In a recent study, in addition to farmyard manure, cowpea was applied as green manure and faba bean as an intercrop in an organic greenhouse tomato crop, aiming to increase the levels of soil nitrogen.
Three experiments were carried out, in which legumes were either noninoculated or inoculated with rhizobia alone or together with plant growth, promoting rhizobacteria. Inoculation of legumes with rhizobia considerably increased N2 fixation in the first experiment but had no impact on N2 fixation in the second and third experiments.
In the first experiment, the application of cowpea decreased yield because it imposed a stronger nematode infection as the cowpea plants acted as a good host for Meloidogyne. However, in the second and third experiment, the nematode infection was successfully controlled and the legumes significantly increased the tomato yield when inoculated in the second experiment, irrespective of legume inoculation in the third.
The total nitrogen concentration in the tomato plant tissues was significantly increased by legume application in the second and third experiment, but not in the first. These results show that legumes applied as green manure can successfully complement nitorgen supply via farmyard manure in organic greenhouse tomato, while legume inoculation with rhizobia can increase the amounts of nitrogen provided to the crop via green manure.