Phosphorus Runoff Losses After Application of Organic Waste

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.