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The aim of this study was to evaluate the effectiveness of a mixed biofertilizer with phosphate and potash rocks (PK biofertilizer) combined with an earthworm compound inoculated with free living diazotrophic bacteria and Cunninghamella elegans, fungi that produces chitosan, on cowpea nodulation, biomass yield and nutrient uptake. The effects of some chemical attributes from an acidic soil of the Brazilian Northeast were also studied. The treatments were as follows: a) biofertilizer enriched in N by free living diazotrophic bacteria(NPKB), applying crustaceous chitosan (ChCru) at a rate 2 mg mL -1 ; b) NPKB and ChCru at a rate 4 mg mL -1 ; c) NPKB and ChCru at a rate 6 mg mL -1 ; d) NPKB and fungi chitosan (ChFu, 2 mg mL -1); e) NPKB+C. elegans (NPKP); f) NPKB without chitosan; g) mineral fertilizers (NPKF); and h) control without NPK fertilizer and chitosan. Biofertilizer treatments increased cowpea nodules biomass, shoot biomass, and total N, P, and K in the shoots. The largest increase was obtained with ChCru, and the highest rate was obtained with NPKP. Furthermore, biofertilizers reduced soil pH and increased the total N and available P and K. These results reveal the potential of rock biofertilizer mixed with earthworm compound inoculated with free living diazotrophic bacteria and C. elegans (fungi chitosan) for plant production and nutrient uptake. The biofertilizer may be an alternative for NPK fertilization that slows the release of nutrients, favoring longterm soil fertility.

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A greenhouse experiment was carried out from January–May 2001, to evaluate the effects of elemental sulphur inoculated with Thiobacillus, compared with gypsum, in the amendment of two saline sodic soils (Neosol Fluvic Salic sodic) from the Brazilian semi-arid region, and on growth of the tropical legumes cowpea and yam bean, inoculated with specific rhizobia strains. The treatments consisted of sulphur rates (0·6, 1·2 and 1·8 t/ha) and gypsum (1·8 and 3·6 t/ha), and irrigation water containing the salts NaHCO3, MgCl2, CaCl2, NaCl and KCl, with electrical conductivity 0·2 dS/m at 25 °C. There was a treatment with no sulphur or gypsum applied. The correctives increased Na+ and electrical conductivity on leached solution, and decreased soil pH and exchangeable cations, especially Na+. Sulphur inoculated with Thiobacillus was more efficient than gypsum, reducing soil-exchangeable sodium. Sulphur with Thiobacillus in Soil 1 reduced pH (8·2 to 4·7) and electrical conductivity of the soil saturation extract (15·3 to 1·7 mS/cm) to values below those used for classification as saline and sodic soil. The growth of the tropical legumes cowpea and yam bean was increased by rhizobia inoculation when soil ameliorants were used, especially sulphur in combination with Thiobacillus.

Gypsum and sulfur have been used as amendments for application in sodic and saline sodic soils, lthough gypsum is not effective in soil pH reduction. In this study the combined effects of elemental sulfur inoculated with Acidithiobacillus (S*) and gypsum (G) in chemical attributes of a Brazilian solodic soil was evaluated. The treatments consisted in addition of S* and G in various levels (0, 0.8, 1.6, 2.4, and 3.2 t ha -1 ) and different mixing proportions (100:0, 75:25, 50:50, 25:75, and 100:0), acting during 15, 30, and 45 days. Sulfur inoculated with Acidithiobacillus (S*) markedly reduced soil pH in the leaching solution, especially when applied in the highest levels. Gypsum or sulfur applied individually was not satisfactory for soil reclamation. At 15 days of incubation Na + , Ca 2+ , and Mg 2+ showed higher values in the leaching solution, and a marked decrease was observed in the leaching solution at 30 days. Reduction in soil electrical conductivity and in exchangeable Na + , Ca 2+ , and Mg 2+ was observed and in a general way best results were achieved with S* : G in the ratio 50:50, using 2.4 and 3.2 t ha -1 . Sulfur with Acidithiobacillus was more effective than gypsum in decreasing soil pH, and sulfur applied with gypsum in the proportion 50:50 showed the best results in relation to exchangeable sodium and electrical conductivity and showed values below those used for classification as sodic soils.

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