Phosphorus retention and leaching in some sandy soils of Northern Italy [Veneto]
1999
Papini, R. | Panichi, A. (Istituto Sperimentale per lo Studio e la Difesa del Suolo, Florence (Italy)) | Castelli, F. (Istituto Sperimentale per il Tabacco, Scafati, Salerno (Italy))
Phosphorus is considered a pollutant inducing eutrophication of surface water at very low concentrations. Many sandy soils have poor P retention capacity, and high rates of P applications to crops in these soils give rise to P leaching. This study was aimed at determining P adsorption capacity variation in some sandy soils, and at evaluating the hazard of P leaching in P overfertilised soils. P adsorption isotherms were determined in four tobacco cultivated sandy soils of different taxonomy near Verona. In order to evaluate P leaching after usual fertilizations and irrigations, percolating water was collected in some of the above soils during the tobacco growing seasons 1993 and 1994. The horizons with low CaCO3 content and with the P adsorption determined by Fe oxides showed a P adsorption upper limit varying from 1.4 g kg*[-1) to 3.5 g kg*[-1) P, which was unmodified by further increments of P in solution. In contrast, in soil horizons with a high CaCO3 content, P adsorption increased up to the maximum experimental concentration of P in solution (2 g l*[-1)). P concentration in percolating water was higher on soil with less P adsorption capacity. The observed soils differed markedly in their ability to hold phosphorus. Though P adsorption was high in all observed soils, where P was held mainly by Fe oxides, an elevated content of dissolved reactive P could be found in percolating water, in consequence of Fe solubility enhanced by reducing conditions
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