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Soil samples from a rainforest, a papaya plantation, a pure Brachiaria humidicola pasture and a B. humidicola/Desmodium ovalifolium mixture were analyzed for fertility parameters. Soils were sieved to >100 µm and the organic matter light fraction was obtained by 1.8 g mL⁻¹ density separation in a sodium polytungstate solution which was subsequently incubated under anaerobic conditions. The effect of different density agents (sodium polytungstate, Ludox and sodium iodide) on mineralization was also tested on a temperate and a tropical soil and on maize tissue.

Anaerobic incubation of light fractions of tropical topsoils (0-2 cm) demonstrated a good differentiation between the compared management treatments whereas mineralization potentials of whole soil samples were less contrasting. Samples from the rainforest showed the highest mineralization values and those from the plantation the …