Response of Glycine max L. to organic matter based on Tithonia diversifolia (HEMSL.) A. Gray on a ferralsol in Mbuji-Mayi/DRC

The soil used for our investigations is a ferralsol, extremely acidic, poor in nitrogen and moderately supplied with available phosphorus. In this highly degraded soil, the exclusive use of chemical fertilisers is not feasible, not only because of their negative impacts on the soil and the environment, but also because of their high cost. Thus, other alternatives that are less aggressive on the soil should be sought. Here, the use of organic matter (OM) based on Tithonia diversifolia was proposed as a possible solution to restore the fertility of this type of soil. The general objective was to evaluate its impact on the cultivation of soybeans sown in vegetation pots on two substrates, from the superficial layer (0-20 cm) and the deep layer (20-40 cm) in a two-factor experimental set-up. Three doses, equivalent to 0 kg (D0), 3 kg (D1) and 6 kg MO.m-2 (D2) were tested. According to the results obtained, the 3 kg MO.m-2 treatment, equivalent to 30 Mg.ha-1, was the best in all cases, particularly with regard to yield, which was equivalent to 3.72 Mg.ha-1 on the surface soil and 3.48 Mg.ha-1 on the deep soil. These results are far superior to those generally obtained in various trials across the country. The control, 0 kg OM, which had only a few nodules (8), gave a yield of only 0.486 Mg.ha-1. This proves that Rhizobium activity and development are inhibited in this soil and allows us to say that it is illusory to rely on symbiotic nitrogen fixation for the plant's needs. With the 6 kg OM.m-2 dose, a drop in yield was observed (1.642 Mg.ha-1 on average), probably due to excess nitrogen. However, in general, the soils of both layers (0-20 cm) and (20-40 cm) behaved almost the same.