UFRPE — Department of Agronomy, Recife, Brazil

Abstract

The purpose of this work was to obtain economic products with high levels of available P to be used as alternatives to soluble fertilisers. To evaluate the effect of sulphur inoculated with Acidithiobacillus on the available P in rock phosphate and addition of various forms of organic matter, a greenhouse experiment using a Brazilian tableland soil was conducted. Mimosa caesalpiniifolia inoculated with rhizobia was used as the test plant. The experiment was a factorial (4 × 6) arranged in a randomised block design, with 3 replicates. P treatments were: triple superphosphate (TSP) 100 kg/ha P; rock phosphate at rates of 500 and 1000 kg/ha, pelleted with sulphur at 50 and 100 kg/ha S, respectively, inoculated with Acidithiobacillus (+Ac.) and without Acidithiobacillus (−Ac.); and a control without phosphorus (P₀). Organic matter treatments were: coconut powder at levels of 5 t/ha (CP₅) and 10 t/ha (CP₁₀); Fibrasil 5 t/ha (FB₅); and no added organic matter (OM₀). Nitrogenase activity, nodulation, shoot dry matter, total N and total P in shoot dry matter and soil pH were determined. P treatments had no effect on plant height, nodulation and nitrogenase activity. Rock phosphate pelleted with S inoculated with Acidithiobacillus plus Fibrasil produced the biggest plants and the highest N and P uptake. Rock phosphate with S and Acidithiobacillus increased available P and reduced soil pH, especially combined with Fibrasil residue, with no inhibitory effect on plant growth. The P biofertilisers and the organic by-products showed potential to benefit smallholder farmers.

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