Impact of cattle on soil physical properties and nutrient concentrations in overland flow from pasture in Ireland

The loss of nutrients from agricultural land to water bodies is a serious concern in many countries. To gain information on the contribution of grazing animals to diffuse nutrient losses from pasture areas to water, this study looked at the impact of cattle on nutrient concentrations in overland flow and on soil hydrology (bulk density, macroporosity and resistance to penetration). Rainfall simulations to produce overland flow were conducted and soil physical measurements were taken on experimental plots assigned to one of two treatments: (1) cattle had unrestricted access to the plot; (2) cattle could graze the plot but they could neither walk on the plot area nor deposit excrements on it. Areas to which the cattle had free access were characterised by 57–83% lower macroporosity, by 8–17% higher bulk density and by 27–50% higher resistance to penetration than areas from which the cattle were excluded. The nutrient losses from grassland that can specifically be attributed to the presence of grazing animals were found mainly in the particulate nitrogen, the organic phosphorus and in the potassium exports. Overall, the presence of cattle had a longer lasting effect on the soil hydrological parameters measured than on the nutrient concentrations in overland flow.