How does the application of different nitrification inhibitors affect nitrous oxide emissions and nitrate leaching from cow urine in grazed pastures?

Abstract

Nitrous oxide (N₂O) is a potent greenhouse gas, and nitrate (NO₃⁻) is a water contaminant. In grazed grassland, the major source of both NO₃⁻ leaching and N₂O emissions is nitrogen (N) deposited in animal excreta, particularly in the urine. The objective of this study was to determine the effectiveness of two nitrification inhibitors: (i) a solution of dicyandiamide (DCD) and (ii) a liquid formulation of 3,4-dimethylpyrazole phosphate (DMPP) for reducing N₂O emissions and NO₃⁻ leaching from urine patch areas in two grazed pasture soils under different environmental conditions. In the Canterbury Templeton soil, the nitrification rate of ammonium from the animal urine applied at 1000 kg N/ha was significantly decreased by the application of DCD (10 kg/ha) and DMPP (5 kg/ha). N₂O emissions, measured over a 3-month period, from dairy cow urine applied to the Canterbury Templeton soil were 1.14 kg N₂O-N/ha, and this was reduced to 0.43 and 0.39 kg N₂O-N/ha by DCD and the liquid DMPP, respectively. These are equivalent to 62–66% reductions in the total N₂O emissions. Nitrate leaching losses from dairy cow urine applied to the Waikato Horotiu soil lysimeters were reduced from 628.6 kg NO₃⁻-N/ha to 400.6 and 451.5 kg NO₃⁻-N/ha by the application of DCD (10 kg/ha) or DMPP (1 kg/ha), respectively. There was no significant difference between the DCD solution and the liquid DMPP in terms of their effectiveness in reducing N₂O emissions or NO₃⁻ leaching under the experimental conditions of this study. These results suggest that both the liquid formulations of DCD and DMPP have the potential to be used as nitrification inhibitors to reduce N₂O emissions and NO₃⁻ leaching in grazed pasture soils.