Nutrient Release Dynamics in Soils Amended With Municipal Solid Waste Compost in Laboratory Incubations

Two municipal solid waste composts were added to three agricultural soils developed over different parent material (schist, gabbro and granite) and incubated in two laboratory studies, in order to assess the effect of compost addition in the dynamics of soil Ca, Mg, K and P. Soils and mixtures of soil and compost (2.5% dry weight, roughly equivalent to 60 t ha−1) were incubated at 25°C for three months in a first experiment, and for five months in a second experiment. The concentrations of available Ca, Mg, K and P were determined throughout both experiments. The soils amended with compost always had higher available Ca, Mg and K concentrations than the soils without amendment. The increases were approximately 800 mg kg−1 for Ca, 30 mg kg−1 for Mg, and 150 mg kg−1 for K. Nevertheless, the concentrations of these elements did not increase with time. The available P concentrations were not increased by the addition of compost, an effect which is attributed both to microbial immobilization and to the P-fixation capacity of the soils. Therefore, the expected release of these elements in parallel to compost mineralization was not observed during the experiments, and the only fertilizing effect of the compost was that of their initial input in available forms.