Nitrogen (N) is crucial for crop production. Crop sequences with different legume participation affect N availability and therefore N fertiliser management. The study aimed to assess the inclusion of winter crops (WC) with different amounts of residues and different C:N ratios on the following: (i) the response to N fertilisation in the following late‐maize (Zea mays L.), and to carry that comparison into a subsequent wheat crop (Triticum aestivum L.), and (ii) identify soil N indicators associated with these responses. Two field experiments (E1 and E2) were conducted in the Argentinean Pampas during two growing seasons to evaluate a WC/late‐maize‐wheat sequence under no‐tillage. In each experiment, late‐maize was sown after a bare‐fallow and three WC: wheat, vetch (Vicia villosa L.) and field pea (Pisum sativum L.), where five rates of N fertilisation were evaluated. An area of late‐maize that was not fertilised with N within each previous WC was used to evaluate the response to N fertilisation in the subsequent wheat crop. Indigenous N was estimated by using N uptake in the non‐N‐fertilised treatments. Soil N indicators and C:N ratio of WC residues were evaluated as indicators of response to N fertilisation in both crops. Significant responses to N fertilisation in grain yield and N uptake were observed in late‐maize when bare‐fallow and wheat were the previous treatments in both experiments. In contrast, vetch and field pea supplied 32 and 40 kg N ha−1 in E1 and E2, respectively, and showed no response to N fertilisation, satisfying the N required by late‐maize. However, this supply was not enough to sustain the N demand of the subsequent wheat, where the response to N addition ranged from 36% to 74% when vetch and wheat were the previous WC, respectively. Only soil inorganic N indicators were associated with indigenous N supply. Moreover, the apparent net WC effect was linked to late‐maize (r2 = 0.91) and subsequent wheat (r2 = 0.67) grain yield response, which was also related to the C:N ratio of the WC residues in late‐maize and the subsequent wheat (r2 = 0.78), suggesting that mineralisation occurs when C:N ratio is below 18. Consequently, in future studies the C:N ratio of the WC residues can be included in N fertilisation recommendation schemes when late‐maize is sown as a double crop in more intensified crop sequences.

中文翻译：

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作物氮胁迫缓解——一种分析晚玉米-小麦序列中冬季作物残留氮的系统方法


氮 (N) 对于作物生产至关重要。不同豆科植物参与的作物序列会影响氮肥的利用率，从而影响氮肥管理。该研究旨在评估具有不同残留量和不同碳氮比的冬季作物 (WC) 的以下方面：(i) 晚熟玉米 (Zea mays L.) 对施氮肥的反应，以及将这种比较与随后的小麦作物（Triticum aestivum L.）进行比较，并且（ii）确定与这些反应相关的土壤氮指标。在阿根廷潘帕斯草原的两个生长季节进行了两次田间试验（E1 和 E2），以评估免耕条件下的 WC/晚熟玉米-小麦序列。在每个实验中，晚玉米在裸休和三个休耕后播种：小麦、野豌豆 (Vicia villosa L.) 和豌豆 (Pisum sativum L.)，其中评估了五种氮肥施肥率。使用在之前的每个WC中未施氮肥的晚熟玉米区域来评估随后的小麦作物对施氮肥的反应。本地氮是通过使用非施氮处理中的氮吸收来估计的。土壤氮指标和WC残留物的碳氮比被评估为两种作物对施氮肥的反应指标。在两个实验中，当裸休和小麦为先前处理时，晚玉米中观察到氮肥对谷物产量和氮吸收的显着反应。相比之下，野豌豆和豌豆在E1和E2中分别提供了32和40 kg N ha−1，并且对施氮肥没有反应，满足晚玉米所需的氮。然而，这种供应不足以维持后续小麦的氮需求，当野豌豆和小麦作为前一个WC时，对氮添加的反应分别为36%至74%。 只有土壤无机氮指标与本地氮供应相关。此外，明显的净WC效应与晚熟玉米（r2 = 0.91）和晚熟小麦（r2 = 0.67）籽粒产量响应相关，这也与晚熟玉米和晚熟小麦中W​​C残留物的C:N比率有关。晚小麦（r2 = 0.78），表明当 C:N 比率低于 18 时发生矿化。因此，在未来的研究中，当晚玉米播种时，WC 残留物的 C:N 比率可以纳入氮施肥建议方案中更密集的作物序列中的双作物。