Résumé
Growing winter cover crops has a great agroecological meaning, since it allow maintaining the residual inorganic N in the soil/plant system, thus avoiding leaching of N (Rodrigues et al., 2002). As winter cover crops, it can be grown diverse species (Jensen, 1992). If legume species were used, they can access atmospheric N through the establishment of a symbiotic relationship with N-fixing bacteria (Russelle, 2008). Thus, the winter leguminous cover crops can have a dual role: to uptake residual inorganic N; and promoting the growth of the following crop through a green manuring effect, which may reduce the need for expensive N fertilizers. Lupine (Lupinus albus) appears as a suitable legume species to be grown in this region, since it presents high growth rates in winter and a great ability to fix N (Rodrigues et al., 2013). In this work, the use of lupine as a winter cover crop was compared to small grains and natural vegetation (weeds) by measuring their effect on irrigated sorghum grown as a summer crop. The effect of the different winter cover crops was evaluated by comparing sorghum dry matter yield, plant N nutritional status and N recovery by sorghum plants.