Long Term Effects of Biosolid Applications on Soil Biological Parameters

National audienceFor more than 15 years, there has been a progressive reinforcement of legislation related to biosolid utilization in the EU, particularly in France. There is a particular concern about effects on soil organisms, even though sludge spreading has been shown to have a favorable effect on soil biological characteristics by stimulating microbial activity and biomass. Generally, soil amendment of organic matter via sludge application also favors soil invertebrates and abundance of Carabidae, earthworms, nematodes, and mesofauna. However, the responses of organisms to sludge application are specific. Changes in microbial and invertebrate community structure such as a decrease of species and functional diversity was also observed, especially if sludge is contaminated by heavy metals. The present results aimed to assess effects of different biosolids, including sewage sludge, composts, coal ashes and household waste ashes on soil biota. Each type of biosolid was applied manually to each plot (40 m2) according to regulations (four applications of 10 t ha−1 within 10 yr, representing 160 kg of dry matter for each plot). Spreadings have stopped in 2002, and soil biological assessment was carried out in 2010. Biological indicators included bacterial diversity, enzymatic activity, microarthropods and macrofauna abundance and diversity. Some functional indicators, including biostructures, were also studied. Pedologic and agronomic effects have shown the positive effect of biosolids on soil fertility, without serious contamination by heavy metals or organic pollutants. The present results concerning soil biota show no significant effect on soil biota and functional parameters measured