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 thre e 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 l ey plots. Barley was fertilized with 21 and 42 kg ha(-1) y(-1) P by pl acement technique. Ley was given P 42 and 84 kg ha(-1) y(-1), but spli t 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. Th e PP losses (calculated as the difference between TP and DP) constitut ed 69% of the TP loss from barley, but only 35% of that from ley. In t he 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 bot h the higher fertilizer rate and the fertilizer broadcasting technique . During the second and third years of the experiment, fertilizer broa dcasting on the ley plots was followed by high DP concentrations in su rface runoff and drainage water. The peak DP concentrations in drainag e water occurred soon after fertilizer broadcasting followed by only 7 -15 mm of flow, indicating fast preferential movement of orthophosphat e from the surface through the soil.