Short‐term Effects of Sewage‐Sludge Compost on a Degraded Mediterranean Soil

Abstract

In Mediterranean areas, often characterized by degraded soil due to recurrent fires and violent precipitation events, sewage sludge compost could improve soil properties and stimulate plant succession processes. Most of the studies dealing with compost effects on soil properties only take into account the mineral horizon compartment, without studying compost effects on organic horizon properties. In this study, we monitored the patterns of change in the litter, humus, and mineral horizon compartments in a 7‐yr‐old garrigue over 2 yr after compost spreading. Three treatments were studied: control, 50 Mg ha−1, and 100 Mg ha−1 (Fresh Mass) of cocomposted sewage sludge and green wastes. The major changes occur in the humus and litter compartments, whereas the mineral horizon is slightly affected. The mineral horizon is enriched in exchangeable K, Mg, and sporadically in P (total and available) after amendment, slightly improving overall fertility, while the humus and litter compartments keep accumulated compost organic matter and its associated nutrients, showing the slow release of elements from the chosen mature compost. Compost amendment probably enhances the humus decomposition process, first because it decreases this compartment's C/N ratio, and second because it decreases its Ni and Cr concentrations. In contrast to humus, compost should reduce the litter decomposition process, by increasing C/N ratio, pH, and concentrations of potentially toxic trace elements such as Cu, Zn, Ni, Cr, and Pb. Compost greatly enriched humus and litter in P, Cu, and Zn, and only Cu moves from organic to mineral soil horizon.