Computer-based evaluation of methods to sample nitrate leached from grazed pasture

Scientists, land managers and environmental regulators all want to quantify the amount of nitrate leached into groundwater to better understand and manage the risk of environmental contamination from agricultural land, including grazed pasture. The ability of current technology to adequately measure the nitrate leached from a grazed paddock is tested in a stochastic simulation study. Results show that impractical numbers of samplers are needed to achieve estimates accurate to within ±20% of the true value. Rather than trying to directly measure paddock-scale leaching under grazing, we suggest that further consideration be given to wider application of controlled application of nitrogen onto a few lysimeters and then extrapolate from the resulting measurements of leached nitrate to the paddock scale and beyond based on urine patch coverage