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The objective of this laboratory incubation study was to assess the effectiveness and longevity of urease inhibitor N-(2-nitrophenyl) phosphoric triamide (2-NPT), along with the commonly used N-(n-butyl) thiophosphoric triamide (nBTPT), in reducing ammonia (N[H.sub.3]) emissions from cattle urine applied to pasture soils. It was hypothesised that 2-NPT would be effective as a longer-lasting inhibitor to reduce emissions after the deposition of urine during multiple grazing events. Two dairy-grazed pasture soils (Fluvisol, Rangitikei loamy sand (RLS) and Andosol, Egmont black loam (EBL)) with contrasting organic carbon levels and urease activity were used. The following treatments were applied to the soils at the start of the experiment: no inhibitor, nBTPT-low, 2-NPT-low, 2-NPT-medium and 2-NPT-high. Urine-N was applied to all the treatments at four stages: immediately before inhibitor application (Stage A), 29 days after inhibitor application (Stage B), 56 days after inhibitor application (Stage C) and 29 days and again 60 days after inhibitor application (Stage D); N[H.sub.3] emissions were measured up to Day 31 after each urine application. The low, medium and high application rates of inhibitors were determined based on achieving 0.025%, 0.050% and 0.075% of quantity of urine-N applied in Stage A respectively. For the no inhibitor treatment, the proportion of total applied N in urine that was emitted as N[H.sub.3] for the different stages ranged from 35.8% to 50.5% for RLS soil and from 14.2% to 26.7% for EBL soil. For Stage A, both inhibitors equally reduced N[H.sub.3] emissions from applied urine in both soils (23.7-27.3% for the RLS and 20.6-27.2% for the EBL). For Stage B, significant reductions (4.2-13.4%) in N[H.sub.3] emitted was observed only from RLS soil, with there being a significantly greater reduction from 2-NPT than from nBTPT, and 2-NPT continued to reduce N[H.sub.3] emissions at Stage C (5.6-7.4%). There was no reduction in emissions during Stage D by either of the inhibitors. The results of this study suggest that 2-NPT can extend the longevity of urease inhibition and reduce N[H.sub.3] emissions compared with the more commonly used inhibitor nBTPT in dairy-grazed pasture soils. Additional keywords: dairy soils, environmental degradation, nitrogen loss, nitrogen use efficiency, soil pH, urea hydrolysis. Received 11 November 2018, accepted 31 May 2019, published online 23 July 2019, Introduction The intensification and expansion of dairy farming in New Zealand (NZ) over the past three decades has resulted in a significant rise in the amount of cattle urine being [...]

Micronutrients copper (Cu) and zinc (Zn) have the potential to inhibit soil urease activity (UA) and reduce ammonia (N[H.sub.3]) emissions over long duration (8-12 weeks) but have not been tested for reducing N[H.sub.3] losses from cattle urine deposited in dairy-grazed pasture soils. The objective of this study was to assess the effectiveness and longevity of Cu and Zn in reducing soil UA, for the use of these metals to reduce N[H.sub.3] emissions from deposited urine by grazing cattle. A series of experiments were conducted to (i) assess the relationship between inherent Cu and Zn status and soil UA of New Zealand dairy-grazed pasture soils, (ii) determine the impact of Cu and Zn addition to pasture soils on soil UA and (iii) investigate how soil organic carbon (C) and other C-related textural and mineralogical properties such as clay content and cation exchange capacity influence the effectiveness of added Cu and Zn in reducing urea hydrolysis. The results showed significant positive correlations of soil total C and total nitrogen (N) with soil UA. However, there were no significant negative correlations of soil UA with inherent Cu and Zn levels. Similarly, addition of Cu and Zn to soil did not significantly reduce soil UA. However, when Cu was added to two different soil supernatants there was a significant reduction in hydrolysis of urea applied at 120 and 600 mg urea-N [kg.sup.-1] soil. Additions of Zn achieved negligible or small reductions in urea hydrolysis after 120 and 600 mg urea-N [kg.sup.-1] soil applications to soil supernatants. This result suggests that Cu can inhibit soil UA and urea hydrolysis in soil supernatants with potentially low C, clay and cation exchangeable base contents. However, the interaction of bioavailable Cu with labile soil organic C and clay particles leads to its inactivation, resulting in ineffectiveness in organic C-rich pasture soils. Although most of the added Zn did not complex and remained bioavailable, the observed levels of bioavailable Zn had limited effect on soil UA. Additional keywords: ammonia emissions, clay content and cation exchange capacity, metal bioavailability, nitrogen loss, nitrogen use efficiency, soil organic carbon, urease inhibition., Introduction Intensification of dairy farming in New Zealand (NZ) over the last three decades has resulted in a substantial increase in the national dairy herd size from 2.3 million cows [...]