Sustainable management of nitrogen nutrition in winter wheat through temporary intercropping with legumes

Wheat-legume temporary intercropping with legume devitalization in late winter can increase the N self-sufficiency of cropping systems and improve the N nutrition of wheat as a cash crop. However, this practice has been scarcely investigated. In this study, carried out in a Mediterranean environment with cold winters, we compared 14 treatments over 3 years with different weather patterns: (A) pure stands of common wheat (Triticum aestivum L.) grown at 0, 40, 80, 120, 160 kg N ha(-1); (B) pure stands of faba bean (Vicia faba L. minor), pea (Pisum sativum L.), and squarrose clover (Trifolium squarrosum L.); (C) temporary intercrops of wheat and faba bean, pea, or clover; and (D) permanent intercrops of wheat and the same legumes. In the temporary intercrops, all legumes improved the wheat N availability compared with the unfertilized control. The "N effect" of legumes for wheat was consistent across years and proportional to the competitive ability of the legumes, i.e., faba bean > pea > clover. The higher the legume competitive ability, the higher was its N accumulation before devitalization, and the higher/earlier was the N supplied to wheat. Our findings demonstrate that the date of legume devitalization represents a key factor to be managed each year in order to maximize legume N supply while preventing excessive legume competition, which could undermine wheat growth and yield. Such a modulation was not possible in permanent intercrops, where legume competition depressed wheat grain yield. The N supplied with legume devitalization increased wheat grain N accumulation during grain filling. This is the first work comparing temporary and permanent intercrops of wheat with different legumes and over different seasons. Overall, temporary intercropping appears to be a feasible and efficient tool for the sustainable management of N nutrition in winter wheat.