Phosphorus Leaching from an Organic and a Mineral Arable Soil in a Rainfall Simulation Study.

Phosphorus derived from agricultural systems has been found to cause eutrophication of surface waters. To combat this, the specific location of soil profile P release is necessary for development of effective mitigation strategies. This paper describes a P leaching study of two Swedish arable soils, an organic (Typic Haplosaprist) and a mineral soil (Typic Hapludalf), both with high P content. Undisturbed soil columns isolated 0- to 20-, 20- to 40-, 40- to 60-, and 60- to 80-cm depth intervals. These were placed in a rainfall simulator and subjected to four 50-mm rainfall events to identify the origin of P leachate as a function of soil depth interval and physicochemical properties. Phosphorus losses were greatest from the two uppermost layers of both soils after 200 mm of artificial rainfall was applied at 5 mm h. Total P concentration in leachate from the 0- to 20-cm layer ranged from 2.1 to 8.8 mg L for the mineral and 3.7 to 10.3 mg L from the organic soil, with most (95-100%) in dissolved reactive P form. Degree of P saturation correlated well with total P leaching losses from the organic soil ( = 0.84) but not the mineral soil ( = 0.69), suggesting that the presence of Al and Fe (hydr)oxides has a stronger influence on P leaching in the organic soil. Results indicate that both soils have the potential to contribute concentrations of P above those known to cause eutrophication of surface waters.