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Item Meta-analysis of New Zealand's nitrous oxide emission factors for ruminant excreta supports disaggregation based on excreta form, livestock type and slope class.(Elsevier B.V., 2020-08-25) van der Weerden TJ; Noble AN; Luo J; de Klein CAM; Saggar S; Giltrap D; Gibbs J; Rys G; Jenerette DGlobally, animal excreta (dung and urine) deposition onto grazed pastures represents more than half of anthropogenic nitrous oxide (N2O) emissions. To account for these emissions, New Zealand currently employs urine and dung emission factor (EF3) values of 1.0% and 0.25%, respectively, for all livestock. These values are primarily based on field studies conducted on fertile, flatland pastures predominantly used for dairy cattle production but do not consider emissions from hill land pastures primarily used for sheep, deer and non-dairy cattle. The objective of this study was to determine the most suitable urine and dung EF3 values for dairy cattle, non-dairy cattle, and sheep grazing pastures on different slopes based on a meta-analysis of New Zealand EF3 studies. As none of the studies included deer excreta, deer EF3 values were estimated from cattle and sheep values. The analysis revealed that a single dung EF3 value should be maintained, although the value should be reduced from 0.25% to 0.12%. Furthermore, urine EF3 should be disaggregated by livestock type (cattle > sheep) and topography (flatland and low sloping hill country > medium and steep sloping hill country), with EF3 values ranging from 0.08% (sheep urine on medium and steep slopes) to 0.98% (dairy cattle on flatland and low slopes). While the mechanism(s) causing differences in urine EF3 values for sheep and cattle are unknown, the 'slope effect' on urine EF3 is partly due to differences in soil chemical and physical characteristics, which influence soil microbial processes on the different slope classes. The revised EF3 values were used in an updated New Zealand inventory approach, resulting in 30% lower national N2O emissions for 2017 compared to using the current EF3 values. We recommend using the revised EF3 values in New Zealand's national greenhouse gas inventory to more accurately capture N2O emissions from livestock grazing.Item Mitigation potential of urease inhibitory compounds in reducing ammonia emissions from cattle urine in dairy-grazed pasture soils : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) in Soil Science at Massey University, Palmerston North, New Zealand(Massey University, 2019) Adhikari, Kamal PrasadThe excretal deposition by grazing animals, especially urine containing about 80% urea, and urea fertiliser use on pastoral farms are major sources of ammonia (NH₃) emissions in New Zealand (NZ) agriculture. Recent intensification of dairy farming in NZ has resulted in a substantial increase in the use of nitrogen (N) fertiliser, especially urea, and the quantity of urine deposited by grazing dairy cows onto pasture soils, and as a consequence, higher NH₃ emissions. These emissions represent economic and environmental losses. The urease inhibitor (UI) N-(n-butyl) thiophosphoric triamide (nBTPT) has shown effectiveness in reducing emissions when applied with fertiliser urea or cattle urine in NZ dairy-grazed pasture soils. However, the inhibitory effect of nBTPT on reducing NH3 emissions is effective for a relatively short period (7 - 14 days), during which emissions from urea fertiliser is inhibited. But, in the context of grazed pasture, to reduce the NH₃ emitted from deposited urine following each grazing event, regular applications of nBTPT are required, which would be prohibitively expensive. To mitigate NH₃ emissions from cattle urine deposited during more than a single grazing, in dairy-grazed pasture soils, it is necessary to identify alternative longer lasting inhibition approaches to using nBTPT. Therefore, the overall objective of this thesis was to assess the effectiveness and longevity of potentially longer-lasting non-specific inhibitors copper (Cu) and zinc (Zn), and the specific inhibitor N-(2-Nitrophenyl) phosphoric triamide (2-NPT) in reducing NH₃ emissions following cattle urine applied to pasture soils. The study presented in this thesis initially examined the influence of inherent and added Cu and Zn in inhibiting soil urease activity (UA), and the role of soil organic carbon (C) and soil textural and mineralogical properties on influencing the ability of these metals at inhibiting soil UA of dairy pasture soils under laboratory incubations. The study then evaluated the effect of the recently introduced UI 2-NPT on NH₃ emissions, soil microbial biomass C, pasture dry matter yield and N uptake, which was compared with the more commonly used UI nBTPT. This study involved both laboratory and field experiments. The first laboratory experiment assessed the effect of inherent and added Cu and Zn in inhibiting soil UA of dairy-grazed pasture soils. The results showed significant positive correlations between soil total C and N with soil UA for 23 soils from the Waikato region of NZ. However, there were no significant negative correlations between soil UA with inherent Cu and Zn levels. Similarly, the addition of Cu up to 20 mg kg⁻¹ soil and the combination of 5 mg Cu and 5 mg Zn kg⁻¹ soil did not significantly reduce soil UA of 4 dairy-grazed pasture soils, with contrasting organic C levels. In the second laboratory experiment, the influence of the soil C factor (soil organic C, and other related soil properties, such as clay content and cation exchange capacity (CEC)) on the effectiveness of Cu and Zn to inhibit urea hydrolysis in soil supernatants were studied. When Cu was added to 2 different soil supernatants, at rates of 5, 10, and 20 mg Cu kg⁻¹ soil, there was a significant reduction in hydrolysis of urea applied at either 120 or 600 mg urea-N kg⁻¹ soil. Additions of Zn, at a rate of 20 mg kg⁻¹ soil achieved negligible or small reductions in urea hydrolysis after either 120 or 600 mg urea-N kg⁻¹ soil applications to soil supernatants. These results suggest that Cu has a urease inhibitory effect, but its ineffectiveness in C rich pasture soils is caused by reduced bioavailability as a result of high Cu complexation. However, Zn had a negligible inhibitory effect on soil UA at the rate used in this experiment. Overall these results support the conclusion that neither metal is likely to be a practical UI for reducing NH₃ emissions from NZ dairy-grazed pasture soils. The effectiveness and longevity of 2-NPT and nBTPT in reducing NH₃ emissions from cattle urine applied to 2 dairy-grazed pasture soils were evaluated under laboratory conditions. The inhibitors were applied at the start of the experiment and urine was applied at 4 stages; (A) immediately before, (B) 29 days after, (C) 56 days after, and (D) 29 days after and again 60 days after inhibitor application, and NH₃ emissions were measured following each urine application. There were 3 application rates of 2-NPT; 0.025, 0.050, and 0.075% of total urine-N applied at Stage-A, and one rate of nBTPT; 0.025% of total urine-N applied at Stage-A. The application depth of urine applied was 10 mm for Stages A, B and C and 7.2 mm for Stage-D. The % applied urine-N that was emitted as NH₃ at the different stages ranged from 14.2 to 50.5% for the soils studied. Both UIs equally reduced total NH₃ emissions (20.6 - 27.3%), from both of the soil types, when urine was applied immediately before inhibitor application. The inhibitor 2-NPT continued to reduce emissions (5.6 - 7.4%) from urine applied up to 56 days after the inhibitor application, but only for the soil with lower microbial biomass C and UA, suggesting that 2-NPT has slightly greater longevity of efficacy than nBTPT. When urine was applied immediately before inhibitor application, inhibitors had no effect on soil microbial biomass C, measured 31 days after inhibitor application, which suggest specificity of UIs on inhibiting UA. Two field experiments were conducted during summer and autumn to assess whether the differences observed between the inhibitors 2-NPT and nBTPT in the laboratory experiment are also achieved under field conditions. In the summer experiment, the inhibitors were applied at the start of the experiment and urine was applied at 3 stages; (A) 3 hrs before, (B) 28 days after, and (C) 68 days after inhibitor application, and NH₃ emissions were measured following each urine application. The application rates of inhibitors to the urine treatments for all 3 stages were based on the percentage (0.025%) of total urine-N applied at Stage-A. In the autumn experiment, urine was only applied either immediately before or 3 hrs before inhibitor application, also at a rate of 0.025% of total urine-N. The application depth of urine applied in both of the summer and autumn experiments was 10 mm. The NH₃-N emitted in the summer experiment was between 15.3 - 23.6% of the applied urine-N (equivalent to 111 - 142 kg N ha⁻¹), however, in autumn the emissions were only 4.5% (equivalent to 27 kg N ha⁻¹ of the total N applied. In the summer experiment, only 2-NPT significantly reduced total NH3 emissions (19.5% reduction), which was only when urine was applied 28 days after the inhibitor application (Stage B). Both inhibitors significantly reduced emissions in autumn when urine was applied either 3 hrs before or immediately before inhibitor application. However, the effectiveness was greater when urine was applied immediately before inhibitor application (52.3 - 72.7% reduction) compared to urine applied 3 hrs before inhibitor application (35.0 - 41.2% reduction). The reduction was greater with 2-NPT (72.7% reduction) compared to nBTPT (52.3% reduction) when urine was applied immediately before inhibitor application. The field study confirmed the findings of laboratory study that the effectiveness and longevity of 2-NPT, in reducing NH₃ emissions from cattle urine applied to pasture soils, is greater compared to nBTPT. There was no effect of inhibitors on pasture dry matter yield and N uptake in either of the field experiments. The 2-NPT applied up to about a month prior to a grazing event in summer reduced NH3 emissions from urine patch areas at a rate equivalent to 26 kg N ha⁻¹ (based on 19.5 % reduction in summer) at the subsequent grazing. If 3 applications of 2-NPT are applied in summer (period when emissions are typically the highest) following 3 grazings that would reduce losses by 78 kg N ha⁻¹ from 3 subsequent grazings. When these reductions are extrapolated to determine the overall benefit on whole paddock basis, the total reduction in N loss (26 kg N ha⁻¹ x 3% x 3 grazings) is 2.3 kg N ha⁻¹ yr⁻¹, assuming the urine patches cover 3% of the grazed area per grazing. Thus, overall benefit from using 2-NPT is greater than nBTPT in reducing NH₃ emissions from cattle urine deposited in dairy-grazed pastures. However, the size of the reduction from using 2-NPT on whole paddock was low, compared to the amount of N cycling in grazed pastures annually. To further improve the effectiveness of inhibitors, applied after urine application in summer, future research could focus on enhancing the contact between the inhibitor and urine urea by increasing the volume of inhibitor used (>800 L ha⁻¹) and/or by implementing shorter durations (<3 hrs) between urine and inhibitor application. Further changes in volume of inhibitor applied and timing of inhibitor application should consider cost involved and feasibility in dairy farms with the current technology.Item Effect of application times of urease inhibitor (Agrotain®) on NH emissions from urine patches : a thesis presented in partial fulfilment of the requirements for the degree of Masters of Soil Science at Massey University, Manawatu, New Zealand(Massey University, 2014) Rodriguez Gelos, Maria JimenaIn grazed pastures about 80% of urine nitrogen (N) in the form of urea is rapidly hydrolysed and is subjected to ammonia (NH3) losses. The use of urease inhibitors (UI) has been used as a mitigation tool to decrease the rate of NH3 volatilization from fertilizer urea and animal urine. In previous New Zealand trials the UI effect in reducing NH3 emissions from urine has been measured by applying urine mixed with the urease inhibitor to the pasture soil thus increasing the chance to better inhibit the urease enzyme. However, these trials do not represent a realistic grazing scenario where only urine is deposited onto the soil. This current research aimed to identify the best time to spray the Agrotain® above soil pasture to reduce NH3 losses from urine patches. A field experiment was carried out on dairy farm # 4 at Massey University, Palmerston North, New Zealand. The treatments were: a control (without urine and Agrotain®), urine alone at 530 kg N ha–1 and urine plus Agrotain®. The UI was applied to the chambers and soil plots 5 and 3 days prior to urine deposition, on the same day and 1, 3 and 5 after urine deposition in autumn (April 2013). NH3 losses were measured using the dynamic chamber method. After the application of the treatments, NH3(g) volatilization was determined in the acid traps, and soil mineral N (NH4+-N and NO3--N) and pH were measured from soil plots at different times over a period of 30 days. The application of the inhibitor prior to urine deposition reduced NH3 losses with reductions of 27.6% and 17.5% achieved for UAgr-5 and UAgr-3, respectively; and there was also a reduction in both soil NH4+-N concentration and soil pH in comparison with urine alone or with the treatments where Agrotain® was applied after urine deposition. Application of Agrotain® on the same day as urine reduced NH3 losses by 9.6% but this was not statistically significant from treatments when Agrotain® was applied after urine. The application of Agrotain® after urine deposition had no effect on NH3 losses from urine.