Nitrous oxide emission from an irrigated cotton field under semiarid subtropical conditions

In a 1-year study, quantification of nitrous oxide (N₂O) emission was made from a flood-irrigated cotton field fertilized with urea at 100kg N ha⁻¹ a⁻¹. Measurements were made during the cotton-growing season (May–November) and the fallow period (December–April). Of the total 95 sampling dates, 77 showed positive N₂O fluxes (range, 0.1 to 33.3g N ha⁻¹ d⁻¹), whereas negative fluxes (i.e., N₂O sink activity) were recorded on 18 occasions (range, −0.1 to −2.2g N ha⁻¹ d⁻¹). Nitrous oxide sink activity was more frequently observed during the growing season (15 out of 57 sampling dates) as compared to the fallow period (3 out of 38 sampling dates). During the growing season, contribution of N₂O to the denitrification gaseous N products was much less (average, 4%) as compared to that during the fallow period (average, 21%). Nitrous oxide emission integrated over the 6-month growing period amounted 324g N ha⁻¹, whereas the corresponding figure for the 6-month fallow period was 648g N ha⁻¹. Subtracting the N₂O sink activity (30.3g N ha⁻¹ and 3.8g N ha⁻¹ during the growing season and fallow period, respectively), the net N₂O emission amounted 938g N ha⁻¹ a⁻¹. Results suggested that high soil moisture and temperature prevailing under flood-irrigated cotton in the Central Punjab region of Pakistan though favor high denitrification rates, but are also conducive to N₂O reduction thus leading to relatively low N₂O emission.     

Nitrous oxide emission from urine-treated soil as influenced by urine composition and soil physical conditions

Urine patches from cattle and sheep on pastures represent considerable, highly localized N applications. Subsequent nitrification and denitrification of the nitrogenous compounds may result in high nitrous oxide (N₂O) emissions. Not much is known about the extent of these emissions, or about possible mitigation options. The aims of this study were to experimentally quantify the effects of urine composition, dung addition, compaction and soil moisture on N₂O emissions from urine patches. For an incubation study at 16 °C, soil was collected from a typic Endoaquoll, and N₂O production was monitored during a 103-day period. Emissions for the whole period averaged 0.3 and 0.9% of the applied urine-N for dry and moist soil, respectively. When compacted or when dung was added, emissions from moist soils increased to 4.9 and 7.9%, respectively. Both addition of dung and soil compaction resulted in a delay of the peak N₂O emission of approximately 10-15 days. No significant effect of amount of urine-N on emission percentages was detected. Changing the volume of urine with equal amounts of urine-N resulted in highly significant effects, peaking with an emission of 2.3% at a water-filled pore space (WFPS) of 78%. When the soil was water-saturated, N₂O production was delayed until evaporation had decreased moisture contents. We concluded that denitrification was the main N₂O forming process in the incubation study. Emission factors for urine reported in the literature do not generally include the potentially considerable effects of compaction or combination with dung. We conclude that realistic emission factors should take into account such an effect, together with estimates for the occurrence of camping areas in pastures. From our results, the best mitigation strategies appear to be increasing the volume of urine through feed additives, and avoiding compaction and promoting more homogeneous application of N through a lower cattle stocking rate. Also, research efforts may be targeted at management practices to avoid camping areas in pastures.     

Nitrous oxide emissions under different soil and land management conditions

Nitrous oxide (N₂O) emissions of three different soils – a rendzina on cryoturbed soil, a hydromorphic leached brown soil and a superficial soil on a calcareous plateau – were measured using the chamber method. Each site included four types of land management: bare soil, seeded unfertilized soil, a suboptimally fertilized rapeseed crop and an overfertilized rapeseed crop. Fluxes varied from –1g to 100g N₂O-nitrogen ha^–1 day^–1. The highest rates of N₂O emissions were measured during spring on the hydromorphic leached brown soil which had been fertilized with nitrogen (N); the total emissions during a 5-month period exceeded 3500gNha^–1. Significant fluxes were also observed during the summer. Very marked effects of soil type and management were observed. Two factors – the soil hydraulic behaviour and the ability of the microbial population to reduce N₂O – appear to be essential in determining emissions of N₂O by soils. In fact, the hydromorphic leached brown soil showed the highest emissions, despite having the lowest denitrification potential because of its water-filled pore space and low N₂O reductase activity. Soil management also appears to affect both soil nitrate content and N₂O emissions. Received: 4 April 1997     

Nitrous oxide emission from feedlot manure and green waste compost applied to Vertisols

Application of feedlot manure (FLM) to cropping and grazing soils could provide a valuable N nutrient resource. However, because of its high but variable N concentration, FLM has the potential for environmental pollution of water bodies and N₂O emission to the atmosphere. As a potential management tool, we utilised the low-nutrient green waste compost (GWC) to assess its effectiveness in regulating N release and the amount of N₂O emission from two Vertisols when both FLM and GWC were applied together. Cumulative soil N₂O emission over 32 weeks at 24°C and field capacity (70% water-filled pore space) for a black Vertisol (Udic Paleustert) was 45 mg N₂O m⁻² from unamended soil. This increased to 274 mg N₂O m⁻² when FLM was applied at 1 kg m⁻² and to 403 mg N₂O m⁻² at 2 kg m⁻². In contrast, the emissions of 60 mg N₂O m⁻² when the soil was amended with GWC 1 kg m⁻² and 48 mg N₂O m⁻² at 2 kg m⁻² were not significantly greater than the unamended soil. Emission from a mixture of FLM and GWC applied in equal amounts (0.5 kg m⁻²) was 106 mg N₂O m⁻² and FLM applied at 0.5 kg m⁻² and GWC at 1.5 kg GWC m⁻² was 117 mg N₂O m⁻². Although cumulative N₂O emissions from an unamended grey Vertisol (Typic Chromustert) were only slightly higher than black Vertisol (57 mg N₂O m⁻²), FLM application at 1 kg m⁻² increased N₂O emissions by 14 times (792 mg N₂O m⁻²) and at 2 kg m⁻² application by 22 times (1260 mg N₂O m^-2). Application of GWC did not significantly increase N₂O emission (99 mg N₂O m⁻² at 1 kg m⁻² and 65 mg N₂O m⁻² at 2 kg m⁻²) above the unamended soil. As observed for the black Vertisol, a mixture of FLM (0.5 kg m⁻²) and GWC (0.5 or 1.5 kg m⁻²) reduced N₂O emission by >50% of that from the FLM alone, most likely by reducing the amount of mineral N (NH₄⁺–N and NO₃⁻–N) in the soil, as mineral N in soil and the N₂O emission were closely correlated.     

Nitrous oxide emission from frozen grassland soil and during thawing periods

Nitrous oxide (N₂O) was emitted during a frost period from an old grassland as well as during thawing. Soil incubations at various times throughout the freezing period showed that highest emission rates were emitted around 0 °C, and the magnitude of the emission peak increased with the length of the freezing period. Highest N₂O emissions during freezing and thawing were measured from soil previously treated with nitrate (NO₃^‐). The emitted N₂O was produced via reduction of NO₃^‐. The steady drop in N₂O emission at soil temperatures higher than 2 °C coincided with large dinitrogen (N₂) emissions which most likely reflected the increasing enzymatic activity of N₂O reductase with increasing temperatures. Measurements of mineral N concentrations showed that NO₃^‐ and NH₄⁺, which were shortly after fertilizer application immobilized into the microbial biomass, became partly available again through the freezing effect and caused large N₂O emissions in winter. This study provided evidence that N₂O emissions during freezing and thawing in the winter are due to biological rather than chemical activity in soil.     

Nitrous oxide emission from herbicide-treated soybean

 The emission of N₂O from soybean plants treated with the herbicides dichlorophenoxyacetic acid (2,4-D) and bromoxynil was studied. The N₂O flux from 2,4-D- and bromoxynil-treated soybean was 14.1 ng N₂O-N g^–1 fresh weight h^–1 and 19.7 ng N₂O-N g^–1 fresh weight h^–1, respectively, i.e. approximately twice that of the controls. The NO₂ ^–-N concentration in 2,4-D- and in bromoxynil-treated soybean was about 8 μg N g^–1 fresh weight, i.e. fivefold the concentration found in control plants. The NO₃ ^– content in herbicide-treated soybean did not differ significantly from that of the control plants. Consequently, the accumulation of NO₂ ^–-N during the assimilation of NO₃ ^–-N was thought to cause the observed N₂O release. Probably, N₂O is a by-product produced during either the reaction of NO₂ ^–-N with plant metabolites or NO₂ ^–-N decomposition. Final conclusions must await further experiments. Received: 5 November 1999     

Nitrous oxide emissions from dairy farm effluent applied to a New Zealand pasture soil

A field experiment on permanent ryegrass–white clover pasture at AgResearch's Ruakura dairy farm near Hamilton, New Zealand quantified nitrous oxide (N₂O) emissions from different types of dairy effluent applied to soil at three seasons and evaluated the potential of dicyandiamide (DCD) (a nitrification inhibitor) to decrease gaseous N₂O emissions. Fresh or stored manure and farm dairy effluent (FDE; from dairy shed washings), with or without DCD (10 kg/ha), were applied at approximately 100 kg N/ha to plots on a well‐drained soil on volcanic parent material. A field chamber technique was used to measure N₂O emissions. Application of manure or FDE, both in fresh and stored forms, to pasture generally increased N₂O emissions. Overall N₂O emission factors (EF) varied between 0.01% and 1.87%, depending on application season and effluent type. EFs in spring and autumn were greater than those in summer (P < 0.05). Among the effluents, N₂O EFs were largest from fresh FDE (1.65%) during the spring measurement period, stored manure (1.87%) during the autumn and stored FDE (0.25%) during the summer. DCD was effective in decreasing N₂O EFs from fresh FDE, fresh manure, stored FDE and stored manure by 40–80%, 69–76%, 24–84% and 60–70%, respectively. DCD reduced N₂O emissions during the spring and autumn seasons more effectively than in the summer season.     

Nitrous oxide emissions from boreal organic soil under different land-use

Nitrous oxide emissions were studied with a static chamber technique during 2 years from a drained organic soil in eastern Finland. After drainage, the soil was forested with birch (Betula pendula Roth) and 22 years later, part of the forest was felled and then used for cultivation of barley (Hordeum vulgare L.) and grass. The annual N₂O emissions from the cultivated soil (from 8.3 to 11.0 kg N₂O-N ha⁻¹ year⁻¹) were ca. twice the annual emission from the adjacent forest site (4.2 kg N₂O-N ha⁻¹ year⁻¹). The N₂O emissions from the soils without plants (kept bare by regular cutting or tilling) were also lower (from 6.5 to 7.1 kg N₂O-N ha⁻¹ year⁻¹) than those from the cultivated soil. There was a high seasonal variation in the fluxes with a maximum in spring and early summer. The N₂O fluxes during the winter period accounted for 15-60% of the total annual emissions. N₂O fluxes during the snow-free periods were related to the water table (WT) level, water-filled pore space, carbon mineralisation and the soil temperature. A linear regression model with CO₂ production, WT and soil temperature at the depth of 5 cm as independent variables explained 54% of the variation in the weekly mean N₂O fluxes during the snow-free periods. N₂O fluxes were associated with in situ net nitrification, which alone explained 58% of the variation in the mean N₂O fluxes during the snow-free period. The N₂O-N emissions were from 1.5 to 5% of net nitrification. The acetylene blockage technique indicated that most of the N₂O emitted in the snow-free period originated from denitrification.     

Nitrous oxide emission as affected by alternate anaerobic and aerobic conditions from soil suspensions enriched with ammonium sulfate

The effect of several anaerobic and aerobic cycles of varying duration on N₂O emission and labelled N loss was investigated in (¹⁵NH₄)₂SO₄ amended soil suspensions. No N₂O was evolved from the continuously-anaerobic treatment. The continuously-aerobic treatment produced approximately 0.8 μg N₂O-N g^?1 dry soil in 56 days. Alternate anaerobic-aerobic cycles increased the net N₂O evolution with 7.2 μg N₂O-N g^?1 dry soil produced in 56 days from the 7-day anaerobic, 7-day aerobic treatment. The net N₂O evolution increased further when the duration of the anaerobic and aerobic periods was increased from 7-7 days to 14-14 days (15.7μg N₂O-N g^?1 dry soil in 56 days), although the total ¹⁵N loss from the system was approximately the same for the two treatments. The results of this study show that N₂O evolution from soils is likely to be greater under fluctuating moisture conditions than under either continuously well-aerated conditions, or continuously excess-moisture conditions.     

Nitrous oxide emission from a grassland soil fertilized with slurry and calcium nitrate

Concentrations of nitrous oxide (N₂O) and oxygen were monitored over a 2-yr period in an imperfectly drained grassland soil receiving applications of N as cattle slurry or Ca(NO₃)₂. In both years N₂O concentrations in the different treatments were in the order nitrate > slurry > control. Gaseous diffusion coefficients were determined in soil cores by a krypton-85 tracer method and used to calculate approximate N₂O fluxes from the soil. Only 1–5 kg N ha^?1 was lost as N₂O after a single application of > 1200 kg N ha ^?1 as slurry compared with 3–11 kg N ha ^?1 lost after 100 kg was added as NO₃^?. Total gaseous losses (N₂O+N₂) could be expected to be higher in both cases.     

Nitrous oxide emission from the soil surface: Continuous measurement by gas chromatography

Nitrous oxide flux from the soil is determined by drawing atmospheric air through chambers on the soil surface and measuring the N₂O-content, using a gas Chromatograph (GC). The N₂O-concentration can be at least 2 times higher within the box than outside without altering the measured N₂O-flux. The flow through the chamber is not sufficient to produce pressure effects on the N₂O-concentration in the box. The effects of the chamber on soil temperature are negligible.     

Nitrous oxide emission derived from soil organic matter decomposition from tropical agricultural peat soil in central Kalimantan,Indonesia

Our previous research showed large amounts of nitrous oxide (N₂O) emission (>200?kg?N?ha^?1?year^?1) from agricultural peat soil. In this study, we investigated the factors influencing relatively large N₂O fluxes and the source of nitrogen (N) substrate for N₂O in a tropical peatland in central Kalimantan, Indonesia. Using a static chamber method, N₂O and carbon dioxide (CO₂) fluxes were measured in three conventionally cultivated croplands (conventional), an unplanted and unfertilized bare treatment (bare) in each cropland, and unfertilized grassland over a three-year period. Based on the difference in N₂O emission from two treatments, contribution of the N source for N₂O was calculated. Nitrous oxide concentrations at five depths (5–80?cm) were also measured for calculating net N₂O production in soil. Annual N fertilizer application rates in the croplands ranged from 472 to 1607?kg?N?ha^?1?year^?1. There were no significant differences in between N₂O fluxes in the two treatments at each site. Annual N₂O emission in conventional and bare treatments varied from 10.9 to 698 and 6.55 to 858?kg?N?ha^?1?year^?1, respectively. However, there was also no significant difference between annual N₂O emissions in the two treatments at each site. This suggests most of the emitted N₂O was derived from the decomposition of peat. There were significant positive correlations between N₂O and CO₂ fluxes in bare treatment in two croplands where N₂O flux was higher than at another cropland. Nitrous oxide concentration distribution in soil measured in the conventional treatment showed that N₂O was mainly produced in the surface soil down to 15?cm in the soil. The logarithmic value of the ratio of N₂O flux and nitrate concentration was positively correlated with water filled pore space (WEPS). These results suggest that large N₂O emission in agricultural tropical peatland was caused by denitrification with high decomposition of peat. In addition, N₂O was mainly produced by denitrification at high range of WFPS in surface soil.     

Nitrous oxide emission from soils after incorporating crop residues

Abstract. Emissions of N₂O were measured from different agricultural systems in SE Scotland. N₂O emissions increased temporarily after fertilization of arable crops, cultivation of bare soil, ploughing up of grassland and incorporation of arable and horticultural crop residues, but the effect was short-lived. Most of the emission occurred during the first two weeks, returning to 'background' levels after 30–40 days. The highest flux was from N-rich lettuce residues, 1100 g N₂O-N ha⁻¹ being emitted over the first 14 days after incorporation by rotary tillage. The magnitude and pattern of emissions was strongly influenced by rainfall, soil mineral N, cultivation technique and C:N ratio of the residue. Comparatively large emissions were measured after incorporation of material with low C:N ratios. Management practices are recommended that would increase N-use efficiency and reduce N₂O emissions from agricultural soils.     

Nitrous oxide emission from soils at low moisture contents

The production of nitrous oxide by soils was studied over short periods at a range of moisture contents up to field capacity with a highly-sensitive gas Chromatographic method.Nitrous oxide (N₂O) was emitted from all soils studied at all soil moisture contents, which ranged from air dry to field capacity. The rate of emission increased with increasing moisture content and with increasing temperature up to 37°C.The evolution of N₂O was not due to displacement of soil air during wetting. It was inhibited by HgCl₂ and toluene, and was prevented by formaldehyde and autoclaving. Thus it appeared to be due to microbiological processes.The results of experiments with nitrification and denitrification inhibitors suggest that a considerable part of the N₂O was produced by the oxidation of ammonia. Production by denitrification of nitrate cannot be ruled out. The relative importance of these two mechanisms probably depends on the moisture and oxygen content of the soil.It is concluded that the microbial production of N₂O is continuous in soil at all moisture contents. The process at low moisture contents constitutes an important component in the cycle which maintains the N₂O concentration in the atmosphere.     

Nitrous oxide flux from soil amino acid mineralization

Nitrous oxide (N₂O) is a greenhouse gas produced during microbial transformation of soil N that has been implicated in global climate warming. Nitrous oxide efflux from N fertilized soils has been modeled using NO₃⁻ content with a limited success, but predicting N₂O production in non-fertilized soils has proven to be much more complex. The present study investigates the contribution of soil amino acid (AA) mineralization to N₂O flux from semi-arid soils. In laboratory incubations (−34 kPa moisture potential), soil mineralization of eleven AAs (100 μg AA-N g⁻¹ soil) promoted a wide range in the production of N₂O (156.0±79.3 ng N₂O-N g⁻¹ soil) during 12 d incubations. Comparison of the δ¹³C content (‰) of the individual AAs and the δ¹³C signature of the respired AA-CO₂-C determined that, with the exception of TYR, all of the AAs were completely mineralized during incubations, allowing for the calculation of a N₂O-N conversion rate from each AA. Next, soils from three different semi-arid vegetation ecosystems with a wide range in total N content were incubated and monitored for CO₂ and N₂O efflux. A model utilizing CO₂ respired from the three soils as a measure of organic matter C mineralization, a preincubation soil AA composition of each soil, and the N₂O-N conversion rate from the AA incubations effectively predicted the range of N₂O production by all three soils. Nitrous oxide flux did not correspond to factors shown to influence anaerobic denitrification, including soil NO₃⁻ contents, soil moisture, oxygen consumption, and CO₂ respiration, suggesting that nitrification and aerobic nitrifier denitrification could be contributing to N₂O production in these soils. Results indicate that quantification of AA mineralization may be useful for predicting N₂O production in soils.     

Nitrous oxide emission from a soil under permanent grass: Seasonal and diurnal fluctuations as influenced by manuring and fertilization

The emission of nitrous oxide (N₂O) from soil under grass was measured, following applications of cow slurry and NH₄NO₃ fertilizer. The N₂O-flux from untreated soil averaged 0.58 mg Nm^?2 day^?1 through April to August. Application of slurry at the end of April and at the middle of July caused increases in the daily N₂O-flux of up to 40-fold, compared to untreated grass. Applications of NH₄NO₃ increased the N₂O-flux up to 5 times during the same period. The N₂O-flux often showed marked diurnal fluctuations. These fluctuations are not solely associated with change in temperature, but may also be related to grass root activity and to photosynthesis.     

Soil and residue management effects on cropping conditions and nitrous oxide fluxes under controlled traffic in Scotland2. Nitrous oxide, soil N status and weather

Nitrogen from fertilisers and crop residues can be lost as nitrous oxide (N₂O), a greenhouse gas that causes an increase in global warming and also depletes stratospheric ozone. Nitrous oxide emissions, soil chemical status, temperature and N₂O concentration in the soil atmosphere were measured in a field experiment on soil compaction in loam and sandy loam (cambisols) soils in south-east Scotland. The overall objective was to discover how the intensity and distribution of soil compaction by tractor wheels or by roller just before sowing influenced crop performance, soil conditions and production and emissions of N₂O under controlled traffic conditions. Compaction treatments were zero, light compaction by roller (up to 1 Mg per metre of length) and heavy compaction by loaded tractor (up to 4.2 Mg). In this paper we report the effects on production and emissions of N₂O and relate them to soil and crop conditions. Nitrous oxide fluxes were substantial only when the soil water content was high (>27 g per 100 g). Fertiliser application stimulated emissions in the spring whereas crop residues stimulated emissions in autumn and winter. Heavy compaction increased N₂O emissions after fertiliser application or residue incorporation more than light or zero compaction. The bulk densities of the heavily and lightly compacted soils were up to 89% and 82% of the theoretical (Proctor) maxima. Higher soil cone resistances, temperatures and nitrogen availability and lower gas diffusivities and air-filled porosities combined to make the heavily compacted soil more anaerobic and likely to denitrify than the zero or lightly compacted soil. Compaction sufficient to increase N₂O emissions significantly corresponded with adverse soil conditions for winter barley (Hordeum vulgare L.) growth. Soil tillage, which ensures that soil compaction is no greater than in our light treatment and is confined to near the soil surface, may help to mitigate both surface fluxes of N₂O and losses to the subsoil.     

Nitrous oxide emission from simulated overland flow wastewater treatment systems

Nitrous oxide evolution was measured from overland flow models receiving daily applications of municipal wastewater with NH₄⁺-N concentration in the wastewater of 10 or 47 μgN ml^?1. The amount of N₂O evolved from the system ranged from 0.07 to 1.3 mg N day^?1, or 1.5–25.5 kg N ha^?1yr^?1, respectively. Liming the soil or increasing the NH₄⁺-N in the wastewater increased the emission of N₂O from the system. The N evolved as N₂O did not exceed 1.2% of the applied NH₄⁺-N, indicating N₂ to be the major denitrification end product in the overland flow wastewater-treatment system.     

Nitrogen mineralization of silk waste applied to soil under aerobic conditions

Silk waste which is a byproduct of silk reeling consists mainly of silk proteins such as sericin and fibroin. Although silk waste has a high N content (164 g kg^-1) and low CjN ratio (2.16), net N mineralization in soil at 30°C under aerobic conditions was very slow (21.4% in 184 d). The N mineralization rate of silk waste applied to soil after hydrolysis with HCI was higher than that of untreated silk waste. The effect of hydrolysis with 0.2 M HCI for 60 min at 97°C on the net N mineralization for 56 d was twice as high as that with 1 M HCI for 60 min at 97°C. Molecular mass distribution of silk proteins shifted to the lower range by hydrolysis, whose effect with 1 M HCI was more pronounced than that with 0.2 M HCI. The content of the crystal region in silk protein was estimated to be approximately 45% based on the relationship between the reaction (acid hydrolysis) time and the weight of insoluble residues. X-ray diffraction patterns of these residues showed that the crystal structure persisted until at least 180 min after hydrolysis with 1 M HCI at 97°C. These results suggest that crystal regions and the scattered distribution in silk proteins inhibit the decomposition of silk waste in soil. Silk waste could thus be utilized as slow-release fertilizer.