LAUSR

Abstract 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.