Managing the nitrogen (N) supply in agroecosystems is a critical issue to ensure sufficient food production while preserving the environment. Intercropping is known to be a sustainable means of reducing the use of N-fertilizers. However, managing the N supplied to a crop while optimising the use of N by different species in a mixture remains a challenge. This is partly due to the difficulty of assessing the N requirements of each component in the mixture separately in order to correctly drive the performance of the whole system. The methods used to assess plant N nutrition status were initially developed for sole crops. In this review, i) we present different approaches adapted from these previous works to determine the N nutrition status of crops in intercrops; ii) we then compare the predictions of some of them, based on a European database of experimental results regarding cereal–grain legume and perennial grass–legume mixtures; and iii) we discuss the interests and limitations of current indices for mixed crops. We conclude that no single approach is currently valid to assess the N nutrition status of crops within the entire range of possible mixtures explored by farmers. However, some indices based on the N dilution theory perform well regarding the most common situations of balanced binary intercrops. Further research is now needed to properly address the cases of complex mixtures and severely shaded crops.

在农业生态系统中管理氮（N）的供应是一个关键问题，既要确保足够的粮食产量又要保护环境。间作是减少氮肥使用的可持续手段。然而，管理供给作物的氮同时优化混合物中不同物种对氮的利用仍然是一个挑战。这部分是由于难以分别评估混合物中每种成分的N需求以正确地驱动整个系统的性能。最初用于唯一作物的用于评估植物N营养状况的方法。在本综述中，i）我们提出了与以前的工作相适应的不同方法，以确定间作作物中的氮素营养状况；ii）然后我们比较其中一些的预测，基于欧洲关于谷物-谷物豆类和多年生草-豆类混合物的实验结果数据库；iii）我们讨论了混合作物当前指数的利益和局限性。我们得出的结论是，目前没有一种方法可以有效地评估农民探索的所有可能混合物中的作物的N营养状况。但是，基于N稀释理论的某些指标在平衡二元间作的最常见情况下表现良好。现在需要进一步研究以正确处理复杂混合物和重度遮阴作物的情况。我们得出的结论是，目前没有一种方法可以有效地评估农民探索的所有可能混合物中农作物的氮素营养状况。但是，基于N稀释理论的某些指标在平衡二元间作的最常见情况下表现良好。现在需要进一步研究以正确处理复杂混合物和重度遮阴作物的情况。我们得出的结论是，目前没有一种方法可以有效地评估农民探索的所有可能混合物中的作物的N营养状况。但是，基于N稀释理论的某些指标在平衡二元间作的最常见情况下表现良好。现在需要进一步研究，以正确解决复杂混合物和严重遮阴作物的情况。