C AND N MINERALIZATION IN SANDY AND LOAMY GRASSLAND SOILS - THE ROLE OF MICROBES AND MICROFAUNA

A food web model was used to evaluate the role of soil microorganisms, protozoa and nematodes and their interactions on carbon and nitrogen mineralization in sandy and loamy grassland soils. The differences in C mineralization between the sites did not correspond with the differences in N mineralization. To analyse this discrepancy between the mineralization patterns, C and N mineralization rates were calculated using the observed densities of soil organisms. The C mineralization pattern could be explained from differences in the bacterial biomass estimated on each site. Food web calculations carried out to explain the discrepancy between C and N mineralization patterns indicated that faunal activity played a minor role but that the observed C and N mineralization rates could satisfactorily be calculated using different bacterial C:N ratios as determined for the soil types (8 for the sandy soils; 4.5 and 6 for the loams).