Effects of Lime and Phosphorus Application on Phosphorus Runoff Risk

Lime was investigated as a soil amendment to decrease phosphorus (P) loss in runoff from two Delaware sandy loam soils, one high and one low in P. Soils were limed at three rates (control and target pH values of 6 and 6.8, respectively), packed into runoff boxes (2,000 cm(2)) and received simulated rainfall (80 mm h(-1) for 30 min). Lime showed potential to decrease P loss in runoff, but its effectiveness was soil specific and dependant on other management factors also. Lime decreased dissolved reactive P (DRP) and dissolved organic P (DOP) loss by 20-25 and 52-93 %, respectively, for the high-P soil and particulate P (PP) by 13 % for the low-P soil. The majority of P lost in runoff was DOP (3-29 %) or PP (64-96 %). Lime increased PP losses from the finer-textured soil following P application, indicating that increased P sorption can lead to increased losses if P is sorbed to more erodable particles. Initial soil P status was more important than liming in determining P loss. While amendments may decrease P losses in the short term, addressing nutrient imbalances at the field scale is clearly necessary in the long term. Losses increased significantly following inorganic P application. Although P was sorbed rapidly, with less than 2 % of added P removed in runoff, mean concentrations in excess of 700 mu g l(-1) DRP, 2,500 mu g l(-1) OP and 6,500 mu g l(-1) PP were recorded for both soils immediately following P application.