Nitrate leaching is a naturally occurring process, but when excess N is lost from N fertiliser and N deposited in urine, not only is it a loss of valuable nutrient from the farm system, it can pollute both ground and surface water. This pollution is the focus of national and regional government strategies to improve water quality.
Nitrogen from fertiliser or urine can be problematic because when added to the soil, a large proportion is converted to nitrate (NO3-) which is especially susceptible to leaching. This conversion process is known as “nitrification”. Nitrification occurs relatively slowly in winter, offering a window of opportunity for catch crops to capture some N before it is lost through leaching. Catch crops sown after winter grazing can take up significant quantities of N and reduce N leaching losses by up to 50%.
Establishing a catch crop after winter grazing can offer additional forage production perhectare, and in turn, higher farm productivity.