Evaluation of degree of phosphorus saturation (DPS) and easily soluble P in top- and subsoil as a predictor for P-leaching

Eutrophication has long been an environmental problem and the effects from fertilizingarable land is a known source. The degree of phosphorus saturation (DPS)and easily soluble phosphorus (P) are different variables used in different countriesto try to predict the leaching of P from soils. The purpose of this master thesiswas to investigate what variable can be used as a predictor for leached P from soilsand to investigate what extent P leaching from the topsoil can be readsorbed inthe subsoil. The extraction method used for DPS was the Swedish standard lactateextraction and for easily soluble P were distilled water, CaCl2-solution and artificialrainwater with recipe from SMHI used. Three different soils in Sweden were used,two arable soils with different chemical properties and one forest soil. The soilswere filtered (2 mm) and put into columns since the texture was of interest ratherthan the structure. CaCl2-solution was used to saturate the samples and artificialrainwater was used for irrigation. The results showed that easily soluble P is areasonable indicator for leached P and that the subsoil affects the total leachingof P. However, no significant correlation was found between DPS and leached P,indicating that it may not be a suitable indicator of leaching. On the other hand,DPS can be seen as a reasonable indicator for easily soluble P since the correlationtest showed almost significant correlation. The results also showed that the electricconductivity in the leachate correlates to the leached P for the arable soils. For amore reliable result, more soils should be analyzed during more days