Urine patch distribution under dairy grazing at three stocking rates in Ireland

Nitrate pollution of water is a serious global environmental issue. Grassland agriculture is a major source of diffuse nitrate pollution, with much of this nitrate originating from the urine patches of grazing animals. To study nitrate losses from grassland it is necessary to consider the areas of grassland that are affected by urine separately from the remainder of the pasture. Urine patches can be observed in the field as areas of vigorously growing pasture, however the pasture may continue to respond for several months, making it difficult to determine when the observed patch was actually deposited. A global positioning system was used to record the location of all urine and dung patches in a pasture at every second grazing on an Irish dairy farm during the grazing season. Any patches reappearing were removed from the data, allowing the fresh urine patches to be identified. Dairy cows deposited 0.359 urine patches per grazing hour, a value that may be used to predict the distribution of urine patches under any grazing regime. This equated to 14.1 to 20.7% of the soil surface being wet by urine annually at stocking rates of 2.0 to 2.94 cows per hectare, consistent with previous research. These values may be used in conjunction with values for nitrate loss from urine and non-urine areas to calculate nitrate losses from grazed pasture at a range of stocking rates.