Jagrati Singh

Decomposition of dicyandiamide (DCD) in three contrasting soils and its effect on nitrous oxide emission, soil respiratory activity, and microbial biomass—an incubation study

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 (N2O) 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 600 mg N/kg soil with 3 levels of DCD (0, 10, and 20 mg/kg). Emissions of N2O and carbon dioxide (CO2) were measured during the 58-day incubation. Simultaneously, subsamples were collected periodically from the incubating soils (40-day incubation) and the amounts of DCD, NH4+, and NO3− 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 N2O 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.

Impact of urease inhibitor on ammonia and nitrous oxide emissions from temperate pasture soil cores receiving urea fertilizer and cattle urine

New Zealands 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 (476 kg N ha(-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.

Assessment of nitrogen losses from urea and an organic manure with and without nitrification inhibitor, dicyandiamide, applied to lettuce under glasshouse conditions

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 (N2O) and ammonia (NH3) emissions, and leached to surface and ground water as nitrate (NO3–) 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/m2, respectively, and the gaseous emission of N2O and NH3 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 (NH4+) and NO3–. The results showed greater loss of N as NH3 than N2O and the effect was more pronounced in the case of urea. Addition of DCD significantly reduced N2O emissions from both urea and GG, and increased NH3 emissions from both urea and GG, with the increase being significant only for urea. Addition of DCD maintained higher soil NH4+ concentration and lower NO3– concentration than without DCD. Overall, DCD was effective in reducing N losses of N2O emissions and NO3– 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.

Quantification of reductions in ammonia emissions from fertiliser urea and animal urine in grazed pastures with urease inhibitors for agriculture inventory: New Zealand as a case study

Urea is the key nitrogen (N) fertiliser for grazed pastures, and is also present in excreted animal urine. In soil, urea hydrolyses rapidly to ammonium (NH4(+)) and may be lost as ammonia (NH3) gas. Unlike nitrous oxide (N2O), however, NH3 is not a greenhouse gas although it can act as a secondary source of N2O, and hence contribute indirectly to global warming and stratospheric ozone depletion. Various urease inhibitors (UIs) have been used over the last 30 years to reduce NH3 losses. Among these, N-(n-butyl) thiophosphoric triamide (nBTPT), sold under the trade name Agrotain®, is currently the most promising and effective when applied with urea or urine. Here we conduct a critical analysis of the published and non-published data on the effectiveness of nBTPT in reducing NH3 emission, from which adjusted values for FracGASF (fraction of total N fertiliser emitted as NH3) and FracGASM (fraction of total N from, animal manure and urine emitted as NH3) for the national agriculture greenhouse gas (GHG) inventory are recommended in order to provide accurate data for the inventory. We use New Zealand as a case study to assess and quantify the overall reduction in NH3 emission from urea and animal urine with the application of UI nBTPT. The available literature indicates that an application rate of 0.025% w/w (nBTPT per unit of N) is optimum for reducing NH3 emissions from temperate grasslands. UI-treated urine studies gave highly variable reductions (11-93%) with an average of 53% and a 95% confidence interval of 33-73%. New Zealand studies, using UI-treated urea, suggest that nBTPT (0.025% w/w) reduces NH3 emissions by 44.7%, on average, with a confidence interval of 39-50%. On this basis, a New Zealand specific value of 0.055 for FracGASF FNUI (fraction of urease inhibitor treated total fertiliser N emitted as NH3) is recommended for adoption where urea containing UI are applied as nBTPT at a rate of 0.025% w/w. Only a limited number of published data sets are available on the effectiveness of UI for reducing NH3 losses from animal urine-N deposited during grazing in a grazed pasture system. The same can be said about mixing UI with urine, rather than spraying UI before or after urine application. Since it was not possible to accurately measure the efficacy of UI in reducing NH3 emissions from animal urine-N deposited during grazing, we currently cannot recommend the adoption of a FracGASM value adjusted for the inclusion of UI.

Response of methanotrophic communities to afforestation and reforestation in New Zealand

Methanotrophs use methane (CH4) as a carbon source. They are particularly active in temperate forest soils. However, the rate of change of CH4 oxidation in soil with afforestation or reforestation is poorly understood. Here, soil CH4 oxidation was examined in New Zealand volcanic soils under regenerating native forests following burning, and in a mature native forest. Results were compared with data for pasture to pine land-use change at nearby sites. We show that following soil disturbance, as little as 47 years may be needed for development of a stable methanotrophic community similar to that in the undisturbed native forest soil. Corresponding soil CH4-oxidation rates in the regenerating forest soil have the potential to reach those of the mature forest, but climo-edaphic fators appear limiting. The observed changes in CH4-oxidation rate were directly linked to a prior shift in methanotrophic communities, which suggests microbial control of the terrestrial CH4 flux and identifies the need to account for this response to afforestation and reforestation in global prediction of CH4 emission.

Influence of dicyandiamide on nitrogen transformation and losses in cow-urine-amended soil cores from grazed pasture

In New Zealand, urine deposited by grazing animals represents the largest source of nitrogen (N) losses, as gaseous emissions of ammonia (NH3) and nitrous oxide (N2O), and leaching of nitrate (NO3-).We determined the effect of dicyandiamide (DCD) on gaseous emissions from pasture with increasing rates of urine-N application, mineral N transformations and potential leaching of N using undisturbed soil cores of Manawatu sandy loam at field capacity. The treatments included four levels of urine-N applied at 0 (control), 14.4, 29.0 and 57.0 g N/m2 with and without DCD at 2.5 g/m2. Results showed a significant (P < 0.05) increase in NH3 and N2O-N emissions as urine application was increased. The addition of DCD to corresponding urine treatments reduced N2O emissions by 33, 56 and 80%, respectively. The addition of DCD with urine to the intact soil cores at field capacity moisture content resulted in a significant increase in the soil ammonium-N (NH4+-N) concentration but little change in NH3 emissions. Addition of DCD to urine reduced potential NO3--N leaching by 60–65% but potential NH4+-N leaching increased by 2–3.5 times. There was no difference in pasture dry matter production with and without DCD treatments.

Chambers, micrometeorological measurements, and the New Zealand Denitrification–Decomposition model for nitrous oxide emission estimates from an irrigated dairy-grazed pasture

Nitrous oxide (N2O) emissions from soils are notoriously variable in space and time. Measuring and understanding variance in these emissions is imperative for improving the accuracy of the greenhouse gas inventory and assessing the viability of mitigation options; but data for N2O emissions are rather limited. Farm-scale emissions data are also required for developing and verifying predictive model estimates. A measurement campaign was undertaken from 12 October to 1 November 2006 at a highly productive grass-clover irrigated dairy farm on a stony silt loam soil in North Canterbury, South Island, New Zealand. The ∼7 ha experimental field, grazed in two morning 6-h grazing sessions (21–22 October 2006) by 718 milking dairy cattle, received two irrigations during the measurements, one before the grazing event and the other during grazing period. We first compare the emission measurements using a chamber technique against those made using a micrometeorological technique with tuneable diode-laser technology. We then compare the measured emissions against emissions predicted by a process-based model (New Zealand Denitrification–Decomposition (NZ-DNDC)). Daily averaged micrometeorological measurements gave a pre-grazing emission of 35 g N2O N/ha/day that increased to >60 g N2O N/ha/day following grazing by the dairy herd. The average pre-grazing emission of 10 g N2O N/ha/day from the chambers increased to 25 g N2O N ha−1 day−1 following grazing. The emissions were simulated with NZ-DNDC model, which gave average daily emissions of 15 ± 9 g N2O N ha−1 day−1 for the pre-grazing period and 22 ± 6 g N2O N ha−1 day−1 for the post-grazing period. Here we describe these measurement approaches, compare their emission estimates and discuss the advantages of combining them for verification of emissions.

Verification techniques for N2O emission at the paddock scale in New Zealand: FarmGas2006

High-precision micrometeorological measurement with tunable diode laser (TDL)-based trace gas analysers provides a continuous spatially integrating and non-intrusive measurement technique that is capable of detecting and quantifying episodic N2O emission at the paddock scale. Results are presented from the FarmGas2006 measurement campaign conducted on a commercial dairy farm in North Canterbury, New Zealand, over 3 weeks in October 2006. This was the first field deployment of a TDL instrument for paddock-based N2O flux measurement in New Zealand. A goal of this campaign was assessment of a range of atmospheric N2O sensing technologies and micrometeorological approaches. In this paper the capabilities of TDL technology are compared with gas chromatography (GC) in flux-gradient measurements. Baseline emission was <100 ng N/m2.s and increased to <250 ng N/m2.s following grazing by the dairy herd. There was very good correlation between GC- and TDL-determined fluxes and also good agreement between the instruments in the mean emission in 10 days before (45–50 ng N/m2.s) and after (75–80 ng N/m2.s) paddock grazing. The flux was characterised by events of high emission lasting several hours such that half of the total N2O was emitted in ~10% of the time over the duration of the campaign. We discuss the implications of this and advantages of high-precision techniques as tools for ‘top-down’ verification and for the assessment of N2O emission mitigation options.

Field-scale verification of nitrous oxide emission reduction with DCD in dairy-grazed pasture using measurements and modelling

Nitrous oxide (N2O) 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 N2O emissions from agricultural soils. In previous studies on the effect of dicyandiamide (DCD) on N2O 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 N2O 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 N2O emissions. Two circular 1260-m2 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 N2O emissions were measured periodically for 20 days. The cumulative N2O emissions were 220 ± 90 and 110 ± 20 g N2O-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 N2O 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. NZ-DNDC simulated N2O emissions of 169 and 68 g N2O-N/ha for the untreated and DCD-treated areas, respectively, corresponding to a reduction of 60% in N2O emissions from DCD application. This level of reduction is consistent with that found in experiments with individual urine patches. N2O emissions found through use of NZ-DNDC were sensitive to uncertainties in the input parameters. The combined effect of varying the initial soil NO3– and NH4+, 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 N2O emissions by –87% to +150%.

Chapter 15 The role of inhibitors in the bioavailability and mitigation of nitrogen losses in grassland ecosystems

Publisher Summary This chapter presents an overview of the sources of nitrogen (N) input to grazed grasslands, the dynamics of N in grassland soils, and environmental impacts of N losses. It discusses the role of inhibitors in improving N bioavailability and mitigating N losses. As N exists in many different inorganic and organic forms in soils and these N forms undergo several transformations, an understanding of N dynamics can help to illustrate the importance of N bioavailability and its fate in the environment. A brief summary of N inputs and dynamics in grazed pastures is presented in the chapter. The environmental impacts of N losses are outlined. The role of inhibitors in improving the N bioavailability and mitigating N losses is illustrated. A brief description is presented of the research on the use of inhibitors in New Zealand. The gaps and the limitations from the existing information are identified. The main research needs to devise mitigation strategies with inhibitors are presented.