Risk of leaching in soils amended by compost and digestate from municipal solid waste.

New European directives have proposed the direct application of compost and digestate produced from municipal solid wastes as organic matter sources in agricultural soils. Therefore information about phosphorus leaching from these residues when they are applied to the soil is increasingly important. Leaching experiments were conducted to determine the P mobility in compost and digestate mixtures, supplying equivalent amounts to 100 kg P ha(-1) to three different types of soils. The tests were performed in accordance with CEN/TS 14405:2004 analyzing the maximum dissolved reactive P and the kinetic rate in the leachate. P biowaste fractionation indicated that digestate has a higher level of available P than compost has. In contrast, P losses in leaching experiments with soil-compost mixtures were higher than in soil-digestate mixtures. For both wastes, there was no correlation between dissolved reactive P lost and the water soluble P. The interaction between soil and biowaste, the long experimentation time, and the volume of leachate obtained caused the waste's wettability to become an influential parameter in P leaching behavior. The overall conclusion is that kinetic data analysis provides valuable information concerning the sorption mechanism that can be used for predicting the large-scale behavior of soil systems.

Fractionation of phosphorus biowastes: characterisation and environmental risk.

Phosphorus (P) fertilizer is essential for food production and is a limiting factor in crop yields. However, the role of P in the eutrophication of surface water has long been recognised. During recent years, the input of P from agriculture to surface waters has increased and has been the focus for strategies aimed at mitigating diffuse P losses. As not all forms of P have the same availability, it is important to know the main forms of phosphorus in biowastes, and hence to develop fractionation schemes. The standards, measurements, and testing (SMT) procedure for phosphorus fractionation in freshwater sediments, developed within the framework of the Standards, Measurements, and Testing Program of the European Commission, was applied to 15 biowastes used frequently in agriculture, to obtain total P, inorganic and organic P, apatite P, and non-apatite inorganic P. The Hedley method was applied to determine the water-soluble phosphorus (WSP) in all the biowastes. In addition, the aluminium, calcium, and iron concentrations were quantified and related to the WSP. The results confirm the applicability of the SMT protocol to all kinds of waste usually applied in agriculture. The SMT protocol revealed the existence of large amounts of inorganic P and non-apatite inorganic P, the most-available forms of P for all the biowastes. The comparison of the data for total P (SMT protocol) and WSP (Huang protocol) does not show a good linear relationship between these parameters. Instead, the relationship between [aluminium+calcium+iron] and WSP is a better indication of the availability of P.