ORIGINAL PAPER Effect of rhizobia and rock biofertilizers with Acidithiobacillus on cowpea nodulation and nutrients uptake in a tableland soil

Abstract Chemical fertilizers have been used in the cul-tivation of plants due to their high solubility and effect on crops yield. Biofertilizers with phosphate rock (PR) and potash rock (KR) plus sulfur inoculated with Acidithioba-cillus may improve plant growth and contribute to addition of available P and K in soil. The effectiveness of biofertil-izers from phosphate and potash rocks mixed with sulfur and Acidithiobacillus was studied in a Typic Fragiuldult soil of the Brazilian Northeast Tableland. Cowpea (cv. ‘‘IPA 206’’) was grown with and without rhizobia inoculation. Treat-ments were: (a) phosphate rock (1000 kg ha-1); (b) Biofertilizers-BP (250 and 500 kg ha-1); (c) triple super-phosphate-TSP (250 kg ha-1); (d) potash rock (1000 kg ha-1); (e) biofertilizer-BK (250; 500 and 750 kg ha-1); (f) potassium chloride-KCl (250 kg K20 ha-1); (g) control without P or K fertilization (P0K0). The soil was maintained under water submersion covered with black plastic (solari-zation process) for a period of 30 days. Biofertilizers (Bp and BK) and soluble fertilizers increased plant growth and NPK uptake. Biofertilizers reduced soil pH, especially when applied in highest rates. Biofertilizers and TSP+KCl showed the best values of available P and K in soil. Rhizobial inoc-ulation was effective on cowpea, but no nodules were formed by bacteria native from the soil, probably due to the effect of the solarization process. From obtained PK biofertilizers could be used as alternative for cowpea fertilization in Tableland soils