Sustainable improvement of soil biogeochemical performance and physical fertility in semiarid tropics by using indigenous N2-fixing cyanobacteria

The study was aimed to establish a realistic innovative approach, for promoting a sustainable increase of overall soil fertility of marginal lands in representative semiarid environments in East and Southern Africa (South Africa, Tanzania and Zimbabwe) by application of indigenous selected strains of soil cyanobacteria fixing atmospheric Nitrogen, and releasing organic compounds (i.e. exopolysaccharides, EPS) able to improve soil fertility and structural stability. To achieve these goals seventeen cyanobacteria strains (over 200 identified in soils of the African countries), able to fix atmospheric N2 and to release ESP in considerable amounts were isolated, purified and grown. Using adequate techniques and procedures, large amounts of cyanobacterial biomass were produced to be applied to poor soils to ameliorate their quality and improve productivity. Laboratory and greenhouse experiments showed that the application of these biomass significantly improved overall soil fertility and crop yield, after the first crop. In spite of the need to confirm the relevance and persistence of the beneficial effect by further medium and long-term field experiments, the application of selected cyanobacteria strains to marginal lands seems to be a very promising tool for a sustainable improvement of fertility and productivity of degraded soils in semiarid tropics.