Forecasting the fate of nutrients derived from organic wastes applied on soils

Abstract

Wastes organic compounds as manure, slurries, sewage sludge, composts and mixture of such biosolids reach the soils of farmer fields. Sometimes, due to unintentional applications, sewage sludge receives undesirable chemical elements or compounds, some of them being toxic for living organisms. The main question concerns the effects of the various elements of these biosolid. It is of first interest to develop experimental tools able to characterize and quantify the bioavailability of the various components for crops, mainly edible parts of the crops. One of the most efficient methods is utilizing tracer isotopes of each element. As a matter of fact, when a crop takes up a nutrient from to nutritive sources, the soil and the wastes, isotopic labeling of the two sources allows determining, in the crop, the origin of the nutrients. Experiments have been, along time, with 15N, 32P, 40K, 45Ca, 65Zn, 109Cd, 63Ni and finally a lot of isotopic tracers. This method was greatly applied for phosphorus and nitrogen. Phosphorus bioavailability of manure and slurries is near that of water-soluble inorganic P fertilizer as triple super phosphate (TSP) or diammonium phosphate (18-46). Bioavailability of P in sewage sludge depends on the chemical processes applied to the sludge and water. More water is clean, less available is the phosphorus of the wastes. An example, concerning Zn, shows that of nutrients derived from organic wastes depends on a lot of interactions taking place between the residues applied to soils and the soils components.