshly superimposed on a long-term fertilised LTE treatment plot. RE^LT was calculated by comparing N uptake in the total aboveground crop biomass between a long-term fertilised and long-term control (zero-N) treatment. Using a mixed linear effect model, the effects of climate, crop type, experiment duration, average N rate, and soil clay content on ∆RE were evaluated. Because the experimental setup required for the calculation of ∆RE is relatively rare, only nine suitable LTEs were found. Across these nine LTEs in Europe and North America, the mean ∆RE was 24.4% (±12.0%, 95% CI) of annual N application, with higher values for winter wheat than for maize. This result shows that fertiliser-N retained in the soil and stubble may contribute substantially to crop N uptake in subsequent years. Our results suggest that an initial recovery of 43.8% (±11%, 95% CI) of N application may increase to around 66.0% (±15%, 95% CI) on average over time. Furthermore, we found that ∆RE was not clearly related to long-term changes in topsoil total N stock. Our findings show that the—often used—first-year recovery of synthetic fertiliser N application does not express the full effect of fertiliser application on crop nutrition. The fertiliser contribution to soil N supply should be accounted for when exploring future scenarios on N cycling, including crop N requirements and N balance schemes.

中文翻译：

---

合成氮肥的遗留效应

几个种植季节合成肥料氮 (N) 的累积作物回收率（遗留效应）通常受到的关注有限。第一季肥料吸收后作物氮吸收的增量可以表示为年施氮量的分数（ΔRE）。本研究旨在使用九项长期实验 (LTE) 的数据来量化 ΔRE。因此，ΔRE 是第一季 (RE ^1st ) 和长期 (RE ^LT ) 合成肥料 N 回收率之间的差异。在本研究中，RE ^1st通过15 N 同位素方法或零 N评估新叠加在长期 LTE 处理地块上的子图。RE ^LT通过比较长期施肥和长期对照（零氮）处理之间地上作物总生物量的氮吸收来计算。使用混合线性效应模型，评估了气候、作物类型、实验持续时间、平均施氮量和土壤粘土含量对 ΔRE 的影响。由于计算 ΔRE 所需的实验装置相对较少，因此仅找到了 9 个合适的 LTE。在欧洲和北美的这九个 LTE 中，平均 ΔRE 为年度施氮量的 24.4%（±12.0%，95% CI），其中冬小麦的值高于玉米。这一结果表明，保留在土壤和残茬中的肥料氮可能对随后几年作物的氮吸收做出重大贡献。我们的结果表明，施氮的初始回收率 43.8%（±11%，95% CI）可能会增加到 66.0%（±15%，95% CI）左右。随着时间的推移平均为 95% CI）。此外，我们发现 ΔRE 与表土总氮库的长期变化没有明显的相关性。我们的研究结果表明，通常使用的合成肥料氮施用第一年恢复并不能完全体现化肥施用对作物营养的影响。在探索未来氮循环情景（包括作物氮需求和氮平衡方案）时，应考虑肥料对土壤氮供应的贡献。