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.
In this work, phosphorus (P) losses due to runoff were evaluated to understand the factors influencing the processes by which this element is lost. The forms of P present in organic wastes were studied using information provided by three P fractionation methods. All three methods contributed successfully to the understanding of the P forms present in wastes. However, it is difficult to compare the results from each to one another, as each protocol employs different extraction methods and times. In parallel, simulated rain systems were developed according to the "National Phosphorus Research Project" (2001) to characterize the P lost in the surface runoff generated. Experiments were performed on soil dosed with organic wastes applied both superficially and by mixing with the soil, and significant differences were found in the amounts of P determined to be in the runoff water of each, in both solution and particulate forms. Losses in experiments in which organic waste was applied to the soil surface were larger than those in experiments in which the samples mixed. In general, losses during the first rainfall event were the highest and particulate P forms predominated over dissolved forms. In mixed samples, significant differences in results were found depending on the type of waste used. Finally, a positive relationship was found between various P forms determined by sequential fractionation protocols and P losses by runoff.
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