1 USING NITROGEN PROCESS INHIBITORS TO REDUCE AMMONIA VOLATILISATION AND NITROUS OXIDE EMISSIONS FROM LAND APPLIED DAIRY EFFLUENT J. Li 1,2 , Y. Shi 1 , J. Luo 1 , M. Zaman 3 , W Ding 4 , D Houlbrooke 1 , S Ledgard 1 , A Ghani 1 1 Ruakura Research Centre, AgResearch, Private Bag 3123, Hamilton, New Zealand, 2 Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, China, 3 Ballance Agri-Nutrients Limited, Private Bag 12503, Tauranga 3143, New Zealand, 4 Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China. Email: jie.li@agresearch.co.nz Abstract Dairy farm effluents (manure and liquid effluent) are commonly applied to soil as a source of organic nitrogen (N) fertiliser. However, these applications increase soil inorganic N, and may therefore increase ammonia (NH 3 ) volatilisation and nitrous oxide (N 2 O) emissions. Various technologies have been used to reduce NH 3 and N 2 O losses derived from agricultural N sources, including amending N sources with N process inhibitors such as urease inhibitors (UIs) and nitrification inhibitors (NIs). The objective of our study was to measure the effect of amending different forms of dairy effluent with UI - N-(n-butyl) thiophosphoric triamide (NBTPT, commercially named Agrotain® nitrogen stabiliser) and NI - dicyandiamide (DCD). Two field experiments were conducted to study the effect of these inhibitors on NH 3 and N 2 O emissions. Treatments included fresh manure, stored manure, fresh farm dairy effluent (FDE) and stored FDE, with and without Agrotain® (0.25 g/kg N) or DCD (10 kg/ha), applied in late-winter on a free-draining volcanic soil in the Waikato region. The application rate of the FDE and manure, which had different dry matter contents (2% and 22.5%, respectively) was about 100 kg N ha -1 . Results showed that application of manure and FDE, both in fresh and stored forms, to pasture led to NH 3 volatilisation (15, 1, 17 and 0.4% of applied N in fresh manure, fresh FDE, stored manure and stored FDE lost as NH 3 , respectively). Adding UI had a significant effect (P < 0.05) on reduction of NH 3 losses from both fresh manure and fresh FDE, decreasing NH 3 emissions by 48% and 38%, respectively. All types of effluent have the potential to produce N 2 O, particularly fresh manure and fresh FDE. The emission factors (amount of N 2 O-N emitted as a percentage of applied N) of fresh manure, fresh FDE and stored FDE were 0.13%, 0.14% and 0.03%, respectively. DCD was effective in decreasing N 2 O emissions in the stored FDE, fresh FDE and fresh manure by 90%, 51% and 46%, respectively. This study showed that NBTPT can be effective in mitigating NH 3 losses and DCD in reducing N 2 O emissions from land applied dairy effluents. Key words: Ammonia, Nitrous oxide, Farm dairy effluent, Manure, Pasture, Nitrogen Introduction One of the challenges facing the dairy industry due to its rapid intensification is the need for proven effluent management systems that increase nutrient use efficiency and minimize off- farm environmental impacts. Increased animal numbers, greater use of fertiliser and higher supplementary feed inputs on dairy farms have markedly changed the volume and types of effluent produced. Effluent contains significant quantities of valuable nutrients that, if applied to land, could improve soil fertility and increase the resource use efficiency of farming systems (Luo et al., 2008; de Klein et al., 2011). A better understanding of effluent nutrient