Evolution of humic fraction in a redoxi-luvisol after application of granular sewage sludge.
Résumé
Agricultural use of biosolids is a way of returning carbon and nutrients to soils and a rational disposal of sewage sludge. Its use in rural environments faces some problems related to its high water content and readily fermentable status. An alternative procedure is to heat-dry the biosolids, which result in a granular product that can be handled with the same equipment used to spread granular fertilisers. A field experiment was carried out on a redoxi-luvisol in Toulouse (France) to evaluate the effects of the application of heat-dried biosolids on the amount of soil organic carbon and on the characteristics of humic and fulvic acid fractions of soil organic matter. It also sought to compare the effects of heat-dried biosolids and inorganic fertilisers on corn growth and yield. Three treatments were established by addition of granular biosolid, inorganic fertilisers and a non-fertilised control. Maize was cropped and soil organic matter content and some humic substance characteristics were monitored during a year after biosolid application. Even though the amount of carbon added as biosolid represented 28% of initial soil carbon content, biosolid application had no relevant effects either on soil organic matter content or on soil humic substance characteristics. Humic acid composition, molecular size and structure were not affected. Biosolid carbon seems to have been readily mineralised during crop cycle, so it functioned as a nutrient source without affecting soil organic matter quality
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