Screening of legumes as cover crops: nitrogen and weeds

This study evaluated 27 legumes as cover crops, sowed in pure or mixed stands, with the aim to outline their agrosystemic services. The results show important behavior variations among the different legumes. The amount of aerial biomass built from August until the first frost achieve between 0.4 and 5.9 t DM/ha. From 377 to 850 degrees-days are necessary to reach 50 % of soil cover. The nitrogen accumulated by the legumes is mainly due to symbiotic nitrogen fixation and vary from a few kg to 150 kg N/ha. The ability of legumes to compete with weeds is closely correlated with the amount of biomass produced (R2 = 0.93). It is analogous to the aptitude of association tested on legumes in mixtures with oat and phacelia. Five species (grass pea, faba bean, hairy vetch, common vetch and pea) are found to be very dominant and reach more than 80 % of biomass in mixture with phacelia and about 70 % with oat. These species are also those producing the highest biomass, covering soil most rapidly, and fixing high quantity of nitrogen. Many other legumes (fenugreek, lentil, white lupin, soybean, berseem clover, persian clover, crimson clover, hungarian vetch) show less competitive performance and offer a good complement for species associations.