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.     

The effect of reduced tillage on nitrous oxide emissions of silt loam soils

The effect of reduced tillage (RT) on nitrous oxide (N₂O) emissions of soils from fields with root crops under a temperate climate was studied. Three silt loam fields under RT agriculture were compared with their respective conventional tillage (CT) field with comparable crop rotation and manure application. Undisturbed soil samples taken in September 2005 and February 2006 were incubated under laboratory conditions for 10 days. The N₂O emission of soils taken in September 2005 varied from 50 to 1,095 μg N kg⁻¹ dry soil. The N₂O emissions of soils from the RT fields taken in September 2005 were statistically (P < 0.05) higher or comparable than the N₂O emissions from their respective CT soil. The N₂O emission of soils taken in February 2006 varied from 0 to 233 μg N kg⁻¹ dry soil. The N₂O emissions of soils from the RT fields taken in February 2006 tended to be higher than the N₂O emissions from their respective CT soil. A positive and significant Pearson correlation of the N₂O–N emissions with nitrate nitrogen (NO₃ ⁻–N) content in the soil was found (P < 0.01). Leaving the straw on the field, a typical feature of RT, decreased NO₃ ⁻–N content of the soil and reduced N₂O emissions from RT soils.     

Spatial variability and biophysicochemical controls on N<Subscript>2</Subscript>O emissions from differently tilled arable soils

Nitrous oxide (N₂O) emissions, soil microbial community structure, bulk density, total pore volume, total C and N, aggregate mean weight diameter and stability index were determined in arable soils under three different types of tillage: reduced tillage (RT), no tillage (NT) and conventional tillage (CT). Thirty intact soil cores, each in a 25 × 25-m² grid, were collected to a depth of 10 cm at the seedling stage of winter wheat in February 2008 from Maulde (50°3′ N, 3°43′ W), Belgium. Two additional soil samples adjacent to each soil core were taken to measure the spatial variance in biotic and physicochemical conditions. The microbial community structure was evaluated by means of phospholipid fatty acids analysis. Soil cores were amended with 15 kg NO₃⁻-N ha⁻¹, 15 kg NH₄⁺-N ha⁻¹ and 30 kg ha⁻¹ urea-N ha⁻¹ and then brought to 65% water-filled pore space and incubated for 21 days at 15°C, with regular monitoring of N₂O emissions. The N₂O fluxes showed a log-normal distribution with mean coefficients of variance (CV) of 122%, 78% and 90% in RT, NT and CT, respectively, indicating a high spatial variation. However, this variability of N₂O emissions did not show plot scale spatial dependence. The N₂O emissions from RT were higher (p < 0.01) than from CT and NT. Multivariate analysis of soil properties showed that PC1 of principal component analysis had highest loadings for aggregate mean weight diameter, total C and fungi/bacteria ratio. Stepwise multiple regression based on soil properties explained 72% (p < 0.01) of the variance of N₂O emissions. Spatial distributions of soil properties controlling N₂O emissions were different in three different tillages with CV ranked as RT > CT > NT.     

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.     

Nitrous oxide emissions from an irrigated sandy-clay loam cropped to maize and wheat

 Nitrous oxide (N₂O) emissions were measured from an irrigated sandy-clay loam cropped to maize and wheat, each receiving urea at 100 kg N ha^–1. During the maize season (24 August–26 October), N₂O emissions ranged between –0.94 and 1.53 g N ha^–1 h^–1 with peaks during different irrigation cycles (four) ranging between 0.08 and 1.53 g N ha^–1 h^–1. N₂O sink activity during the maize season was recorded on 10 of the 29 sampling occasions and ranged between 0.18 and 0.94 g N ha^–1 h^–1. N₂O emissions during the wheat season (22 November–20 April) varied between –0.85 and 3.27 g N ha^–1 h^–1, whereas peaks during different irrigation cycles (six) were in the range of 0.05–3.27 g N ha^–1 h^–1. N₂O sink activity was recorded on 14 of the 41 samplings during the wheat season and ranged between 0.01 and 0.87 g N ha^–1 h^–1. Total N₂O emissions were 0.16 and 0.49 kg N ha^–1, whereas the total N₂O sink activity was 0.04 and 0.06 kg N ha^–1 during the maize and wheat seasons, respectively. N₂O emissions under maize were significantly correlated with denitrification rate and soil NO₃ ^–-N but not with soil NH₄ ⁺-N or soil temperature. Under wheat, however, N₂O emissions showed a strong correlation with soil NH₄ ⁺-N, soil NO₃ ^–-N and soil temperature but not with the denitrification rate. Under either crop, N₂O emissions did not show a significant relationship with water-filled pore space or soil respiration. Received: 11 June 1997     

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.     

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 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.     

Nitrogen mineralization and CO2 and N2O emissions in a sandy soil amended with original or acidified pig slurries or with the relative fractions

The following six pig slurries obtained after acidification and/or solid/liquid separation were used in the research: original (S) and acidified (AS) pig slurry, nonacidified (LF) and acidified (ALF) pig slurry liquid fraction, and nonacidified (SF) and acidified (ASF) pig slurry solid fraction. Laboratory incubations were performed to assess the effect of the application of these slurries on N mineralization and CO₂ and N₂O emissions from a sandy soil. Acidification maintained higher NH₄ ⁺-N contents in soil particularly in the ALF-treated soil where NH₄ ⁺-N contents were two times higher than in LF-treated soil during the 55–171-day interval. At the end of the incubation (171 days), 32.9 and 24.2 mg N kg⁻¹ dry soil were mineralized in the ASF- and SF-treated soils, respectively, but no mineralization occurred in LF- and S-treated soils, although acidification decreased N immobilization in ALF- (−25.3 mg N kg⁻¹ soil) and AS- (−12.7 mg N kg⁻¹ soil) compared to LF- (−34.4 mg N kg⁻¹ soil) and S-treated (−18.6 mg N kg⁻¹ soil) soils, respectively. Most of the dissolved CO₂ was lost during the acidification process. More than 90% of the applied C in the LF-treated soil was lost during the incubation, indicating a high availability of the added organic compounds. Nitrous oxide emissions occurred only after day 12 and at a lower rate in soils treated with acidified than nonacidified slurries. However, during the first 61 days of incubation, 1,157 μg N kg⁻¹ soil was lost as N₂O in the AS-treated soil and only 937 in the S-treated soil.     

Seasonal variations of nitrous oxide emission in relation to nitrogen fertilization and energy crop types in sandy soil

Nitrous oxide (N₂O) is a greenhouse gas and agricultural soils are major sources of atmospheric N₂O. Its emissions from soils make up the largest part in the global N₂O budget. Research was carried out at the experimental fields of the Leibniz-Institute of Agricultural Engineering Potsdam-Bornim (ATB). Different types (mineral and wood ash) and levels (0, 75 and 150 kg N ha⁻¹) of fertilization were applied to annual (rape, rye, triticale and hemp) and perennial (poplar and willow) plants every year. N₂O flux measurements were performed 4 times a week by means of gas flux chambers and an automated gas chromatograph between 2003 and 2005. Soil samples were also taken close to the corresponding measuring rings. Soil nitrate and ammonium were measured in soil extracts.N₂O emissions had a peak after N fertilization in spring, after plant harvest in summer and during the freezing–thawing periods in winter. Both fertilization and plant types significantly altered N₂O emission. The maximum N₂O emission rate detected was 1081 μg N₂O m⁻² h⁻¹ in 2004. The mean annual N₂O emissions from the annual plants were more than twofold greater than those of perennial plants (4.3 kg ha⁻¹ vs. 1.9 kg ha⁻¹). During January, N₂O fluxes considerably increased in all treatments due to freezing–thawing cycles. Fertilization together with annual cropping doubled the N₂O emissions compared to perennial crops indicating that N use efficiency was greater for perennial plants. Fertilizer-derived N₂O fluxes constituted about 32% (willow) to 67% (rape/rye) of total soil N₂O flux. Concurrent measurements of soil water content, NO₃ and NH₄ support the conclusion that nitrification is main source of N₂O loss from the study soils. The mean soil NO₃-N values of soils during the study for fertilized soils were 1.6 and 0.9 mg NO₃-N kg⁻¹ for 150 and 75 kg N ha⁻¹ fertilization, respectively. This value reduced to 0.5 mg NO₃-N kg⁻¹ for non-fertilized soils.     

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.     

Effect of soil water status and mulching on N<Subscript>2</Subscript>O and CH<Subscript>4</Subscript> emission from lowland rice field in China

Cultivation of rice in unsaturated soils covered with mulch is receiving more attention in China because of increasingly serious water shortage; however, greenhouse gas emission from this cultivation system is still poorly understood. A field experiment was conducted in 2001 to compare nitrous oxide (N₂O) and methane (CH₄) emission from rice cultivated in unsaturated soil covered with plastic or straw mulch and the traditional waterlogged production system. Trace gas fluxes from the soil were measured weekly throughout the entire growth period using a closed chamber method. Nitrous oxide emissions from unsaturated rice fields were large and varied considerably during the rice season. They were significantly affected by N fertilizer application rate. In contrast, N₂O emission from the waterlogged system was very low with a maximum of 0.28 mg N₂O m^–2 h^–1. However, CH₄ emission from the waterlogged system was significantly higher than from the unsaturated system, with a maximum emission rate of 5.01 mg CH₄ m^–2 h^–1. Our results suggested that unsaturated rice cultivation with straw mulch reduce greenhouse gas emissions.     

Tillage effects on N2O emissions as influenced by a winter cover crop

Conservation tillage practices are widely used to protect against soil erosion and soil C losses, whereas winter cover crops are used mainly to protect against N losses during autumn and winter. For the greenhouse gas balance of a cropping system the effect of reduced tillage and cover crops on N₂O emissions may be more important than the effect on soil C. This study monitored emissions of N₂O between September 2008 and May 2009 in three tillage treatments, i.e., conventional tillage (CT), reduced tillage (RT) and direct drilling (DD), all with (+CC) or without (−CC) fodder radish as a winter cover crop. Cover crop growth, soil mineral N dynamics, and other soil characteristics were recorded. Furthermore, soil concentrations of N₂O were determined eight times during the monitoring period using permanently installed needles. There was little evidence for effects of the cover crop on soil mineral N. Following spring tillage and slurry application soil mineral N was dominated by the input from slurry. Nitrous oxide emissions during autumn, winter and early spring remained low, although higher emissions from +CC treatments were indicated after freezing events. Following spring tillage and slurry application by direct injection N₂O emissions were stimulated in all tillage treatments, reaching 250-400 μg N m⁻² h⁻¹ except in the CT + CC treatment, where emissions peaked at 900 μg N m⁻² h⁻¹. Accumulated emissions ranged from 1.6 to 3.9 kg N₂O ha⁻¹. A strong positive interaction between cover crop and tillage was observed. Soil concentration profiles of N₂O showed a significant accumulation of N₂O in CT relative to RT and DD treatments after spring tillage and slurry application, and a positive interaction between slurry and cover crop residues. A comparison in early May of N₂O emissions with flux estimates based on soil concentration profiles indicated that much of the N₂O emitted was produced near the soil surface.     

Compaction influences N2O and N2 emissions from 15N-labeled synthetic urine in wet soils during successive saturation/drainage cycles

Nitrous oxide emitted from urine patches is a key source of agricultural greenhouse gas emissions. A better understanding of the complex soil environmental and biochemical regulation of urine-N transformations in wet soils is needed to predict N₂O emissions from grazing and also to develop targeted mitigation technologies. Soil aeration, gas diffusion and drainage are key factors regulating N transformations and are affected by compaction during grazing. To understand how soil compaction from animal treading influences N transformations of urine in wet soils, we applied pressures of 0, 220 and 400 kPa to repacked soil cores, followed by ¹⁵N-labeled synthetic urine, and then subjected the cores to three successive saturation–drainage cycles on tension tables from 0 to 10 kPa.Compaction had a relatively small effect on soil bulk density (increasing from 0.81 to 0.88 Mg m⁻³), but strongly affected the pore size distribution. Compaction reduced both total soil porosity and macroporosity. It also affected the pore size distribution, principally by decreasing the proportion of 30–60 μm and 60–100 μm pores and increasing the proportion of micropores (<30 μm).Rates of urine-N transformations, emissions of N₂ and N₂O, and the N₂O to N₂ ratio were affected by the saturation/drainage cycles and degree of compaction. During the first saturation–drainage cycle, production of both N₂O and N₂ was low (<0.4 mg N m⁻² h⁻¹), probably because of anaerobic conditions inhibiting nitrification. In the second saturation/drainage cycle, the predominant product was N₂ at all compaction rates. By the third cycle, with increasing availability of mineral-N substrates, N₂O was the dominant product in the uncompacted (max = 4.70 mg N m⁻² h⁻¹) and 220 kPa compacted soils (max = 7.65 mg N m⁻² h⁻¹) with lower amounts of N₂ produced, while N₂ was produced in similar quantities to N₂O (max = 3.11 mg N m⁻² h⁻¹) in the 400 kPa compacted soil. Reduced macroporosity in the most compacted soil contributed to more sustained N₂ and N₂O production as the soils drained. In addition, compaction affected the rate of change of soil pH and DOC, both of which affected the N₂O to N₂ ratio.Denitrification during drainage and re-saturation may make a large contribution to soil N₂O emissions. Improving soil drainage and adopting grazing management practices that avoid soil compaction while increasing macroporosity will reduce total N₂O and N₂ emissions.     

Dinitrogen emissions and the N2:N2O emission ratio of a Rendzic Leptosol as influenced by pH and forest thinning

Reduction of nitrous oxide (N₂O) to dinitrogen (N₂) by denitrification in soils is of outstanding ecological significance since it is the prevailing natural process converting reactive nitrogen back into inert molecular dinitrogen. Furthermore, the extent to which N₂O is reduced to N₂ via denitrification is a major regulating factor affecting the magnitude of N₂O emission from soils. However, due to methodological problems in the past, extremely little information is available on N₂ emission and the N₂:N₂O emission ratio for soils of terrestrial ecosystems. In this study, we simultaneously determined N₂ and N₂O emissions from intact soil cores taken from a mountainous beech forest ecosystem. The soil cores were taken from plots with distinct differences in microclimate (warm-dry versus cool-moist) and silvicultural treatment (untreated control versus heavy thinning). Due to different microclimates, the plots showed pronounced differences in pH values (range: 6.3–7.3). N₂O emission from the soil cores was generally very low (2.0 ± 0.5–6.3 ± 3.8 μg N m⁻² h⁻¹ at the warm-dry site and 7.1 ± 3.1–57.4 ± 28.5 μg N m⁻² h⁻¹ at the cool-moist site), thus confirming results from field measurements. However, N₂ emission exceeded N₂O emission by a factor of 21 ± 6–220 ± 122 at the investigated plots. This illustrates that the dominant end product of denitrification at our plots and under the given environmental conditions is N₂ rather than N₂O. N₂ emission showed a huge variability (range: 161 ± 64–1070 ± 499 μg N m⁻² h⁻¹), so that potential effects of microclimate or silvicultural treatment on N₂ emission could not be identified with certainty. However, there was a significant effect of microclimate on the magnitude of N₂O emission as well as on the mean N₂:N₂O emission ratio. N₂:N₂O emission ratios were higher and N₂O emissions were lower for soil cores taken from the plots with warm-dry microclimate as compared to soil cores taken from the cool-moist microclimate plots. We hypothesize that the increase in the N₂:N₂O emission ratio at the warm-dry site was due to higher N₂O reductase activity provoked by the higher soil pH value of this site. Overall, the results of this study show that the N₂:N₂O emission ratio is crucial for understanding the regulation of N₂O fluxes of the investigated soil and that reliable estimates of N₂ emissions are an indispensable prerequisite for accurately calculating total N gas budgets for the investigated ecosystem and very likely for many other terrestrial upland ecosystems as well.     

Nitrous oxide emissions from fertilized,irrigated cotton (Gossypium hirsutum L.) in the Aral Sea Basin,Uzbekistan: Influence of nitrogen applications and irrigation practices

Nitrous oxide emissions were monitored at three sites over a 2-year period in irrigated cotton fields in Khorezm, Uzbekistan, a region located in the arid deserts of the Aral Sea Basin. The fields were managed using different fertilizer management strategies and irrigation water regimes. N₂O emissions varied widely between years, within 1 year throughout the vegetation season, and between the sites. The amount of irrigation water applied, the amount and type of N fertilizer used, and topsoil temperature had the greatest effect on these emissions.Very high N₂O emissions of up to 3000 μg N₂O-N m^?2 h^?1 were measured in periods following N-fertilizer application in combination with irrigation events. These “emission pulses” accounted for 80–95% of the total N₂O emissions between April and September and varied from 0.9 to 6.5 kg N₂O-N ha^?1.. Emission factors (EF), uncorrected for background emission, ranged from 0.4% to 2.6% of total N applied, corresponding to an average EF of 1.48% of applied N fertilizer lost as N₂O-N. This is in line with the default global average value of 1.25% of applied N used in calculations of N₂O emissions by the Intergovernmental Panel on Climate Change.During the emission pulses, which were triggered by high soil moisture and high availability of mineral N, a clear diurnal pattern of N₂O emissions was observed, driven by daily changes in topsoil temperature. For these periods, air sampling from 8:00 to 10:00 and from 18:00 to 20:00 was found to best represent the mean daily N₂O flux rates. The wet topsoil conditions caused by irrigation favored the production of N₂O from NO₃^? fertilizers, but not from NH₄⁺ fertilizers, thus indicating that denitrification was the main process causing N₂O emissions. It is therefore argued that there is scope for reducing N₂O emission from irrigated cotton production; i.e. through the exclusive use of NH₄⁺ fertilizers. Advanced application and irrigation techniques such as subsurface fertilizer application, drip irrigation and fertigation may also minimize N₂O emission from this regionally dominant agro-ecosystem.     

Nitrous oxide emissions from a rainfed-cultivated black soil in Northeast China: effect of fertilization and maize crop

Nitrous oxide emission (N₂O) from applied fertilizer across the different agricultural landscapes especially those of rainfed area is extremely variable (both spatially and temporally), thus posing the greatest challenge to researchers, modelers, and policy makers to accurately predict N₂O emissions. Nitrous oxide emissions from a rainfed, maize-planted, black soil (Udic Mollisols) were monitored in the Harbin State Key Agroecological Experimental Station (Harbin, Heilongjiang Province, China). The four treatments were: a bare soil amended with no N (C0) or with 225?kg?N ha^?1 (CN), and maize (Zea mays L.)-planted soils fertilized with no N (P0) or with 225?kg?N ha^?1 (PN). Nitrous oxide emissions significantly (P?<?0.05) increased from 141?±?5?g N₂O-N?ha^?1 (C0) to 570?±?33?g N₂O-N?ha^?1 (CN) in unplanted soil, and from 209?±?29?g N₂O-N?ha^?1 (P0) to 884?±?45?g N₂O-N?ha^?1 (PN) in planted soil. Approximately 75?% of N₂O emissions were from fertilizer N applied and the emission factor (EF) of applied fertilizer N as N₂O in unplanted and planted soils was 0.19 and 0.30?%, respectively. The presence of maize crop significantly (P?<?0.05) increased the N₂O emission by 55?% in the N-fertilized soil but not in the N-unfertilized soil. There was a significant (P?<?0.05) interaction effect of fertilization?×?maize on N₂O emissions. Nitrous oxide fluxes were significantly affected by soil moisture and soil temperature (P?<?0.05), with the temperature sensitivity of 1.73–2.24, which together explained 62–76?% of seasonal variation in N₂O fluxes. Our results demonstrated that N₂O emissions from rainfed arable black soils in Northeast China primarily depended on the application of fertilizer N; however, the EF of fertilizer N as N₂O was low, probably due to low precipitation and soil moisture.     

Crop residues and fertilizer nitrogen influence residue decomposition and nitrous oxide emission from a Vertisol

Crop residues with high C/N ratio immobilize N released during decomposition in soil, thus reducing N losses through leaching, denitrification, and nitrous oxide (N₂O) emission. A laboratory incubation experiment was conducted for 84 days under controlled conditions (24°C and moisture content 55% of water-holding capacity) to study the influence of sugarcane, maize, sorghum, cotton and lucerne residues, and mineral N addition, on N mineralization–immobilization and N₂O emission. Residues were added at the rate of 3 t C ha⁻¹ to soil with, and without, 150 kg urea N ha⁻¹. The addition of sugarcane, maize, and sorghum residues without N fertilizer resulted in a significant immobilization of soil N. Amended soil had significantly (P < 0.05) lower NO₃⁻–N, which reached minimum values of 2.8 mg N kg⁻¹ for sugarcane (at day 28), 10.3 mg N kg⁻¹ for maize (day 7), and 5.9 mg N kg⁻¹ for sorghum (day 7), compared to 22.7 mg N kg⁻¹ for the unamended soil (day 7). During 84 days of incubation, the total mineral N in the residues + N treatments were decreased by 45 mg N kg⁻¹ in sugarcane, 34 mg kg⁻¹ in maize, 29 mg kg⁻¹ in sorghum, and 16 mg kg⁻¹ in cotton amended soil compared to soil + N fertilizer, although soil NO₃⁻–N increased by 7 mg kg⁻¹ in lucerne amended soil. The addition of residues also significantly increased amended soil microbial biomass C and N. Maximum emissions of N₂O from crop residue amended soils occurred in the first 4–5 days of incubation. Overall, after 84 days of incubation, the cumulative N₂O emission was 25% lower with cotton + N fertilizer, compared to soil + N fertilizer. The cumulative N₂O emission was significantly and positively correlated with NO₃⁻–N (r = 0.92, P < 0.01) and total mineral N (r = 0.93, P < 0.01) after 84 days of incubation, and had a weak but significant positive correlation with cumulative CO₂ in the first 3 and 5 days of incubation (r = 0.59, P < 0.05).     

Nitrous oxide and methane emissions from grassland treated with bark- or sawdust-containing manure at different rates

On the main Japanese island of Honshu, bark or sawdust is often added to cattle excreta as part of the composting process. Dairy farmers sometimes need to dispose of manure that is excess to their requirements by spreading it on their grasslands. We assessed the effect of application of bark- or sawdust-containing manure at different rates on annual nitrous oxide (N₂O) and methane (CH₄) emissions from a grassland soil. Nitrous oxide and CH₄ fluxes from an orchardgrass (Dactylis glomerata L.) grassland that received this manure at 0, 50, 100, 200, or 300?Mg?ha^?1?yr^?1 were measured over a two-year period by using closed chambers. Two-way analysis of variance (ANOVA) was employed to examine the effect of annual manure application rates and years on annual N₂O and CH₄ emissions. Annual N₂O emissions ranged from 0.47 to 3.03?kg?N?ha^?1?yr^?1 and increased with increasing manure application rate. Nitrous oxide emissions during the 140-day period following manure application increased with increasing manure application rate, with the total nitrogen concentration in the manure, and with cumulative precipitation during the 140-day period. However, manure application rate did not affect the N₂O emission factors of the manure. The overall average N₂O emission factor was 0.068%. Annual CH₄ emissions ranged from ?1.12 to 0.01?kg?C?ha^?1?yr^?1. The annual manure application rate did not affect annual CH₄ emissions.     

Contributions from different microbial processes to N2O emission from soil under different moisture regimes

Nitrous oxide emissions from a sandy-loam textured soil wetted to matric potentials of either-1.0 or-0.1 kPa were determined in laboratory experiments in which the soil was incubated in air (control), air plus 10 Pa C₂H₂ (to inhibit nitrification), 100 kPa O₂ (to suppress denitrification), 10 kPa C₂H₂ (to inhibit N₂O reduction to N₂ in denitrification) or following autoclaving. The total N₂O production, consumption and net N₂O emission from the soils together with the contributions to N₂O emission from different processes of N₂O production were estimated. The rate of N₂O production was significantly greater in the wetter soil (282 pmol N₂O g^-1 soil h^-1) than in the drier soil (192 pmol N₂O g^-1 soil h^-1), but because N₂O consumption by denitrifiers was also greater in the wetter soil, the net N₂O emissions from the wetter and the drier soils did not differ significantly. Non-biological sources made no significant contribution to N₂O emission under either moisture regime and biological processes other than denitrification and nitrification made only a small contribution (1% of the total N₂O production) in the wetter soil. Denitrifying nitrifiers were the predominant source of N₂O emitted from the drier soil and other (non-nitrifying) denitrifiers were the predominant source of N₂O emitted from the wetter soil.