Nutrient release from composts into the surrounding soil

Improved understanding of the effect of compost application on soil properties is critical for optimizing the desired effects of compost application. However there are no studies on the effect of composts on soil properties within the first centimetres of the compost layer. In this microcosm study three composts from different feedstocks, namely C1 (from animal manures) and C2 and C3 (from the organic fraction and municipal solid waste) were applied as a layer which was separated from the soil by a mesh. Microcosms without compost served as controls. Microbial and chemical properties of the soil were determined at 0–5 and 5–10 mm distance from the mesh after 30 and 63 days. During the 63 day incubation, the total C, N and P and available N concentrations in the composts decreased whereas the available P concentration increased. The composts induced higher microbial biomass and activity, total organic C and available N and P concentrations up to 10 mm into the surrounding soil with greater effects after 30 than after 63 days. The increase in nutrient concentrations was generally greater in soil adjacent to the two finer-textured composts with the higher nutrient concentration (C1 and C3) than in the coarser-textured compost (C2) which had lower nutrient concentrations, however the differences in nutrient concentrations in the soil were small compared to those among the composts. The 0–5 and 5–10 mm layers did not differ in most of the measured properties except for greater soil respiration and N and P availability in the 0–5 mm layer. It is concluded that composts release nutrients into the surrounding soil over a period of 2 months which increase nutrient availability and microbial activity, with the zone of influence extending at least 10 mm from the compost-soil interface.

► Composts released N and P over the 63 day incubation period into the adjacent soil.
► The N and P concentrations in the soil were greater after 30 than after 63 days.
► The finer-textured composts released more N and P than the coarse-textured compost.
► Differences in nutrient concentration in the soil were smaller than between composts.