Carbon and nitrogen mineralisation from green manures as alternative nitrogen sources in Mediterranean farming

The soil incorporation of green manures is a practice that can be used in sustainable agriculture and in organic farming, where nitrogen (N) sources are limited. The aim of this study was to evaluate balansa clover (Trifolium michelianum Savi), yellow lupine (Lupinus luteus L.) and ryegrass (Lolium multiflorum Lam.) as potential alternative N sources. A total of nine treatments were considered in this study: control, aerial of balansa clover, roots of balansa clover, aerial of yellow lupine, roots of yellow lupine, aerial of ryegrass, roots of ryegrass, mixture aerial + roots of yellow lupine and mixture aerial + roots of ryegrass. A laboratory incubation experiment was conducted under controlled conditions during 196 days and carbon and N mineralisation were followed. Results showed that green manures are appropriate N sources for Mediterranean farming. No significant differences in terms of N mineralisation were observed between aerial or roots biomass of the green manures. Besides, 37–55% of total N applied was mineralised in treatments amended with balansa clover or yellow lupine, whereas 13–21% of total N applied was mineralised in ryegrass. It can be concluded that the most efficient green manure for supplying mineral N to the succeeding crop was yellow lupine.