Nitrogen leaching losses from different forms and rates of farm effluent applied to a Templeton soil in Canterbury, New Zealand

The leaching losses of nitrogen from a range of farm effluents and wastes, including pig slurry, dairy pond sludge, farm-dairy effluent, and cow urine are compared on a Templeton fine sandy loam. At similar rates of application, leaching losses decreased in the following order: cow urine>pig slurry>farm-dairy effluent>dairy pond sludge. The susceptibility to leaching is determined by the forms of the N in the waste, and a high N :C ratio alone is not an adequate predictor of leaching intensity. Nitrate is most susceptible to leaching, followed by ammonium and organic forms of N. Splitting the applications of effluent into two or four portions applied at different times reduced the overall quantity of nitrate leached by c. 30%, depending on the waste. Similarly, reducing the overall rate from 400 to 200 kg N/ha also reduced the N leaching loss by c. 30%, depending on the particular waste. It is recommended that the land application of farm waste be based on a knowledge of the propensity of different kinds of wastes to contaminate groundwater, especially with nitrate-N. An effective mitigation technology to reduce nitrate leaching from grazed pasture soils is to treat the soil, including cow urine areas, with a nitrification inhibitor, e.g., dicyandiamide (DCD), which has been found to reduce nitrate leaching losses by 60%, decrease nitrous oxide emissions by over 75%, and increase pasture yield by over 10%.