Low losses of a P and sediment in overland flow suggest that this tillage site and others like it may not be high risk for phosphorous pollution

Abstract

This trial examined phosphorus (P) loss in overland flow (OLF) at a tillage farm in the southeast of Ireland. The soil was a grey-brown podzolic, and was representative of land covering 16% of the total agricultural area, with tillage practised on approximately one-third of this area. The object of the trial was to establish whether this site is a P-pollution risk to surface water. The productive tillage field was divided into three plots, each of approximately 1ha in size. Plots had low earth dams and open lined drains on the lower boundaries. A flow meter sampler with V-notch tank was connected to each of the three drains. Macro-pore flow (MPF) samplers were installed in the plots. Average depth of overland flow across the three plots was 5.4, 17.5 and 18.1mm y 1 for 2005, 2006 and 2007, respectively. Phosphorus concentration was 1.01, 0.64 and 0.6mg l , respectively, and P load was 0.04, 0.11 and 0.18kg ha 1 y . The median P concentration in MPF was 1.59mg l . Sediment yield (95kg ha 1 y ) was low compared to that achieved in other studies. No pollution parameter measured represented a serious pollution threat. The results of this study suggest that a large proportion of tillage land in Ireland might be classified as low risk for P loss through the overland flow pathway.