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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 [...]

Urea and organic manures such as 'Garden galore' (GG) are used to supply nitrogen (N) in vegetable farming and floriculture systems in New Zealand. However, a significant amount of the applied N is lost to the atmosphere via nitrous oxide ([N.sub.2]O) and ammonia (N[H.sub.3]) emissions, and leached to surface and ground water as nitrate (N[O.sub.3.sup.-]) contributing to environmental degradation such as global warming and eutrophication. One of the mitigation options to reduce these losses is to use nitrification inhibitors (NI). Glasshouse and laboratory incubation experiments were conducted under controlled moisture and temperature conditions to determine the effects of an NI, dicyandiamide (DCD), on N losses from urea and GG applied to lettuce grown in a Manawatu sandy soil. Nitrogen and DCD were applied at the rates of 9 and 1.3 g/[m.sup.2], respectively, and the gaseous emission of [N.sub.2]O and N[H.sub.3] were monitored over a 5-week period using a closed-chamber technique. At the end of the experiment the lettuce plant shoots and roots were harvested, and analysed for N concentration. Soils were leached with deionised water and leachates were analysed for ammonium (N[H.sub.4.sup.+]) and N[O.sub.3.sup.-]. The results showed greater loss of N as N[H.sub.3] than [N.sub.2]O and the effect was more pronounced in the case of urea. Addition of DCD significantly reduced [N.sub.2]O emissions from both urea and GG, and increased N[H.sub.3] emissions from both urea and GG, with the increase being significant only for urea. Addition of DCD maintained higher soil N[H.sub.4.sup.+] concentration and lower N[O.sub.3.sup.-] concentration than without DCD. Overall, DCD was effective in reducing N losses of [N.sub.2]O emissions and N[O.sub.3.sup.-] leaching. Urea application resulted in shoot tip burning and the symptoms were enhanced with the addition of DCD. There was no significant effect of DCD addition on lettuce yield. Additional keywords: ammonia, DCD, Garden galore, nitrification inhibitor, nitrate leaching, nilus oxide, ammonium, nitrate., Introduction Nitrogen (N) is the major nutrient element that regulates plant growth but is also contributor to environmental degradation. In New Zealand, urea is a widely used N fertiliser and [...]

The objective of this work was to study the degradation kinetics of a nitrification inhibitor (NI), dicyandiamide (DCD), and evaluate its effectiveness in reducing nitrous oxide ([N.sub.2]O) emissions in different types of soils. Three soils contrasting in texture, mineralogy, and organic carbon (C) content were incubated alone (control) or with urine at 600mg N/kg soft with 3 levels of DCD (0, 10, and 20 mg/kg). Emissions of [N.sub.2]O and carbon dioxide (C[O.sub.2]) were measured during the 58-day incubation. Simultaneously, subsamples were collected periodically from the incubating soils (40-day incubation) and the amounts of DCD, N[H.sub.4.sup.+], and N[O.sub.3.sup.-] were determined. Our results showed that the half-life of DCD in these laboratory incubating soils at 25°C was 6-15 days and was longer at the higher rate of DCD application. Of the 3 soils studied, DCD degradation was fastest in the brown loam allophanic soil (Typic orthic allophanic) and slowest in the silt loam non-allophanic soil (Argillic-fragic Perch-gley Pallic). The differences in DCD degradation among these soils can be attributed to the differences in the adsorption of DCD and in the microbial activities of the soils. Among the 3 soils the highest reduction in [N.sub.2]O emissions with DCD from the urine application was measured in the non-allophanic silt loam soil followed by non-allophanic sandy loam soil and allophanic brown loam soil. There was no adverse impact of DCD application on soil respiratory activity or microbial biomass. Additional keywords: allophane, carbon dioxide, clay content, half-life, nitrification, organic matter., Introduction In recent decades, dicyandiamide (DCD) has been used extensively as a nitrification inhibitor (NI) because of its highly effective inhibition of nitrification, and its non-volatile and non-biocidal nature (Trenkel [...]