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New Zealand agriculture is predominantly comprised of pastoral grazing systems and deposition of animal excreta during grazing has been identified as a major source of nitrous oxide (N 2 O) emissions. Nitrification inhibitors have been shown to significantly reduce nitrous oxide emissions from grazing pastoral systems, and some plants have been identified as having nitrification inhibiting properties. Brassica crops are one such example as they contain the secondary metabolite glucosinolate (GLS) whose hydrolysis products are thought to slow soil nitrogen cycling. Forage brassicas have been increasingly used to supplement the diet of grazing animals. The aim of this study was to determine if GLS hydrolysis products (phenylethyl isothiocyanate, 4-pent-1-yl isothiocyanate, 2-propenyl nitrile, 2 propenyl isothiocyanate, 4-pentene nitrile) produced in brassica crops reduced N 2 O emissions from soil amended with urea or animal urine. In the laboratory, some GLS hydrolysis products added with urea to soil were found to decrease N 2 O emissions and the most effective product (phenylethyl isothiocyante) reduced N 2 O emissions by 51% during the study. There was some evidence that the reduction in N 2 O emissions found in the lab could be attributed to inhibition of nitrification. Results suggest that the inhibition by GLS hydrolysis products was short-lived and, if considered for use, multiple applications may be necessary to achieve effective inhibition of N 2 O emissions. This reduction, however, was not observed under field conditions. Further investigation is required to test more GLS hydrolysis products to fully understand their impact on N 2 O emissions from urine affected soil. [ABSTRACT FROM AUTHOR]

The availability of detailed input data frequently limits the application of process-based models at large scale. In this study, we produced simplified meta-models of the simulated nitrous oxide (N 2 O) emission factors (EF) using NZ-DNDC. Monte Carlo simulations were performed and the results investigated using multiple regression analysis to produce simplified meta-models of EF. These meta-models were then used to estimate direct N 2 O emissions from grazed pastures in New Zealand. New Zealand EF maps were generated using the meta-models with data from national scale soil maps. Direct emissions of N 2 O from grazed pasture were calculated by multiplying the EF map with a nitrogen (N) input map. Three meta-models were considered. Model 1 included only the soil organic carbon in the top 30 cm (SOC30), Model 2 also included a clay content factor, and Model 3 added the interaction between SOC30 and clay. The median annual national direct N 2 O emissions from grazed pastures estimated using each model (assuming model errors were purely random) were: 9.6 Gg N (Model 1), 13.6 Gg N (Model 2), and 11.9 Gg N (Model 3). These values corresponded to an average EF of 0.53%, 0.75% and 0.63% respectively, while the corresponding average EF using New Zealand national inventory values was 0.67%. If the model error can be assumed to be independent for each pixel then the 95% confidence interval for the N 2 O emissions was of the order of ± 0.4–0.7%, which is much lower than existing methods. However, spatial correlations in the model errors could invalidate this assumption. Under the extreme assumption that the model error for each pixel was identical the 95% confidence interval was approximately ± 100–200%. Therefore further work is needed to assess the degree of spatial correlation in the model errors. [ABSTRACT FROM AUTHOR]

In this study, we developed emission factor (EF) look-up tables for calculating the direct nitrous oxide (N2O) emissions from grazed pasture soils in New Zealand. Look-up tables of long-term average direct emission factors (and their associated uncertainties) were generated using multiple simulations of the NZ-DNDC model over a representative range of major soil, climate and management conditions occurring in New Zealand using 20years of climate data. These EFs were then combined with national activity data maps to estimate direct N2O emissions from grazed pasture in New Zealand using 2010 activity data. The total direct N2O emissions using look-up tables were 12.7±12.1Gg N2O–N (equivalent to using a national average EF of 0.70±0.67%). This agreed with the amount calculated using the New Zealand specific EFs (95% confidence interval 7.7–23.1Gg N2O–N), although the relative uncertainty increased. The high uncertainties in the look-up table EFs were primarily due to the high uncertainty of the soil parameters within the selected soil categories. Uncertainty analyses revealed that the uncertainty in soil parameters contributed much more to the uncertainty in N2O emissions than the inter-annual weather variability. The effect of changes to fertiliser applications was also examined and it was found that for fertiliser application rates of 0–50kg N/ha for sheep and beef and 60–240kg N/ha for dairy the modelled EF was within ±10% of the value simulated using annual fertiliser application rates of 15kg N/ha and 140kg N/ha respectively. [ABSTRACT FROM AUTHOR]

Abstract: New Zealand's intensively grazed pastures receive the majority of nitrogen (N) input in the form of urea, which is the major constituent of animal urine and the most common form of mineral N in inorganic N fertilizers. In soil, urea is rapidly hydrolyzed to ammonium (NH4 +) ions, a part of which may be lost as ammonia (NH3) and subsequently as nitrous oxide (N2O), which is a greenhouse gas. Two glasshouse experiments were conducted to study the effect of a urease inhibitor (UI), N-(n-butyl) thiophosphoric triamide (NBPT), commercially named Agrotain, applied with urine and urea on urea hydrolysis and NH3 and N2O emissions. Treatments included the commercially available products Sustain Yellow (urea+Agrotain+4% sulfur coating), Sustain Green (urea+Agrotain) and urea, and cattle urine (476kgNha−1) with and without Agrotain applied to intact soil cores of a fine sandy loam soil. The addition of Agrotain to urine and urea (i.e. Sustain Green) reduced NH3 emission by 22% to 47%, respectively. Agrotain was also effective in reducing N2O emissions from urine and Sustain Green by 62% and 48%, respectively. The reduction in N2O emissions varied with the type and amount of N applied and plant N uptake. Plant N uptake was significantly higher in the soil cores receiving Agrotain with urea than urea alone, but the slight increase in dry matter yield was non-significant. Hence, urease inhibitor reduced N losses through NH3 and N2O emissions, thereby increasing plant uptake of N. [Copyright &y& Elsevier]