Current environmental concerns, the rising economic and environmental costs of mineral fertilizers and the need to respond to the limitations of N fertilization in organic farming motivate the search for alternative sources of N in maize cropping. Forage legumes used as winter cover crops may improve soil N fertility and offer benefits to the environment. The aim of this study was to examine the effects, in a factorial field experiment, of two sowing dates (SD) and nine different cover crop treatments (balansa clover, crimson clover, gland clover, arrowleaf clover, French serradella, yellow lupin, Italian ryegrass, a cover mixture and a weedy fallow) as a potential alternative N source in an organically managed maize crop. The experiment was conducted at Viseu (Portugal) for three years (2007/2008, 2008/2009 and 2011/12), in the same field. Results showed that maize grain yield was not influenced by cover crop species but was affected by SD and the higher dry matter (DM) aboveground biomass production was observed in early SD (6.1 t ha⁻¹). The cover crops revealed their importance in maize N uptake: yellow lupin of earlier SD had the highest N uptake (83.6 kg N ha⁻¹), but this was not significantly different from balansa clover (83.2 kg N ha⁻¹). Ryegrass was the most efficient in depleting soil mineral N but values were just significantly lower than yellow lupin.

Lupin was the least efficient, leaving more mineral N in the soil than the others cover crops, immediately before the period when the risk of leaching is high. It was concluded that, under the edaphoclimatic conditions tested, most of the tested cover crops were efficient in supplying N to maize, and balansa clover had the best performance.

当前的环境问题，矿物肥料的经济和环境成本上升以及对有机农业中氮肥的局限性作出回应的需要，促使人们在玉米种植中寻找替代氮源。用作冬季覆盖作物的饲草豆科植物可以改善土壤的氮肥，并为环境带来好处。这项研究的目的是在因子分析田间试验中研究两种播种日期（SD）和九种不同的覆盖农作物处理方法（巴兰萨三叶草，深红色三叶草，腺三叶草，箭叶三叶草，法国小拉贝，黄色羽扇豆，意大利语）的影响。黑麦草，有盖混合物和杂草休耕草）作为有机管理玉米作物中潜在的替代氮源。该实验在同一地区的Viseu（葡萄牙）进行了三年（2007 / 2008、2008 / 2009和2011/12）。^-1）。覆盖农作物显示了它们在玉米吸收氮中的重要性：早期SD的黄色羽扇豆的氮吸收量最高（83.6 kg N ha ^-1），但这与巴拉兰三叶草（83.2 kg N ha ^-1）没有显着差异。黑麦草最有效地消耗土壤矿质氮，但其值仅显着低于黄色羽扇豆。

羽扇豆效率最低，在浸出风险高的时期即将来临之前，土壤中的矿物质氮比其他作物覆盖的农作物多。得出的结论是，在测试的海温气候条件下，大多数测试的覆盖作物都能有效地向玉米供应氮，而三叶草的性能最好。