The effect of DCD on nitrogen losses from sheep urine patches applied to lysimeters in autumn

The intensification of modern pastoral agriculture has increased the risk of environmental degradation. The use of nitrification inhibitor technology has been shown to reduce nitrate (NO₃ ⁻) leaching losses and nitrous oxide (N₂O) emissions from New Zealand dairy pasture systems. However, published data on inhibitor usage to reduce these losses from intensive sheep winter grazing systems is also needed. A trial was conducted at Lincoln University using lysimeters in a Templeton silt loam soil. Four treatments (control, control + DCD, urine, urine + DCD) were applied in May 2009, with urine applied in patches at an N loading rate of 300 kg/ha with dicyandiamide (DCD) at 10 kg/ ha. Water (simulating rainfall) was applied in spring to supplement natural rainfall. Nitrous oxide gas sampling and leachate collections were made for 4 months. Application of DCD reduced the N₂O emissions by up to 72% (4.55 kg N₂O-N/ha without DCD to 1.32 kg N₂O-N/ha with DCD) from late autumn applied sheep urine and also reduced the amount of NO₃ ⁻-N leached by up to 70% (147 kg NO₃ ⁻-N/ha to 44 kg NO₃ ⁻-N/ ha). These results indicate that the use of DCD may be a useful technology to mitigate N losses from sheep break-fed pasture over winter. The need for further research in this area is discussed.This research was funded by the Lincoln University Centre for Soil and Environmental Research