A lysimeter study of the impact of cow urine, dairy shed effluent, and nitrogen fertiliser on nitrate leaching

The effect of cow urine, dairy shed effluent (DE), and urea fertiliser on n itrate leaching was determined using undisturbed soil lysimeters (500 mm di ameter by 700 mm deep) with ryegrass (Lolium perenne){white clover (Trifoli um repens) pasture. Cow urine was applied to the lysimeters, at rates of 0 and 1000 kg N/ha in May 1996. Urea and DE were applied to urine-applied and non-urine-applied lysimeters at rates of 0, 200, and 400 kg N/ha in 4 spli t equal applications in May, August, and November 1996 and February 1997. N atural rainfall was supplemented with simulated rainfall in winter and spri ng (May-October) to achieve the 75th percentile of winter-spring rainfall r ecords in the region. Flood irrigation was applied 6 times during summer-au tumn (November{April) at 100 mm per application, which is a typical practic e used by dairy farmers in the region. Drainage water was collected and ana lysed for nitrate, nitrite, bromide (added tracer), and ammonium. Over the first year of the experiment (May 1996{April 1997), 12% of the uri ne-N applied was lost through leaching, mainly in nitrate form. When urine (1000 kg N/ha) was applied in combination with DE (200 kg N/ha) and urea (2 00 kg N/ha), the mineral N leaching loss increased to 14% of the total N ap plied. The annual average nitrate concentrations in the drainage from the l ysimeters that received urine alone, or urine+DE and/or urea, were 33-57 mg N/L, with a mean peak concentration of 110 mg N/L. These nitrate concentra tions were significantly higher than in those treatments that did not recei ve urine (1-5 mg N/L). Because, on average, about 25% of the area of a grazed dairy paddock receiv es urine per year, the field-scale leaching losses were calculated by takin g into account the dilution erect of drainage water from non-urine patch ar eas of the paddock. The calculated annual paddock losses were 33-60 kg N/ha , and on average the annual paddock nitrate concentrations were 10-17 mg N/ L. This demonstrates the importance of accounting for the dilution of nitra te in the leachate from non-urine patch areas of the paddock. The annual average concentration from the treatment DE at 400 kg N/ha was s ignificantly lower than that from the urea treatment at the same rate. This was probably because of the different chemical forms of N in each material , and needs to be taken into account when developing regional rules for lan d application of urea and effluents.