Cumulative N2O Losses Research Articles

Interactive effects of soil salinity and nitrogen fertilizer types on nitrous oxide and ammonia fluxes

Soil salinization, impaired by climate change and poor management practices, poses a global threat, particularly in arid and semi-arid regions, leading to significant land degradation. This study aims to investigate the effects of different nitrogen (N) fertilizer sources (urea, ammonium-sulfate, and biogas waste) on CO2, N2O, and NH3 emissions and soil enzyme activities in two soil types varying in salinity level (non-saline: EC = 1.15 dS m−1, and saline: EC = 35.80 dS m−1) in a robotized continuous-flow soil incubation system. Our results showed a sharp increase in N2O and CO2 emissions (up to 0.51 ± 0.02 g N2O-N ha−1 day−1, 28.1 ± 3.9 kg CO2-C ha−1 day−1) in non-saline soils following soil rewetting, attributed to bacterial denitrification. However, this pattern was not observed in saline soils, suggesting that salinity causes partial inhibition to the regeneration of soil organic matter mineralization and denitrification processes after rewetting. Although salinity did not alter the overall cumulative N2O losses in any fertilizer treatment, it significantly delayed the evolution of N2O peak during the incubation period. On the other hand, NH3 volatilization was significantly higher in N-fertilized saline soils compared to non-saline soils (241% and 157% in ammonium-sulfate and biogas waste treatments, respectively), except for urea treatment, likely due to the decrease in nitrification rates. Furthermore, the study clearly showed lower soil enzyme activity levels for both nitrate reductase and urease activity. Interestingly, the lowest NH3 emissions were measured in urea treatment in both soils. Overall, our findings highlight the complex interplay between soil salinity, nitrogen fertilizer sources, and microbial processes, significantly influencing gaseous nitrogen emissions and N cycling in agricultural soils. Identifying the specific fertilizer treatments that minimize or maximize gaseous nitrogen losses in varying soil salinity, may guide the selection of appropriate fertilization strategies for farmers and policymakers to mitigate environmental impacts of fertilizer use during agricultural production.

Nitrous oxide emissions and N-cycling gene abundances in a drip-fertigated (surface versus subsurface) maize crop with different N sources

Surface drip fertigation has demonstrated promising results regarding the mitigation of nitrous oxide (N2O) emissions. The use of subsurface irrigation may offer the possibility of reducing these emissions further due to the modification of the soil moisture profile and N allocation, both of which affect the biochemical processes leading to N2O fluxes. However, the mitigation potential of subsurface irrigation combined with different mineral nitrogen (N) fertilizers (ammonium or nitrate-based, use of nitrification inhibitors) still needs to be evaluated. To respond to this need, a 2-year field experiment was set up in central Spain to test two different drip-fertigation systems (surface and subsurface at 30 cm depth) and four N fertilization treatments (control, calcium nitrate, and ammonium sulfate with or without the nitrification inhibitor 3,4-dimethylpyrazole phosphate, DMPP) in an irrigated maize (Zea mays L.) crop. Nitrous oxide emissions, mineral N concentrations (ammonium, NH4+, and nitrate, NO3−), and abundance of key N genes involved in nitrification and denitrification processes were measured in two soil layers (0–20 and 20–40 cm). Regardless of the irrigation system, ammonium sulfate gave the highest cumulative N2O losses in both campaigns, while calcium nitrate and the use of DMPP were the most effective strategies to abate N2O fluxes in the first and second years, respectively. Differences between irrigation systems were not statistically significant for cumulative N2O emissions, despite the clear effect on topsoil mineral N (higher NH4+ and NO3− concentrations in surface and subsurface drip, respectively). Nitrous oxide emissions were positively correlated with soil NH4+ concentrations. Gene abundances were not a trustworthy predictor of N2O losses in the 1st year, although a clear inhibitory effect of fertilization on microbial communities (i.e., ammonia oxidizers, nitrite reducers, and N2O reducers) was observed during this campaign. During the second year, nitrifying and denitrifying genes were affected by irrigation (with higher abundances in the 20–40 cm layer in subsurface than in surface drip) and by the addition of DMPP (which had a detrimental effect on gene abundances in both irrigation systems that disappeared after the fertigation period). In conclusion, the use of DMPP or calcium nitrate instead of ammonium sulfate may enhance the chances for an additional mitigation in both surface and subsurface irrigation systems.

Using DMPP with cattle manure can mitigate yield-scaled global warming potential under low rainfall conditions

Organic fertilisers can reduce the carbon (C) footprint from croplands, but adequate management strategies such as the use of nitrification inhibitors are required to minimise side-effects on nitrogen (N) losses to the atmosphere or waterbodies. This could be particularly important in a context on changing rainfall patterns due to climate change. A lysimeter experiment with maize (Zea mays L.) was set up on a coarse sandy soil to evaluate the efficacy of 3,4-dimethylpyrazole phosphate (DMPP) to mitigate nitrous oxide (N2O) emissions, nitrate (NO3−) leaching losses and net global warming potential from manure, with (R+) and without (R-) simulated rainfall events. Soil water availability was a limiting factor for plant growth and microbial processes due to low rainfall during the growing season. Nitrification was effectively inhibited by DMPP, decreasing topsoil NO3− concentrations by 28% on average and cumulative N2O losses by 82%. Most of the N2O was emitted during the growing season, with annual emission factors of 0.07% and 0.95% for manure with and without DMPP, respectively. Cumulative N2O emissions were 40% higher in R-compared to R+, possibly because of the higher topsoil NO3− concentrations. There was no effect of DMPP or rainfall amount on annual NO3− leaching losses, which corresponded to 12% of manure-N and were mainly driven by the post-harvest period. DMPP did not affect yield or N use efficiency (NUE) while R-caused severe reductions on biomass and NUE. We conclude that dry growing seasons can jeopardize crop production while concurrently increasing greenhouse gas emissions from a sandy soil. The use of nitrification inhibitors is strongly recommended under these conditions to address the climate change impacts.

Untangling soil‐weather drivers of daily N2O emissions and fertilizer management mitigation strategies in no‐till corn

AbstractFertilizer N management can mitigate N2O emissions but complex soil‐weather conditions modulate the mitigation potential. Conditional inference tree (CIT) is a machine learning method able to untangle complex interactions while providing an interpretable model. The goals of this study were (a) to assess the effect of N fertilizer on N2O emissions, and to use CIT to identify (b) the main soil‐weather drivers of daily N2O hot moments and (c) fertilizer management options to mitigate them. The study was conducted in 2 yr in no‐till corn (Zea mays L.) with seven combinations of N source and placement tested. Daily N2O emissions were measured with vented chambers, and soil temperature and water‐filled pore space (WFPS) were measured near the chambers on the same days of gas sampling. Overall, 2013 was drier with lower N2O emissions than 2014. Cumulative N2O losses differed across treatments and years, with broadcast emitting more in 2014 than in 2013, and only subsurface‐banded fertilizer with a nitrification inhibitor (NI) consistently abated N2O losses. The main hot moment conditions were within ∼80 d of fertilizer application when soil temperature >15 °C and WFPS >57%. Under these conditions, NI abated losses by 50% compared with fertilizer alone. The machine learning approach used here could be used in larger datasets to elucidate environment‐specific drivers of N2O hot moments and potential fertilizer mitigation practices under different soil, weather, and management conditions.

Greenhouse gas emissions from an irrigated cropping rotation with dairy manure utilization in a semiarid climate

AbstractThis long‐term study was established to increase knowledge of greenhouse gas (GHG) emissions from irrigated cropping systems utilizing dairy manure solids and compost in semiarid southern Idaho. The objective of this field study was to determine the effect of synthetic N fertilizer (urea or SuperU [enhanced‐efficiency synthetic fertilizer]), composted dairy manure, dairy manure (fall or spring applied), and a control (no fertilizer or manure) on nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) emissions over the growing season. The fertilizer and manure treatments were not applied to alfalfa (Medicago sativa L.) (2017) but were applied to corn (Zea mays L.) (2018; except SuperU) and barley (Hordeum vulgare L.) (2019). Cumulative N2O losses over the 3 yr ranged from 2.8 to 5.2 kg N2O‐N ha–1, with the fall and spring manure emitting the greatest amounts of N2O. Emission factors indicated that up to 0.79% of the total N applied was lost as N2O‐N during the growing seasons. Cumulative losses of CO2 and CH4 across the rotation were on average 12,170 kg CO2–C ha–1 and –0.77 kg CH4–C ha–1, respectively, with no significant differences among the treatments. Major N2O pulses were associated with early‐season irrigation events and incorporation of fertilizer and manure, but overall fluxes tended to be the greatest when soil temperatures were higher. Dairy manure and compost applications were also found to cause rapid and significant increases in soil organic carbon (SOC) in the top 30 cm of soil under corn and barley. Despite the fact that manure does cause elevated soil N2O emissions, it should be considered as an alternative to synthetic fertilizer use due to its ability to increase SOC and potentially help reduce the global warming potential.

Nitrogen dynamics under corn fields in the Red River Valley of North Dakota

AbstractExcessive applications of fertilizer N in corn (Zea mays L.) has profound environmental and economic consequences. Corn grain yield, N losses, N2O denitrification, NH3 volatilization, and soil water NO3 concentration at 60‐cm depth were collected for eight corn fields in the Red River Valley of North Dakota. Relationships of soil and management factors with cumulative N2O and NH3 losses were studied. Grain yield varied from 3.58 to 5.66 Mg ha–1. Cumulative NH3 and N2O losses were ranged between 1.0–2.4 kg ha–1 and 24.7–150 g N2O‐N ha–1, respectively. Soil organic matter (SOM; r = .94, p = .001), clay (r = .94, p = .001), and initial inorganic N (0–60 cm) content (r = .83, p = .01) had a positive relationship with cumulative N2O losses. Cumulative NH3 had a negative relationship with soil pH (r2 = .63, p = .01). Results indicate that soil properties such as, SOM, clay concentration, and initial profile N had a control over N losses.

Joint mitigation of NH3 and N2O emissions by using two synthetic inhibitors in an irrigated cropping soil

Ammonia (NH3) emissions from cropping systems are a major pathway of nitrogen (N) loss thus strongly affecting nitrogen use efficiency (NUE). The agriculture sector is responsible for ca. 94% of global NH3 emissions, mostly associated with manure management (56%), animal manure applied to soil (18%) and inorganic N fertilization (21%). Furthermore, N fertilization enhances N2O emissions from cropping systems. The assessment of NH3, and also N2O, abatement strategies on a regional basis has, therefore, become a strategic priority for sustainable food production worldwide.A field experiment, under Mediterranean conditions, was carried out to assess the N2O and NH3 mitigation efficiency of different synthetic inhibitors in an irrigated maize crop fertilized with urea (U). The nitrification inhibitor (NI) 3,4 dimethylpyrazole succinic acid (DMPSA), and the combination of the DMPSA and the urease inhibitor (UI), N-(n-butyl) thiophosphoric triamide (NBPT), were used in the experiment. Our findings indicate that, following top-dressing N fertilization, the highest NH3 emissions were observed after U + NI and U applications (12.2 and 11.1 kg N ha−1, respectively), with no significant differences between them. The application of urea with both inhibitors (U + 2I) significantly reduced these emissions down to 3.3 kg N ha−1. During canopy senescence, NH3 emissions were not negligible and were statistically similar between treatments, with an average value of 2.3 kg N ha−1. In addition, the treatments with NI were effective in reducing cumulative N2O losses (ca. 79%).

Advanced Processing of Food Waste Based Digestate for Mitigating Nitrogen Losses in a Winter Wheat Crop

The anaerobic digestion of food waste converts waste products into ‘green’ energy. Additionally, the secondary product from this process is a nutrient-rich digestate, which could provide a viable alternative to synthetically-produced fertilisers. However, like fertilisers, digestate applied to agricultural land can be susceptible to both ammonia (NH3) and nitrous oxide (N2O) losses, having negative environmental impacts, and reducing the amount of N available for crop uptake. Our main aim was to assess potential methods for mitigating N losses from digestate applied to a winter wheat crop and subsequent impact on yield. Plot trials experiments were conducted at two UK sites, England (North Wyke-NW) and Wales (Henfaes-HF), to assess NH3 and N2O losses, yield and N offtake following a single band-spread digestate application. Treatments examined were digestate (D), acidified-digestate (AD), digestate with the nitrification inhibitor DMPP (D+NI), AD with DMPP (AD+NI), and a zero-N control (C). Determination of N losses was conducted using wind tunnels for NH3, and static manual and automatic chambers for N2O. The N offtake in both grain and straw was also measured. Ammonium nitrate (NH4NO3) fertiliser N response plots (from 75 to 300 kg N ha−1) were included to compare yields with the organic N source. Across both sites, cCumulative NH3-N losses were 27.6 % from D and D+NI plots and 1.5 % for AD and AD+NI of the total N applied, a significant reduction of 95 % with acidification. Cumulative N2O losses, varied between 0.13 and 0.35 % of the total N applied and were reduced by 50 % with the use of DMPP although the differences were not significant. Grain yields for the digestate treatments were 7.52 – 9.21 and 7.23 – 9.23 t DM ha−1 at HF and NW, respectively. Yields were greater from the plots receiving acidified-digestate relative to the non-acidified treatments but the differences were not significant. The yields (as a function of the N applied with each treatment) obtained for the digestate treatments ranged between 84.2 % (D+NI) and 103.6 % (D) of the yields produced by the same N rate from an inorganic source at HF. Advanced processing of digestate

The effect of nitrification inhibitors on NH3 and N2O emissions in highly N fertilized irrigated Mediterranean cropping systems

There is an increasing concern about the negative impacts associated to the release of reactive nitrogen (N) from highly fertilized agro-ecosystems. Ammonia (NH3) and nitrous oxide (N2O) are harmful N pollutants that may contribute both directly and indirectly to global warming. Surface applied manure, urea and ammonium (NH4+) based fertilizers are important anthropogenic sources of these emissions. Nitrification inhibitors (NIs) have been proposed as a useful technological approach to reduce N2O emission although they can lead to large NH3 losses due to increasing NH4+ pool in soils. In this context, a field experiment was carried out in a maize field with aiming to simultaneously quantify NH3 volatilization and N2O emission, assessing the effect of two NIs 3,4‑dimethilpyrazol phosphate (DMPP) and 3,4‑dimethylpyrazole succinic acid (DMPSA). The first treatment was pig slurry (PS) before seeding (50 kg N ha−1) and calcium ammonium nitrate (CAN) at top-dressing (150 kg N ha−1), and the second was DMPP diluted in PS (PS + DMPP) (50 kg N ha−1) and CAN + DMPSA (150 kg N ha−1) also before seeding and at top-dressing, respectively. Ammonia emissions were quantified by a micrometeorological method during 20 days after fertilization and N2O emissions were assessed using manual static chambers during all crop period. The treatment with NIs was effective in reducing c. 30% cumulative N2O losses. However, considering only direct N2O emissions after second fertilization event, a significant reduction was not observed using CAN+DMPSA, probably because high WFPS of soil, driven by irrigation, favored denitrification. Cumulative NH3 losses were not significantly affected by NIs. Indeed, NH3 volatilization accounted 14% and 10% of N applied in PS + DMPP and PS plots, respectively and c. 2% of total N applied in CAN+DMPSA and CAN plots. Since important NH3 losses still exist even although abating strategies are implemented, structural and political initiatives are needed to face this issue.

Zinc fertilizers influence greenhouse gas emissions and nitrifying and denitrifying communities in a non-irrigated arable cropland

Fertilization with micronutrients (e.g., zinc, Zn) is essential in order to overcome the global nutritional problems associated with human micronutrient deficiencies. However, little is known about the effect of micronutrient fertilizers and their interaction with nitrogen (N) on greenhouse gas (GHG) emissions and soil microbial processes involved in nitrous oxide (N2O) fluxes. In this context, a one-year field experiment was carried out using a winter wheat (Triticum aestivum L.) crop in Central Spain. Winter wheat was treated with different Zn sources (Zn-sulphate, Zn-lignosulphonate, Zn with a mixture of synthetic chelating compounds DTPA-HEDTA-EDTA and Zn-humic/fulvic acids) and N rates (0, 120 and 180 kg N ha−1). Zn sources were applied at 10 kg Zn ha−1 for Zn-sulphate and 0.36 kg Zn ha−1 for the rest of treatments. Nitrous oxide, methane (CH4) and respiration fluxes were measured (two-three times per week during the first month after each fertilization and thereafter with decreasing frequency), as were the total abundances of soil Bacteria and Archaea, ammonia-oxidizing Bacteria and Archaea, and denitrifying bacteria. The DTPA-HEDTA-EDTA reduced cumulative N2O losses by 21.4% and respiration fluxes by 24.4% from those of the no Zn application. The chelating of metal co-factors (mainly copper, Cu) of the enzymes involved in the nitrification and denitrification steps was the probable mechanism for the reduction of N2O emissions as bacterial amoA, nirK, nirS and norB gene abundances, as well as the extractable Cu content, decreased in this treatment. Unexpectedly, the DTPA-HEDTA-EDTA increased the copy number of nosZ by 31.2% over that of the no Zn application. The Zn applied together with the humic/fulvic acids mixture caused significant increases of total bacterial abundance and nitrifier and denitrifier communities, particularly the norB gene, thereby leading to the highest N2O emissions. The optimum N rate was 120 kg N ha−1 since it resulted in the lowest yield-scaled N2O losses and N surplus. The application of synthetic Zn chelates can be recommended as a win-win mitigation and adaptation strategy aimed at reducing yield-scaled GHG emissions and at the enhancement of Zn biofortification.

Nitrous oxide emissions from cattle urine deposited onto soil supporting a winter forage kale crop

ABSTRACTWintering cows on forage crops leads to urine being excreted onto wet, compacted soils, which can result in significant emissions of nitrous oxide (N2O). A field trial was conducted to determine the N2O emission factor (EF3; proportion of urine-N lost as N2O-N) for dairy cows wintered on a kale forage crop on a poorly drained soil. Urine was collected from non-lactating dairy cows on a forage kale diet and applied at 550 kg N ha−1 to artificially compacted soil to simulate trampling and non-compacted soil in a kale field. Cumulative N2O losses over four months were 7.38 and 2.64 kg N2O-N ha−1 from urine applied to, respectively, compacted and non-compacted soil. The corresponding EF3 values 0.75% and 0.30%, respectively, differed (P = .003) due to compaction. Combining our results with previous studies, where brassica-fed livestock urine was applied to soils supporting a forage brassica crop, suggested a significant relationship between soil water-filled pore space (WFPS) and brassica-derived urine EF3 (P = .005).

Effects of N placement, carbon distribution and temperature on N2O emissions in clay loam and loamy sand soils

AbstractChanges in the profile distribution of soil C stocks for conventional versus no‐tillage can affect N2O losses. Uncertainty remains whether deep N placement into a wetter layer in humid areas would affect N2O losses. This study evaluated the effects of soil carbon profile distribution (inverted, normal), depth of nitrogen placement (5 cm, 15 cm), temperature (10, 20 and 30 °C) and soil texture (clay loam, loamy sand) on N2O emissions from soil cores in a 216‐h incubation after simulated rainfall. N2O losses were larger from the clay loam than from the loamy sand, and cumulative N2O emissions from the inverted profile, with greater C levels at depth, were more than those from the profile with more C near the upper surface. Cumulative N2O losses from the inverted clay loam profile with deep N placement (1.16 mg N per kg dry soil; 0.71% of applied N) on average were almost double those in the loamy sand (0.62 mg N per kg dry soil; 0.42%). The smallest N2O losses were measured from the profiles with more C close to the upper surface with a shallow placement of N for the clay loam (0.19 mg N per kg dry soil; 0.12%) and loamy sand (0.33 mg N per kg dry soil; 0.23%). An exponential relationship between N2O fluxes and temperature was measured. We conclude that large N2O losses may occur under the combination of greater soil C content at deeper layers (ploughed soils) and moist profiles after N application (humid regions). Deep N placement appears to aggravate rather than ameliorate these concerns.

Using near-continuous measurements of N2O emission from urine-affected soil to guide manual gas sampling regimes

Nitrous oxide (N2O) fluxes are influenced by fluctuating soil temperature and external factors such as rainfall events. Therefore, sampling time, frequency of sampling after nitrogen (N) application and weather interactions are critical when determining cumulative N2O losses and associated emission factors. Using automated chambers, three short-term field trials were conducted to measure N2O fluxes from urine-affected pasture in southern New Zealand to determine the influence of soil temperature and light on diurnal N2O variation and the effect of sampling frequency on estimated cumulative N2O losses. Diurnal N2O flux patterns were often interrupted by rainfall events, but when present they were mainly driven by fluctuations in soil temperature at 0–2 cm depth. Mean daily N2O fluxes occurred between 10:00–12:00 h and 18:00–21:00 h. Analysis of all data, including rainfall-affected periods, showed that gas sample collection three times a week between 10:00–12:00 h provided zero bias in calculated cumulative emissions when compared with those based on frequent, 2-hourly, flux measurements. To account for resource limitations in field campaigns for estimating cumulative N2O emissions, an alternative approach is to sample two times a week, when fluxes can be expected to be large (e.g. first 4–6 weeks following urine deposition on to pasture), with additional sampling following significant rainfall. This latter approach produced an average bias of +4%, but ranged from −3 to +18%.

Influence of Urea Fertilizer Placement on Nitrous Oxide Production from a Silt Loam Soil

Urea placement in band or nests has been shown to enhance N use efficiency, but limited work has been done to assess its affect on N(2)O emissions. This study compared N(2)O emissions from urea prills applied to an Amsterdam silt loam (fine-silty, mixed, superactive, frigid Typic Haplustolls) using broadcast, band, and nest placements. Experiments were conducted in greenhouse pots (200 kg N ha(-1)) and in canola (Brassica rapa L.) seeded fields using rates of 100 kg N ha(-1) (recommended) and 200 kg N ha(-1). Urea placement affected N(2)O emission patterns and cumulative N(2)O losses in the greenhouse and field. Urea prills placed in nests, and sometimes bands delayed N(2)O production with peak flux activity occurring later, and elevated emission activity being more prolonged than for broadcast applications. Differences were more obvious at 200 kg N ha(-1). These effects were attributed to a delay in urea hydrolysis and inhibition of nitrification. The fraction of applied urea-N lost as N(2)O for broadcast, band, and nest placements applied at the recommended rate averaged 2.0, 2.7, and 5.8 g N kg(-1) N, respectively. The fraction of applied urea-N lost as N(2)O averaged 2.9, 10.4, and 9.2 g N kg(-1) N for broadcast, band, and nest placements when urea-N rate was increased from 100 to 200 kg N ha(-1), respectively. Greater N(2)O production with nest placement may in part be due to significant soil NO(2)-N accumulations. Potential benefits to crop fertilizer use efficiency that come with placement of urea in concentrated zones may lead to enhanced N(2)O production.

Nitrous oxide emissions and soil mineral nitrogen status following application of hog slurry and inorganic fertilisers to acidic soils under forage grass

Field application of livestock slurry often results in higher nitrous oxide (N2O) emissions than inorganic fertiliser, because slurry contains large amounts of available N and C, and when applied it increases soil water content, thus enhancing denitrification. This study evaluated the impact of hog (Sus scrofa) slurry and inorganic fertilisers on N2O emissions and soil inorganic N. Three short-term (3 wk) field experiments were conducted during summer 2005 on two contrasting acidic soils seeded to forage grass. Treatments included hog slurry (Slurry) at 126 kg N ha-1, potassium nitrate (Nitrate) at 120 kg N ha-1, ammonium sulphate (Ammonium) at 120 kg N ha-1, Carbon (Dextrose) at 500 kg ha-1 and an unamended control (Control). Potassium nitrate increased (P< 0.05) cumulative N2O losses compared with the other treatments. Emissions of N2O from Slurry and Ammonium were similar, but higher than from Dextrose and Control, which were similar. Soil NH4+-N contents for Slurry and Ammonium treatments were generally similar but higher than for the other treatments, particularly during the first and second sampling dates. Soil NO3−-N contents, meanwhile, were higher with the Nitrate treatment compared with the other treatments, especially at the first sampling date. These results imply that N2O production in these acid soils was limited by NO3-availability. Therefore, N2O emissions from these soils can be minimised by using ammonium-based fertilisers including hog slurry rather than nitrate-based fertilisers. Key words: Acidic soils, hog slurry, mineral fertiliser, soil nitrogen, N2O emissions

3, 4‐Dimethylpyrazole phosphate reduces nitrous oxide emissions from grassland after slurry application

Abstract. A field study was conducted to assess the effect of the nitrification inhibitor 3,4‐dimethylpyrazole phosphate (DMPP), applied at a rate of 1 kg ha−1, on nitrous oxide (N2O) emissions, forage production and N extraction from a grassland soil after cattle slurry applications in autumn and spring. Nitrous oxide emissions were measured daily or weekly using the closed chamber technique. DMPP efficiency after slurry application was lower in spring (16.7 °C mean soil temperature) than in autumn (11.4 °C mean soil temperature). Thus, DMPP was able to maintain soil mineral N in the ammonium form for 22 days and reduce cumulative N2O emissions by 69% in autumn, while in spring its effect on soil mineral N lasted for 7–14 days, reducing cumulative N2O losses by 48%. Furthermore, application of DMPP after slurry did not decrease biomass yield or N uptake.

Nitrous oxide flux from nitric-acid-treated cattle slurry applied to grassland under semi-controlled conditions

Nitrous oxide (N2O) fluxes from cattle slurry after surface application to grassland were measured under semi-controlled environmental conditions during three periods in 1991. Three types of cattle slurry were examined; untreated slurry and slurries treated with nitric acid (HNO3) to pH 6.0 and 4.5. Treatment with HNO3 is a proposed technique to reduce ammonia volatilization from slurry during storage, and during and after surface application. N2O flux was determined one to four times a day for 7 to 18 days after application of 0.64 to 3.8 kg slurry/msuperscript 2. Slurry-derived fluxes were greater from treated slurries than from untreated slurries. Cumulative N2O losses ranged from