Nitrous oxide emissions from grassland and spring barley, following N fertiliser application with and without nitrification inhibitors

The aims of this study were to assess the effectiveness of the nitrification inhibitors dicyandiamide (DCD) and nitrapyrin on reducing emissions of nitrous oxide (N₂O) following application of NH₄ ⁺ or NH₄ ⁺-forming fertilisers to grassland and spring barley. DCD was applied to grassland with N fertiliser applications in April and August in 1992 and 1993, inhibiting N₂O emissions by varying amounts depending on the fertiliser form and the time of application. Over periods of up to 2 months following each application of DCD, emissions of N₂O were reduced by 58–78% when applied with urea (U) and 41–65% when applied with ammonium sulphate (AS). Annual emissions (April to March) of N₂O were reduced by up to 58% and 56% in 1992–1993 and 1993–1994, respectively. Applying DCD to ammonium nitrate (AN) fertilised grassland did not reduce emissions after the April 1993 fertilisation, but emissions following the August application were reduced. Nitrapyrin was only applied once, with the April fertiliser applications in 1992, reducing N₂O emissions over the following 12 months by up to 40% when applied with U. When N fertiliser was applied in June without DCD, the DCD applied in April was still partly effective; N₂O emissions were reduced 50%, 60% and 80% as effectively as the emissions following the April applications, for AS in 1993, U in 1992 and 1993, respectively. In 1992 the persistence of an inhibitory effect was greater for nitrapyrin than for DCD, increasing after the June fertiliser application as overall emissions from U increased. There was no apparent reduction in effectiveness following repeated applications of DCD over the 2 years. N₂O emissions from spring barley, measured only in 1993, were lower than from grassland. DCD reduced emissions from applied U by 40% but there was no reduction with AN. The results demonstrate considerable scope for reducing emissions by applying nitrification inhibitors with NH₄ ⁺ or NH₄ ⁺-forming fertilisers; this is especially so for crops such as intensively managed grass where there are several applications of fertiliser nitrogen per season, as the effect of inhibitors applied in April persists until after a second fertiliser application in June. Received: 30 August 1996     

Nitrous oxide emissions from grassland in an intensive dairy farm in the Basque Country of Spain

Abstract. Intensively managed grasslands are potentially a large source of N₂O in the North Coast of Spain because of the large N input, the wet soil conditions and mild temperatures. To quantify the effect of fertilizer type and management practices carried out by farmers in this area, field N₂O losses were measured over a year using the closed chamber technique. Plots received two types of fertilizer: cattle slurry (536 kg N ha^–1) and calcium ammonium nitrate (140 kg N ha^–1). N₂O losses were less in the slurry treatment than after mineral fertilizer. This was probably due to high, short‐lived peaks of N₂O encountered immediately following mineral N addition. In contrast, the seasonal distribution of N₂O losses from the slurry amended plot was more uniform over the year. The greater N₂O losses in the mineral treatment might have been enhanced by the combined effect of mineral fertilizer and past organic residues present from previous organic amendments. Weak relationships were found between N₂O emission rates and soil nitrate, soil ammonium, soil water content and temperature. Better relationships were obtained in the mineral treatment than in the slurry plots, because of the wider range in soil mineral N. Water filled pore space (WFPS) was a key factor controlling N₂O emissions. In the > 90% WFPS range no relationships were found. The best regressions were found for the mineral treatment in the 40–65% WFPS range, 49% of the variance being explained by soil nitrate and ammonium content. In the 65–90% WFPS range, 43% of the variance was explained by nitrate only, but the inclusion of soil ammonium did not improve the model as it did in the 40–65% WFPS range. This fact indicates that nitrification is likely to be an important process involved in N₂O emissions at the 40–65% WFPS.     

Nitrous oxide emissions from animal urine application on a New Zealand pasture

Animal excreta-nitrogen (N) deposited onto pastoral soils during grazing has been identified as an important source of nitrous oxide (N₂O). Understanding the extent and seasonal variation of N₂O emissions from animal urine is important for the development of best management practices for reducing N₂O losses. The aim of this study was to determine N₂O emissions from cow urine after application onto a pastoral soil in different seasons between 2003 and 2005. A closed soil chamber technique was used to measure the N₂O emissions from a poorly drained silt loam soil which received either 0 (control) or 1,000 kg N ha⁻¹ (as real cow urine) per application. Application of cow urine to soil increased N₂O fluxes above those from the control site for up to 6 weeks, but the duration for which N₂O levels were elevated depended on the season. Nitrous oxide emissions were higher during the winter and spring measurement periods when the soil water-filled pore space (WFPS) was mostly above field capacity, and the emissions were lower during the summer and autumn measurement periods when the soil WFPS was below field capacity. The N₂O emission factor for urine ranged from 0.02 to 1.52% of N applied. This seasonal effect suggests that a reduction in urine return to soil (e.g., through use of standoff pads or animal housing) under wet conditions in New Zealand can potentially reduce N₂O emissions from pastoral soils.     

Snow cover and soil moisture controls of freeze–thaw-related soil gas fluxes from a typical semi-arid grassland soil: a laboratory experiment

In situ field measurements as well as targeted laboratory studies have shown that freeze–thaw cycles (FTCs) affect soil trace gas fluxes. However, most of past laboratory studies adjusted soil moisture before soil freezing, thereby neglecting that snow cover or water from melting snow may modify effects of FTCs on soil trace gas fluxes. In the present laboratory study with a typical semi-arid grassland soil, three different soil moisture levels (32 %, 41 %, and 50 % WFPS) were established (a) prior to soil freezing or (b) by adding fresh snow to the soil surface after freezing to simulate field conditions and the effect of the melting snow on CO₂, CH₄, and N₂O fluxes during FTCs more realistically. Our results showed that adjusting soil moisture by watering before soil freezing resulted in significantly different cumulative fluxes of CH₄, CO₂, and N₂O throughout three FTCs as compared to the snow cover treatment, especially at a relatively high soil moisture level of 50 % WFPS. An increase of N₂O emissions was observed during thawing for both treatments. However, in the watering treatment, this increase was highest in the first thawing cycle and decreased in successive cycles, while in the snow cover treatment, a repetition of the FTCs resulted in a further increase of N₂O emissions. These differences might be partly due to the different soil water dynamics during FTCs in the two treatments. CO₂ emissions were a function of soil moisture, with emissions being largest at 50 % WFPS and smallest at 32 % WFPS. The largest N₂O emissions were observed at WFPS values around 50 %, whereas there were only small or negligible N₂O emissions from soil with relatively low soil water content, which indicates that a threshold value of soil moisture might exist that triggers N₂O peaks during thawing.     

Influence of Watering Methods on the Short-Term Pulse Emissions of Nitrous Oxide from Disturbed Horticultural Soil

To reveal the impact of soil disturbance and surface watering (SW) following soil disturbance on the pulse nitrous oxide (N₂O) emissions, incubated experiments were conducted on disturbed soil with two watering regimes [surface watering only (SWO) and subsurface watering followed by surface watering (SUW+SW)]. Intensive soil disturbance led to pulses N₂O emissions from SUW + SW soil (>8,693 μg N₂O m^?2 h^?1 with a peak of 30,938 μg N₂O m^?2 h^?1), although the water-filled pore space (WFPS) was substantially lower than the previously reported optimal soil moisture range (45–75% WFPS) for peak N₂O emissions. N₂O emissions from the disturbed soil after SW were much lower than those from SUW + SW soil, increased as the soil dried, and peaked when the WFPS fell within the optimal soil moisture range. These peaks were considerably less than those resulting from the intensive disturbance in SUW + SW soil. Thus, SW after intensive soil disturbance may be effective for mitigating of pulse N₂O emissions caused by soil disturbance.     

Nitrous oxide emission from a transplanted rice field in alluvial soil as influenced by management of nitrogen fertiliser

We investigated nitrous oxide (N₂O) emission from an irrigated rice field over two years to evaluate the management of nitrogenous fertiliser and its effect on reducing emissions. Four forms of nitrogenous fertilisers: NPK at the recommended application rate, starch–urea matrix (SUM) + PK, neem‐coated urea + PK and urea alone (urea without coating) were used. Gas samples were collected from the field at weekly intervals with the static chamber technique. N₂O emissions from different treatments ranged from 11.58 to 215.81 N₂O‐N μg/m²/h, and seasonal N₂O emissions from 2.83 to 3.89 kg N₂O‐N/ha. Compared with other fertilisers, N₂O emissions were greatest after the application of the conventional NPK fertiliser. Moreover, SUM + PK reduced total N₂O emissions by 22.33% (P < 0.05) compared with NPK during the rice‐growing period (P < 0.05). The results indicate a strong correlation between N₂O emissions and soil organic carbon, nitrate, ammonium, above‐ and below‐ground plant biomass and photosynthesis (P < 0.05). The application of SUM + PK in rice fields is suitable as a means of reducing N₂O emissions without affecting grain production.     

The effects of temperature, water-filled pore space and land use on N2O emissions from an imperfectly drained gleysol

To investigate the effect of soil physical conditions and land use on emissions of nitrous oxide (N₂O) to the atmosphere, soil cores of an imperfectly drained gleysol were taken from adjacent fields under perennial ryegrass and winter wheat. The cores were fertilized with ammonium nitrate and incubated at three different temperatures and water‐filled pore space (WFPS) values, and N₂O emissions were measured by gas chromatography. Emissions showed a very large response to temperature. Apparent values of Q₁₀ (emission rate at (T + 10)°C/emission rate at T°C) for the arable soil were about 50 for the 5–12°C interval and 8.9 for 12–18°C; the corresponding Q₁₀s for the grassland soil were 3.7 and 2.3. Emissions from the grassland soil were always greater than those from the arable soil, although the ratio narrowed with increasing temperature. Changes in soil WFPS also had a profound effect on emissions. Those from the arable soil increased about 30‐fold as the WFPS increased from 60 to 80%, while that from the grassland soil increased 12‐fold. This latter response was similar to earlier field measurements. The N₂O emissions were considered to be produced primarily by denitrification. We concluded that the impacts of temperature and WFPS on emissions could both be explained on the basis of existing models relating increasing respiration or decreased oxygen diffusivity, or both, to the development of anaerobic zones within the soil.     

Emissions of N2O from soils during cycles of freezing and thawing and the effects of soil water, texture and duration of freezing

Freezing and thawing influence many physical, chemical and biological processes in soils, including the production of trace gases. We studied the effects of freezing and thawing on three soils, one sandy, one silty and one loamy, on the emissions of N₂O and CO₂. We also studied the effect of varying the water content, expressed as the percentage of the water‐filled pore space (WFPS). Emissions of N₂O during thawing decreased in the order 64% > 55% > 42% WFPS, which suggests that the retardation of the denitrification was more pronounced than the acceleration of the nitrification with increasing oxygen concentration in the soil. However, emissions of N₂O at 76% WFPS were less than at 55% WFPS, which might be caused by an increased ratio of N₂/N₂O in the very moist conditions. The emission of CO₂ was related to the soil water, with the smallest emissions at 76% WFPS and largest at 42% WFPS. The emissions of CO₂ during thawing exceeded the initial CO₂ emissions before the soils were frozen, which suggests that the supply of nutrients was increased by freezing. Differences in soil texture had no marked effect on the N₂O emissions during thawing. The duration of freezing, however, did affect the emissions from all three soils. Freezing the soil for less than 1 day had negligible effects, but freezing for longer caused concomitant increases in emissions. Evidently the duration of freezing and soil water content have important effects on the emission of N₂O, whereas the effects of texture in the range we studied were small.     

Soil N<Subscript>2</Subscript>O emissions and N<Subscript>2</Subscript>O/(N<Subscript>2</Subscript>O+N<Subscript>2</Subscript>) ratio as affected by different fertilization practices and soil moisture

The objective of this work was to evaluate the effect of the chemical nature and application frequency of N fertilizers at different moisture contents on soil N₂O emissions and N₂O/(N₂O+N₂) ratio. The research was based on five fertilization treatments: unfertilized control, a single application of 80 kg ha⁻¹ N-urea, five split applications of 16 kg ha⁻¹ N-urea, a single application of 80 kg ha⁻¹ N–KNO₃, five split applications of 16 kg ha⁻¹ N–KNO₃. Cumulative N₂O emissions for 22 days were unaffected by fertilization treatments at 32% water-filled pore space (WFPS). At 100% and 120% WFPS, cumulative N₂O emissions were highest from soil fertilized with KNO₃. The split application of N fertilizers decreased N₂O emissions compared to a single initial application only when KNO₃ was applied to a saturated soil, at 100% WFPS. Emissions of N₂O were very low after the application of urea, similar to those found at unfertilized soil. Average N₂O/(N₂O+N₂) ratio values were significantly affected by moisture levels (p = 0.015), being the lowest at 120% WFPS. The N₂O/(N₂O+N₂) ratio averaged 0.2 in unfertilized soil and 0.5 in fertilized soil, although these differences were not statistically significant.     

Processes responsible for the nitrous oxide emission from a Costa Rican Andosol under a coffee agroforestry plantation

We used the inhibitor acetylene (C₂H₂) at partial pressures of 10 Pa and 10 kPa to inhibit autotrophic nitrification and the reduction of nitrous oxide (N₂O) to N₂, respectively. Soils (Andosol) from a Coffea arabica plantation shaded by Inga densiflora in Costa Rica were adjusted to 39, 58, 76 and 87% water-filled pore space (WFPS) and incubated for 6 days in the absence or presence of C₂H₂. Soil respiration, nitrification rates and N₂O emissions by both processes were measured in relation to soil moisture conditions. At all WFPS studied, rates of N₂O and N₂ productions were small (4.8; 14.7; 23 and 239.6 ng N–N₂O g⁻¹ d.w. d⁻¹ at 39, 58, 76 and 87% WFPS, respectively), and despite a low soil pH (4.7), N₂O was mainly produced by nitrification, which was responsible for 85, 91, 84 and 87% of the total N₂O emissions at 39, 58, 76 and 87% WFPS, respectively. At the three smaller values of WFPS, a linear relationship was established between WFPS, soil respiration, nitrification and N₂O released by nitrification; no N₂ was produced by denitrification. At more anaerobic conditions achieved by a WFPS of 87%, a large rate of N₂O production was measured during nitrification, and N₂ production accounted for 84% of the gaseous N fluxes caused by denitrification.     

Nitrous oxide production in turfgrass systems: Effects of soil properties and grass clipping recycling

Soil N₂O emissions can affect global environments because N₂O is a potent greenhouse gas and ozone depletion substance. In the context of global warming, there is increasing concern over the emissions of N₂O from turfgrass systems. It is possible that management practices could be tailored to reduce emissions, but this would require a better understanding of factors controlling N₂O production. In the present study we evaluated the spatial variability of soil N₂O production and its correlation with soil physical, chemical and microbial properties. The impacts of grass clipping addition on soil N₂O production were also examined. Soil samples were collected from a chronosequence of three golf courses (10, 30, and 100-year-old) and incubated for 60 days at either 60% or 90% water filled-pore space (WFPS) with or without the addition of grass clippings or wheat straw. Both soil N₂O flux and soil inorganic N were measured periodically throughout the incubation. For unamended soils, cumulative soil N₂O production during the incubation ranged from 75 to 972 ng N g⁻¹ soil at 60% WFPS and from 76 to 8842 ng N g⁻¹ soil at 90% WFPS. Among all the soil physical, chemical and microbial properties examined, soil N₂O production showed the largest spatial variability with the coefficient of variation ~110% and 207% for 60% and 90% WFPS, respectively. At 60% WFPS, soil N₂O production was positively correlated with soil clay fraction (Pearson's r = 0.91, P < 0.01) and soil NH₄⁺–N (Pearson's r = 0.82, P < 0.01). At 90% WFPS, however, soil N₂O production appeared to be positively related to total soil C and N, but negatively related to soil pH. Addition of grass clippings and wheat straw did not consistently affect soil N₂O production across moisture treatments. Soil N₂O production at 60% WFPS was enhanced by the addition of grass clippings and unaffected by wheat straw (P < 0.05). In contrast, soil N₂O production at 90% WFPS was inhibited by the addition of wheat straw and little influenced by glass clippings (P < 0.05), except for soil samples with >2.5% organic C. Net N mineralization in soil samples with >2.5% organic C was similar between the two moisture regimes, suggesting that O₂ availability was greater than expected from 90% WFPS. Nonetheless, small and moderate changes in the percentage of clay fraction, soil organic matter content, and soil pH were found to be associated with large variations in soil N₂O production. Our study suggested that managing soil acidity via liming could substantially control soil N₂O production in turfgrass systems.     

Nitrous oxide emissions and controls as influenced by tillage and crop residue management strategy

Mixed responses of soil nitrous oxide (N₂O) fluxes to reduced tillage/no-till are widely reported across soil types and regions. In a field experiment on a Danish sandy loam soil we compared N₂O emissions during winter barley growth following five years of direct drilling (DD), reduced tillage (RT) or conventional tillage (CT). Each of these tillage treatments further varied in respect to whether the resulting plot crop residues were retained (+Res) or removed (−Res). Sampling took place from autumn 2007 to the end of spring 2008. Overall N₂O emissions were 27 and 26% lower in DD and RT, respectively, relative to N₂O emissions from CT plots (P < 0.05). We observed that in residue removal scenarios N₂O emissions were similar for all tillage treatments, but in residue retention scenarios N₂O emissions were significantly higher in CT than in either DD or RT (P < 0.05). Irrespective of residue management, N₂O emissions from DD and RT plots never exceeded emissions from CT plots. Retention of residue was estimated to reduce emissions from DD plots by 39% and in RT plots by 9%, but to increase N₂O emissions from the CT plots by 35%. Relative soil gas diffusivity (Rdiff), soil NO₃-N, soil temperature, tillage and residue were important driving factors for N₂O emission (P < 0.05). A multiple linear regression model using Rdiff to represent the water factor explained N₂O emissions better than a water-filled pore space (WFPS) based model, suggesting a need for review of the current use of WFPS in N₂O prediction models. We conclude that on light textured soils, no-till has the potential for reducing N₂O emissions when crop residues are returned to the soil.     

Effects of phosphorus addition on N2O and NO emissions from soils of an Acacia mangium plantation

Abstract

An incubation experiment was conducted to examine the effects of the phosphorus (P) application on nitrous oxide (N₂O) and nitric oxide (NO) emissions from soils of an Acacia mangium plantation in Indonesia. The soils were incubated with and without the addition of P (Ca[H₂PO₄]₂; 2 mg P g soil)^?1) after adjusting the water-filled pore space (WFPS) to 75% or 100%. The P addition increased N₂O emissions under both WFPS conditions and NO emissions at 75% WFPS. Some possible mechanisms are considered. First, the P addition stimulated nitrogen (N) cycling, and N used for nitrification and/or denitrification also increased. Second, the P addition could have relieved the P shortage for nitrifying and/or denitrifying bacteria, producing N₂O and NO. Our results suggest that the application of P fertilizer has the potential to stimulate N₂O and NO emissions from Acacia mangium plantations, at least when soils are under relatively wet conditions.     

Efficiency of nitrification inhibitor DMPP to reduce nitrous oxide emissions under different temperature and moisture conditions

Agricultural intensification has led to the use of very high inputs of nitrogen fertilizers into cultivated land. As a consequence of this, nitrous oxide (N₂O) emissions have increased significantly. Nowadays, the challenge is to mitigate these emissions in order to reduce global warming. Addition of nitrification inhibitors (NI) to fertilizers can reduce the losses of N₂O to the atmosphere, but field studies have shown that their efficiency varies depending greatly on the environmental conditions. Soil water content and temperature are key factors controlling N₂O emissions from soils and they seem to be also key parameters responsible for the variation in nitrification inhibitors efficiency. We present a laboratory study aimed at evaluating the effectiveness of the nitrification inhibitor 3,4-dimethylpyrazol phosphate (DMPP) at three different temperatures (10, 15 and 20 °C) and three soil water contents (40%, 60% and 80% of WFPS) on N₂O emissions following the application of 1.2 mg N kg⁻¹ dry soil (equivalent to 140 kg N ha⁻¹). Also the CO₂ and CH₄ emissions were followed to see the possible side effects of DMPP on the overall microbial activities. Nitrogen was applied either as ammonium sulfate nitrate (ASN) or as ENTEC 26 (ASN + DMPP). The application of ENTEC 26 was effective reducing N₂O losses up to the levels of an unfertilized control treatment in all conditions. Nevertheless, the percentage of reduction induced by DMPP in the ENTEC treatment with respect to the ASN varied from 3% to 45% depending on temperature and soil water content conditions. At 40% of WFPS, when nitrification is expected to be the main process producing N₂O, the increase of N₂O emissions in ASN together with temperature provoked an increase in DMPP efficiency reducing these emissions from 17% up to 42%. Contrarily, at 80% of WFPS, when denitrification is expected to be the main source of N₂O, emissions after ASN application decreased with temperature, which induced a decrease from 45% to 23% in the efficiency of DMPP reducing N₂O losses. Overall, the results obtained in this study suggest that DMPP performance regarding N₂O emissions reduction would be the best in cold and wet conditions. Neither CO₂ emissions nor CH₄ emissions were affected by the use of DMPP at the different soil water contents and temperatures.     

Assessing the benefits and wider costs of different N fertilisers for grassland agriculture

Fertiliser nitrogen (N) is essential for maintaining agronomic outputs for our growing population. However, the societal, economic and environmental impacts of excess reactive N from fertiliser is rarely assessed. Here the agronomic, economic and environmental efficacy of three N-fertiliser sources, ammonium-nitrate (AN), urea (U), and inhibited-urea (IU; with NPBT) were evaluated at two grassland sites. Dry matter yield and herbage quality were measured at each silage-cut. Additionally, NH₃-N and N₂O-N losses were measured and used to calculate the effective N source cost and externality costs, which account for associated environmental and societal impacts. We found no effect of different N sources on yield or herbage quality. However, NH₃-N emissions were significantly reduced under the IU treatment, by 48–65%. No significant differences in cumulative N₂O emissions were observed. Incorporating externality costs increased fertiliser prices by 1.23–2.36, 6.51–16.4, and 3.17–4.17 times the original cost, for AN, U and IU, respectively, transforming U from the cheapest, to the most expensive of the N sources examined. However, with no apparent yield differences between N-fertiliser sources there is no economic incentive for the land-manager to use the more environmentally and socially acceptable option, unless externality costs are incorporated into fertiliser prices at the point of sale.     

Soybean Residue Effect on Carbon Fractions and Gaseous Nitrogen Losses at Contrasting Moisture Contents

Most published studies related to crop effects on denitrification are not continuous and are based on the growing period. The objective of this work was to evaluate the effect of different amounts of soybean stubble, under different soil moisture contents, on gaseous nitrogen (N) losses by denitrification from an agricultural soil. The following soil moisture treatments were reached by adding distilled water to soil cores of a typic Hapludoll: 50 and 100% of water‐filled porosity space (WFPS). Residue treatments included no application of residues, amendment with 2600 kg ha^?1 of soybean residues, and amendment with 5200 kg ha^?1 of soybean residues. Cumulative nitrous oxide + dinitrogen (N₂O + N₂) emissions displayed great variability, ranging between 0 and 581.91 µg N kg^?1, which represented 0 to 3.93% of the N residue applied. Under 50% WFPS moisture conditions, statistical differences in cumulative N₂O + N₂ emissions between residue treatments were not detected (p = 0.21), whereas at saturation conditions, cumulative N₂O + N₂ emissions decreased with the application of increasing amounts of soybean residues (p = 0.017). Daily and cumulative N₂O + N₂ emissions significantly increased as soil moisture increased, except at soils amended with 5200 kg ha^?1 of soybean residues; this lack of statistical difference was probably due to the immobilization of native mineral N. Under 50% WFPS soil moisture contents, aeration seemed to be the main factor controlling redox conditions, limiting the denitrification process, and preventing differences in N emissions between residue treatments. The application of soybean residues to saturated soils notably decreased N₂O + N₂ emissions by denitrification through a strong mineral N immobilization into organic and nondenitrifiable forms.     

Nitrogen oxides emission from soils bearing a potato crop as influenced by fertilization with treated pig slurries and composts

Nitrous oxide, nitric oxide and denitrification losses from an irrigated soil amended with organic fertilizers with different soluble organic carbon fractions and ammonium contents were studied in a field study covering the growing season of potato (Solanum tuberosum). Untreated pig slurry (IPS) with and without the nitrification inhibitor dicyandiamide (DCD), digested thin fraction of pig slurry (DTP), composted solid fraction of pig slurry (CP) and composted municipal solid waste (MSW) mixed with urea were applied at a rate of 175 kg available N ha⁻¹, and emissions were compared with those from urea (U) and a control treatment without any added N fertilizer (Control). The cumulative denitrification losses correlated significantly with the soluble carbohydrates, dissolved N and total C added. Added dissolved organic C (DOC) and dissolved N affected the N₂O/N₂ ratio, and a lower ratio was observed for organic fertilizers than from urea or unfertilized controls. The proportion of N₂O produced from nitrification was higher from urea than from organic fertilizers. Accumulated N₂O losses during the crop season ranged from 3.69 to 7.31 kg N₂O-N ha⁻¹ for control and urea, respectively, whereas NO losses ranged from 0.005 to 0.24 kg NO-N ha⁻¹, respectively. Digested thin fraction of pig slurry compared to IPS mitigated the total N₂O emission by 48% and the denitrification rate by 33%, but did not influence NO emissions. Composted pig slurry compared to untreated pig slurry increased the N₂O emission by 40% and NO emission by 55%, but reduced the denitrification losses (34%). DCD partially inhibited nitrification rates and reduced N₂O and NO emissions from pig slurry by at least 83% and 77%, respectively. MSW+U, with a C:N ratio higher than that of the composted pig slurry, produced the largest denitrification losses (33.3 kg N ha⁻¹), although N₂O and NO emissions were lower than for the U and CP treatments.This work has shown that for an irrigated clay loam soil additions of treated organic fertilizers can mitigate the emissions of the atmospheric pollutants NO and N₂O in comparison with urea.     

The effect of moisture on nitrous oxide emissions from soil and the N<Subscript>2</Subscript>O/(N<Subscript>2</Subscript>O+N<Subscript>2</Subscript>) ratio under laboratory conditions

Nitrous oxide (N₂O) contributes to greenhouse effect; however, little information on the consequences of different moisture levels on N₂O/(N₂O+N₂) ratio is available. The aim of this work was to analyze the influence of different soil moisture values and thus of redox conditions on absolute and relative emissions of N₂O and N₂ at intact soil cores from a Vertic Argiudoll. For this reason, the effect of water-filled porosity space (WFPS) values of soil cores of 40, 80,100, and 120% (the last one with a 2-cm surface water layer) was investigated. The greatest N₂O emission occurred at 80% WFPS treatment where conditions were not reductive enough to allow the complete reduction to N₂. The N₂O/(N₂O+N₂) ratio was lowest (0–0.051) under 120% WFPS and increased with decreasing soil moisture content. N₂O/(N₂O+N₂) ratio values significantly correlated with soil Eh; redox conditions seemed to control the proportion of N gases emitted as N₂O. N₂O emissions did not correlate satisfactorily with N₂O/(N₂O+N₂) ratio values, whereas they were significantly explained by the amount of total N₂O+N₂ emissions.     

Laboratory study of the effects of two nitrification inhibitors on greenhouse gas emissions from a slurry-treated arable soil: impact of diurnal temperature cycle

An automated laboratory soil incubation system enabled the effects on gaseous emissions from a soil to be quantified accurately, when amended with slurry plus a nitrification inhibitor: dicyandiamide (DCD), or 3,4-dimethylpyrazole phosphate (DMPP). Nitrification inhibitors applied with slurry under simulated Portuguese conditions were very efficient in reducing N₂O emission, and did not increase CH₄ emissions significantly, when the soil was predominantly aerobic. The inhibitors were also indirectly effective in reducing N₂O emissions due to denitrification during a subsequent anaerobic phase. All gaseous emissions followed strong diurnal patterns that were positively correlated with soil temperature and obeyed a Q₁₀=2 relationship. The widespread use of DCD and DMPP inhibitors with slurry applied to Portuguese soils could have the potential to reduce N₂O emissions from this source by ten- to 20-fold.     

N<Subscript>2</Subscript>O emission from conventional and minimum-tilled soils

In this study, we investigated N₂O emissions from two fields under minimum tillage, cropped with maize (MT maize) and summer oats (MT oats), and a conventionally tilled field cropped with maize (CT maize). Nitrous oxide losses from the MT maize and MT oats fields (5.27 and 3.64 kg N₂O-N ha⁻¹, respectively) were significantly higher than those from the CT maize field (0.27 kg N₂O-N ha⁻¹) over a period of 1 year. The lower moisture content in CT maize (43% water-filled pore space [WFPS] compared to 60–65%) probably caused the difference in total N₂O emissions. Denitrification was found to be the major source of N₂O loss. Emission factors calculated from the MT field data were high (0.04) compared to the CT field (0.001). All data were simulated with the denitrification decomposition model (DNDC). For the CT field, N₂O and N₂O + N₂ emissions were largely overestimated. For the MT fields, there was a better agreement with the total N₂O and N₂O + N₂ emissions, although the N₂O emissions from the MT maize field were underestimated. The simulated N₂O emissions were particularly influenced by fertilization, but several other measured N₂O emission peaks associated with other management practices at higher WFPS were not captured by the model. Several mismatches between simulated and measured \textNH₄⁺ {\text{NH}}_4^ + , \textNO₃^- {\text{NO}}_3^ - and WFPS for all fields were observed. These mismatches together with the insensitivity of the DNDC model for increased N₂O emissions at the management practices different from fertilizer application explain the limited similarity between the simulated and measured N₂O emissions pattern from the MT fields.