Long Term Effects of Biosolid Applications on Soil Biological Parameters

For more than 15 years, there has been a progressive reinforcement of legislation related to biosolidutilization in the EU, particularly in France. There is a particular concern about effects on soilorganisms, even though sludge spreading has been shown to have a favorable effect on soil biologicalcharacteristics by stimulating microbial activity and biomass. Generally, soil amendment oforganic matter via sludge application also favors soil invertebrates and abundance of Carabidae,earthworms, nematodes, and mesofauna. However, the responses of organisms to sludgeapplication are specific. Changes in microbial and invertebrate community structure such as a decreaseof species and functional diversity was also observed, especially if sludge is contaminated by heavymetals.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 toeach plot (40 m2) according to regulations (four applications of 10 t ha−1 within 10 yr, representing 160kg of dry matter for each plot). Spreadings have stopped in 2002, and soil biological assessment wascarried out in 2010. Biological indicators included bacterial diversity, enzymatic activity,microarthropods and macrofauna abundance and diversity. Some functional indicators, includingbiostructures, were also studied.Pedologic and agronomic effects have shown the positive effect of biosolids on soil fertility, withoutserious contamination by heavy metals or organic pollutants. The present results concerning soilbiota show no significant effect on soil biota and functional parameters measured.