We implemented complete randomised block designs over a 3-year rotation in two farm sites of southern France to test the non-crop legume Crotalaria juncea for biological control of phytoparasitic root-knot nematode populations and green manure effect in greenhouse tunnel vegetable production (lettuce) suffering from recurrent and severe nematode infestation problems. Crotalaria intercrop cultivation was introduced as an alternative cover plant to Sorghum. Crotalaria plants were inoculated at sowing with a cocktail of rhizobium strains, grown for 60-65 days, cut and the residues incorporated into soil; lettuces were then planted and harvested after 75-day growth. Several parameters were measured: Crotalaria plant growth, root nodulation, 15N natural abundance, N concentration and percentage of N2 fixed in C. juncea; subsequent lettuce crop yield and nematode infestation (galls); microbiological impact of Crotalaria in soil and roots. Soil samples were analysed for Corg-N-P contents, DNA extraction to monitor bacterial diversity, estimation of microbial catabolic potentialities (substrate induced respiration) and trap cultures of mycorrhizas. Statistical analyses show that C. juncea (1) grows rapidly in Mediterranean conditions producing a significant biomass (2) has a very positive green manure effect on lettuce production in both sites and within two successive campaigns (3) significantly reduce on lettuce gall scores. Mycorrhization index and rate of C. juncea are significantly higher than that of Ray-grass used as a reference mycorrhizogenous plant. Bacterial strains recovered from nodules show a larger diversity than that of the inoculated strains. One of the inoculated Bradyrhizobium sp. strain was still present in soil one year after inoculation. Measurements of natural abundance in 15N show that the proportion of nitrogen fixed is quite low over the whole plot (Ndfa=15%) although it varies a lot between blocks (from 3 to 30%). Nevertheless, this corresponds to