Loss of Phosphorus by Surface Runoff and Leaching from a Heavy Clay Soil under Barley and Grass Ley in Finland

Phosphorus losses by surface runoff and leaching were studied for three years in a 16-plot field on a heavy clay soil in south-west Finland to compare losses of total phosphorus (TP), particulate phosphorus (PP) and dissolved orthophosphate phosphorus (DP) from barley and grass ley plots. Barley was fertilized with 21 and 42 kg ha⁻¹ y⁻¹ P by placement technique. Ley was given P 42 and 84 kg ha⁻¹ y⁻¹, but split into two equal portions, by broadcasting. The mean losses of TP from the barley and ley were 1.2 and 1.6 kg ha⁻¹ y⁻¹, respectively. The PP losses (calculated as the difference between TP and DP) constituted 69% of the TP loss from barley, but only 35% of that from ley. In the case of barley, a considerable amount of PP was carried by drainage water. The mean DP losses were 0.4 kg ha⁻¹ y⁻¹ from barley and 1.0 kg ha⁻¹ y⁻¹ from ley. The higher DP loss from ley was due to both the higher fertilizer rate and the fertilizer broadcasting technique. During the second and third years of the experiment, fertilizer broadcasting on the ley plots was followed by high DP concentrations in surface runoff and drainage water. The peak DP concentrations in drainage water occurred soon after fertilizer broadcasting followed by only 7-15 mm of flow, indicating fast preferential movement of orthophosphate from the surface through the soil.