Urease and nitrification inhibitors with pig slurry effects on ammonia and nitrous oxide emissions, nitrate leaching, and nitrogen use efficiency in perennial ryegrass sward

OBJECTIVE: The present study was conducted to assess the effect of urease inhibitor (hydroquinone [HQ]) and nitrification inhibitor (dicyandiamide [DCD]) on nitrogen (N) use efficiency of pig slurry for perennial ryegrass regrowth yield and its environmental impacts. METHODS: A micro-plot experiment was conducted using pig slurry-urea (15)N treated with HQ and/or DCD and applied at a rate of 200 kg N/ha. The flows of N derived from the pig slurry urea to herbage regrowth and soils as well as soil N mineralization were estimated by tracing pig slurry-urea (15)N, and the N losses via ammonia (NH(3)), nitrous oxide (N(2)O) emission, and nitrate (NO(3)(−)) leaching were quantified for a 56 d regrowth of perennial ryegrass (Lolium perenne) sward. RESULTS: Herbage dry matter at the final regrowth at 56 d was significantly higher in the HQ and/or DCD applied plots, with a 24.5% to 42.2% increase in (15)N recovery by herbage compared with the control. Significant increases in soil (15)N recovery were also observed in the plots applied with the inhibitors, accompanied by the increased N content converted to soil inorganic N (NH(4)(+)+NO(3)(−)) (17.3% to 28.8% higher than that of the control). The estimated loss, which was not accounted for in the herbage-soil system, was lower in the plots applied with the inhibitors (25.6% on average) than that of control (38.0%). Positive effects of urease and/or nitrification inhibitors on reducing N losses to the environment were observed at the final regrowth (56 d), at which cumulative NH(3) emission was reduced by 26.8% (on average 3 inhibitor treatments), N(2)O emission by 50.2% and NO(3)(−) leaching by 10.6% compared to those of the control. CONCLUSION: The proper application of urease and nitrification inhibitors would be an efficient strategy to improve the N use efficiency of pig slurry while mitigating hazardous environmental impacts.