Phosphorus leaching through intact soil cores as influenced by type and duration of manure application

Leaching of phosphorus (P) in manure-amended soils has received increased attention as a significant source of non-point source P pollution. Intact soil cores were collected from fields on a farm in Southern New York to test the effects of long-term dairy or poultry manure application on P leaching. Nine fields were selected (four poultry, four dairy, and one unamended) to represent a broad range of P saturation levels (5.3 to 62.4%) in the topsoil (0-7.5 cm). Water was applied weekly at a rate matching a 1-year return period storm for the study area (230 mm h(-1)). Dissolved reactive P (DRP) losses in leachate from all soil cores ranged from 0.007 to 0.055 kg P ha(-1), except in two fields with long-term histories of dairy and poultry manure application, where losses averaged 0.21 and 0.45 kg P ha(-1), respectively. Hydrographs of the field with the dairy manure history suggested preferential flow as an explanation of leachate P enrichment. In the poultry manure amended field, high levels of soil P saturation throughout the profile suggested subsoil P desorption as a factor controlling leachate P. Surface application of dairy manure to the soil cores (167 kg total P ha(-1)) increased the mean leachate DRP concentration from 1.5 to 10.5 fold. After five leaching events spanning 22 days, DRP concentrations remained 2.0 to 13.4 fold above pre-manure application levels. This study points to saturation of P in subsoils by long-term manure application as a key concern to P loss in leachate and highlights the role of annual manure additions on subsurface P loss potential.