DISTRIBUTION OF MICROBIAL ACTIVITIES AND ORGANIC-MATTER ACCORDING TO PARTICLE-SIZE IN A HUMID SAVANNA SOIL (LAMTO, COTE-DIVOIRE)

The contributions of 6 fractions of soil organo-mineral particles of v arying sizes to soil microbial activity were studied using samples of a West African savanna soil. Fractions were obtained by a physical fra ctionation. Microbial activity was defined by CO2 production and ammon ium and nitrate + nitrite accumulations, when samples were incubated a t 28 degrees C and 80% of water holding capacity for 3 weeks. The cont ribution of each fraction was indirectly estimated by comparing the ac tivities of incomplete soils (lacking one fraction) to those of a comp letely recombined soil (all six fractions). Carbon mineralization was additive, the sum of the CO2 produced by the six fractions alone was s imilar to the quantity of CO2 produced from a complete recombined soil . Mineral nitrogen accumulation was not additive, the sum of the quant ities of total mineral N accumulated in the six fractions was greater than that of the complete recombined soil. The dynamics of net nitroge n mineralization in individual fractions depended on the nitrogen mine ralization in other fractions. (C) 1997 Elsevier Science Ltd.