Non-point phosphorus (P) loss from agricultural land to streams is caused mainly by overland flow and leaching. In many countries P-index methods are used to identify areas at risk of P loss to streams. In flat areas with shallow groundwater levels, where losses by leaching are important, these index methods have their limitations as leaching is often not described in detail. This study presents a simple model to predict P loss by leaching at the field scale. This model called Phosphorus LEAching from Soils to the Environment (PLEASE) is based on the well-known kinetics of P in soils and lateral water flux from soils to surface waters. PLEASE was applied using readily available information to a small catchment; and a sensitivity analysis and comparison with two soil P indicators were carried out (soil P test and the phosphate saturation degree). The model predicted a total P load of 4187kg P in the Schuitenbeek catchment. The result was also a predicted P discharge at the catchment outlet of 2973kg P corrected by independent assessment of P retention in streams in the catchment (29%). This is comparable to the measured outflow (2770kg P). The calculated P losses by leaching are highly sensitive to the soil Langmuir parameters, which means that it is important to determine the adsorption isotherm to obtain reliable estimated losses. The PLEASE approach has particular value compared to other soil P indicators for estimating actual P losses by leaching from agricultural land to surface water. These results suggest that PLEASE is a promising method for quantifying differences in P loss by leaching between fields within a catchment.
- relating soil-phosphorus