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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 [...]

Nitrification inhibitors can reduce nitrous oxide (N2O) emissions and nitrate leaching losses from agricultural soils. Technologies have been developed to detect and target urine patches for inhibitor application, thereby reducing the total amount of inhibitor used. However, in practice there will be a time delay between the urine deposition and inhibitor application, potentially leading to physical separation of the inhibitor and urine that could reduce the effectiveness of the inhibitor compared to when the inhibitor and urine are well mixed. In this study, 2L of cattle urine was applied on two soil types in New Zealand. Twenty-four hours later the inhibitor dicyandiamide (DCD) was applied. The soil was sampled within 18 h and again after a rainfall event. DCD concentrations were measured in the 0–20 mm, 20–50 mm, and 50–100 mm depth ranges. The movement of the urine in the soil was simulated using the HYDRUS model. Before the rain most of the DCD was within the top 20 mm and intercepted 21–29% of the urine. After the rainfall event the DCD concentration decreased in the 0–20 mm layer and increased in the 20–50 mm layer. 18–55% or 63-79% of the urine was intercepted by DCD at a concentration of >4 ppm using the measured and modelled DCD concentrations, respectively. However, only 0–27% or 0-53% of the urine was intercepted at a DCD concentration >10 ppm. [ABSTRACT FROM AUTHOR]

The objectives of this study were to improve our understanding of seasonal variation in the biophysical disappearance of the nitrification inhibitor dicyandiamide (DCD) in soil and the key regulatory factors. Changes in DCD concentrations in the soil and plant canopy were measured following application to dairy-grazed pasture soil and nongrazed pasture soil. Treatments included two levels of DCD alone (10 and 20 kg [h.sup.-1]) applied to non-grazed pasture field plots, and DCD (10 kg [h.sup.-1]) applied with urine and with urea fertiliser. DCD (10 kg [h.sup.-1]) was also applied in grazed farmlets following grazing. About 440% of the DCD applied was intercepted and stayed on the plant canopy from Additional keywords: biophysical disappearance of DCD, dicyandiamide (DCD), grazed pasture soil, nitrification inhibitor, soil temperature., Introduction Nitrous oxide ([N.sub.2]O) contributes to an enhanced greenhouse effect, with a global warming potential 298 times greater than carbon dioxide (C[O.sub.2]) in a 100-year time horizon (Forster et al. [...]

Nitrous oxide ([N.sub.2]O) from agricultural soils is a major source of greenhouse gas emissions in New Zealand. Nitrification inhibitors are seen as a potential technology to reduce these [N.sub.2]O emissions from agricultural soils. In previous studies on the effect of dicyandiamide (DCD) on [N.sub.2]O emissions from animal excreta, DCD was directly applied to urine. However, farmers apply DCD to grazed pastures shortly before or after grazing rather than applying it specifically to the urine patches. Accordingly, the objectives of this study were: (1) to test, using chamber measurements, whether the same level of [N.sub.2]O reduction is achieved under grazed conditions where excretal N is non-uniformly deposited, (2) to apply the process-based NZ-DNDC model to simulate the effect of DCD on emission reductions, and (3) to perform a sensitivity analysis on the NZ-DNDC model to investigate how uncertainties in the input parameters affect the modelled [N.sub.2]O emissions. Two circular 1260-[m.sup.2] treatment plots were grazed simultaneously for 5 h, by 20 cattle on each plot. The following day, DCD was applied in 800 L of water to one of the plots at 10 kg/ha and [N.sub.2]O emissions were measured periodically for 20 days. The cumulative [N.sub.2]O emissions were 220 ± 90 and 110 ± 20 g [N.sub.2]O-N/ha for the untreated and DCD-treated plots, respectively (based on the arithmetic mean and standard error of the chambers). This suggests a reduction in [N.sub.2]O emission from DCD application of ~50 ± 40% from a single grazing event. However, this result should be treated with caution because the possibility of sampling error due to the chamber distribution cannot be excluded. NZDNDC simulated [N.sub.2]O emissions of 169 and 68g [N.sub.2]O-N/ha for the untreated and DCD-treated areas, respectively, corresponding to a reduction of 60% in [N.sub.2]O emissions from DCD application. This level of reduction is consistent with that found in experiments with individual urine patches. [N.sub.2]O emissions found through use of NZ-DNDC were sensitive to uncertainties in the input parameters. The combined effect of varying the initial soil N[O.sup.-3] and N[H.sup.4+], soil moisture, soil organic carbon, bulk density, clay content, pH, and water-filled pore-space at field capacity inputs within plausible ranges was to change the simulated [N.sub.2]O emissions by -87% to +150%. Additional keywords: chambers, greenhouse gas mitigation, NZ-DNDC model, sensitivity analysis., Introduction Nitrous oxide ([N.sub.2]O) from agricultural soils is a major source of greenhouse gas emissions in New Zealand, accounting for 15.2% of total greenhouse gas emissions on a C[O.sub.2]a-equivalent basis [...]