Grazing effects on the greenhouse gas balance of a temperate steppe ecosystem

Although a significant fraction of the global soil?Catmosphere exchange of greenhouse gases (GHGs) occurs in semi-arid zones little is known about the magnitude of fluxes in grazed steppe ecosystems and the interference with grazing intensity. In order to assess GHG burdens and to identify options of climate-optimized livestock farming, GHG emissions of sheep grazing in Inner Mongolia steppe were analyzed. Carbon sequestration and field-fluxes of methane (CH₄) and nitrous oxide (N₂O) were measured at a range of steppe sites differing in grazing intensity and management, i.e. ungrazed (UG), ungrazed with hay cutting (HC), lightly grazed (LG), moderately grazed (MG), and heavily grazed (HG). In addition, GHG emissions from enteric fermentation, manure management, and farming inputs (i.e. fossil fuels) were quantified for LG, MG, and HG. Monte Carlo simulation was used to estimate uncertainty. Sheep grazing changed the net GHG balance of the steppe from a significant sink at UG (?1476?±?2481?kg CO_2eq ha^?1?year^?1) to a significant source at MG (2350?±?1723?kg CO_2eq ha^?1?year^?1) and HG (3115?±?2327?kg CO_2eq ha^?1?year^?1). In a similar way, the GHG intensity increased from 8.6?±?79.2?kg CO_2eq?kg^?1 liveweight gain at LG up to 62.2?±?45.8 and 62.6?±?46.7?kg CO_2eq?kg^?1 liveweight gain at MG and HG, respectively. GHG balances were predominantly determined by CO₂ from changes in topsoil organic carbon. In grazing systems, CH₄ from enteric fermentation was the second most important component. The results suggest that sheep grazing under the current management changes this steppe ecosystem from a sink to a source of GHGs and that grazing exclusion holds large potential to restore soil organic carbon stocks and thus to sequester atmospheric CO₂. The balance between grazing intensity and grazing exclusion predominantly determines GHG balances of grass-based sheep farming in this region. Therefore, a high proportion of ungrazed land is most important for reducing GHG balances of sheep farms. This can be either achieved by high grazing intensity on the remaining grazed land or by confined hay feeding of sheep.     

Methane emissions from a rice agroecosystem in South China: Effects of water regime, straw incorporation and nitrogen fertilizer

To quantitatively assess the effects of agricultural practices on methane (CH₄) emissions from rice fields, a two-year (2005/2006) field experiment with 2³ factorial designs was conducted to assess the effects of three driving factors on CH₄ emissions in South China: continuously flooded (W0) and mid-season and final drainages (W2), straw (S1) and nitrogen fertilizer (N1) applications and their controls (S0, N0). Results showed that averaged across all the treatments about 75?% of the seasonal total CH₄ occurred between the rice transplanting and booting stage, while constituted only 33?% of the seasonal total rice biomass during the same period. Averaged across the treatments in 2006, CH₄ emissions were substantially decreased by mid-season drainage up to 60?% (15.6 vs. 39.0?g?m^?2). The decreased CH₄ emissions represented almost all of the decrease in the total global warming potentials. Without straw incorporation CH₄ emissions substantially decreased up to 59?% (15.9 vs. 38.7?g?m^?2). The stimulating effects of straw were significantly greater for W0 than W2 treatment, being also greater in the 2005 than in the 2006 season. A significant inter-annual difference in CH₄ emissions was found when averaged across straw incorporation and N fertilizer applications for the W2 treatment (42.8 and 15.4?g?m^?2 in 2005 and 2006, respectively). Moreover, N fertilization has no significant effect on CH₄ emissions in this study. Our results demonstrate that although straw effects varied greatly with specific management, both straw managements and water regimes are equally important driving factors and thus being the most promising measures attenuating CH₄ emissions while achieving sustainable rice production.     

Greenhouse gas intensity and net annual global warming potential of cotton cropping systems in an extremely arid region

A long-term fertilizer experiment investigating cotton-based cropping systems established in 1990 in central Asia was used to quantify the emissions of CO₂, CH₄ and N₂O from April 2012 to April 2013 to better understand greenhouse gas (GHG) emissions and net global warming potential (GWP) in extremely arid croplands. The study involved five treatments: no fertilizer application as a control (CK), balanced fertilizer NPK (NPK), fertilizer NPK plus straw (NPKS), fertilizer NPK plus organic manure (NPKM), and high rates of fertilizer NPK and organic manure (NPKM+). The net ecosystem carbon balance was estimated by the changes in topsoil (0–20 cm) organic carbon (SOC) density over the 22-year period 1990–2012. Manure and fertilizer combination treatments (NPKM and NPKM+) significantly increased CO₂ and slightly increased N₂O emissions during and outside the cotton growing seasons. Neither NPK nor NPKS treatment increased SOC in spite of relatively low CO₂, CH₄ and N₂O fluxes. Treatments involving manure application showed the lowest net annual GWP and GHG intensity (GHGI). However, overuse of manure and fertilizers (NPKM+) did not significantly increase cotton yield (5.3 t ha^?1) but the net annual GWP (?4,535 kg CO₂_eqv. ha^?1) and GHGI (?0.86 kg CO₂_eqv. kg^?1 grain yield of cotton) were significantly lower than in NPKM. NPKS and NPK slightly increased the net annual GWP compared with the control plots. Our study shows that a suitable rate of fertilizer NPK plus manure may be the optimum choice to increase soil carbon sequestration, maintain crop yields, and restrict net annual GWP and GHGI to relatively low levels in extremely arid regions.     

Integrated management practices significantly affect N2O emissions and wheat–maize production at field scale in the North China Plain

In the North China Plain, a field experiment was conducted to measure nitrous oxide (N₂O) and methane (CH₄) fluxes from a typical winter wheat–summer maize rotation system under five integrated agricultural management practices: conventional regime [excessive nitrogen (N) fertilization, flood irrigation, and rotary tillage before wheat sowing; CON], recommended regime 1 (balanced N fertilization, decreased irrigation, and deep plowing before wheat sowing; REC-1), recommended regime 2 (balanced N fertilization, decreased irrigation, and no tillage; REC-2), recommended regime 3 (controlled release N fertilizer, decreased irrigation, and no tillage; REC-3), and no N fertilizer (CK). Field measurements indicated that pulse emissions after N fertilization and irrigation contributed 19–49 % of annual N₂O emissions. In contrast to CON (2.21 kg N₂O-N ha^?1 year^?1), the other treatments resulted in significant declines in cumulative N₂O emissions, which ranged from 0.96 to 1.76 kg N₂O-N ha^?1 year^?1, indicating that the recommended practices (e.g., balanced N fertilization, controlled release N fertilizer, and decreased irrigation) offered substantial benefits for both sustaining grain yield and reducing N₂O emissions. Emission factors of N fertilizer were 0.21, 0.22, 0.23, and 0.37 % under CON, REC-1, REC-3, and REC-2, respectively. Emissions of N₂O during the freeze–thaw cycle period and the winter freezing period accounted for 9.7 and 5.1 % of the annual N₂O budget, respectively. Thus, we recommend that the monitoring frequency should be increased during the freeze–thaw cycle period to obtain a proper estimate of total emissions. Annual CH₄ fluxes from the soil were low (?1.54 to ?1.12 kg CH₄-C ha^?1 year^?1), and N fertilizer application had no obvious effects on CH₄ uptake. Values of global warming potential were predominantly determined by N₂O emissions, which were 411 kg CO₂-eq ha^?1 year^?1 in the CK and 694–982 kg CO₂-eq ha^?1 year^?1 in the N fertilization regimes. When comprehensively considering grain yield, global warming potential intensity values in REC-1, REC-2, and REC-3 were significantly lower than in CON. Meanwhile, grain yield increased slightly under REC-1 and REC-3 compared to CON. Generally, REC-1 and REC-3 are recommended as promising management regimes to attain the dual objectives of sustaining grain yield and reducing greenhouse gas emissions in the North China Plain.     

Soil organic matter,greenhouse gases and net global warming potential of irrigated conventional,reduced-tillage and organic cropping systems

Reducing tillage intensity and diversifying crop rotations may improve the sustainability of irrigated cropping systems in semi-arid regions. The objective of this study was to compare the greenhouse gas (GHG) emissions, soil organic matter, and net global warming potential (net GWP) of a sugar beet (Beta vulgaris L.)-corn (Zea mays L,) rotation under conventional (CT) and reduced-tillage (RT) and a corn-dry bean (Phaseolus vulgaris L.) rotation under organic (OR) management during the third and fourth years of 4-year crop rotations. The gas and soil samples were collected during April 2011–March 2013, and were analyzed for carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) emissions, water-filled pore space (WFPS), soil nitrate (NO₃ ^?–N) and ammonium (NH₄ ⁺–N) concentrations, soil organic carbon (SOC) and total nitrogen (TN), and net global warming potential (net GWP). Soils under RT had 26% lower CO₂ emissions compared to 10.2 kg C ha^?1 day^?1 and 43% lower N₂O emissions compared to 17.5 g N ha^?1 day^?1 in CT during cropping season 2011, and no difference in CO₂ and N₂O emissions during cropping season 2012. The OR emitted 31% less N₂O, but 74% more CO₂ than CT during crop season 2011. The RT had 34% higher SOC content than CT (17.9 Mg ha^?1) while OR was comparable with CT. Net GWP was negative for RT and OR and positive for CT. The RT and OR can increase SOC sequestration, mitigate GWP and thereby support in the development of sustainable cropping systems in semiarid agroecosystems.     

Effects of Elevated CO2 and Temperature on Methane Production and Emission from Submerged Soil Microcosm

Incubation experiments were conducted under controlled laboratory conditions to study the interactive effects of elevated carbon dioxide (CO₂) and temperature on the production and emission of methane (CH₄) from a submerged rice soil microcosm. Soil samples (unamended soil; soil + straw; soil + straw + N fertilizer) were placed in four growth chambers specifically designed for a combination of two levels of temperature (25 °C or 35 °C) and two levels of CO₂ concentration (400 or 800 mol mol^–1) with light intensity of about 3000 Lx for 16 h d^–1. At 7, 15, 30, and 45 d after incubation, CH₄ flux, CH₄ dissolved in floodwater, subsurface soil-entrapped CH₄, and CH₄ production potential of the subsurface soil were determined. The results are summarized as follows: 1) The amendment with rice straw led to a severalfold increase in CH₄ emission rates, especially at 35 °C. However, the CH₄ flux tended to decrease considerably after 15 d of incubation under elevated CO₂. 2) The amount of entrapped CH₄ in subsurface soil and the CH₄ production potential of the subsurface soil were appreciably larger in the soil samples incubated under elevated CO₂ and temperature during the early incubation period. However, after 15 d, they were similar in the soil samples incubated under elevated or ambient CO₂ levels. These results clearly indicated that elevated CO₂ and temperature accelerated CH₄ formation by the addition of rice straw, while elevated CO₂ reduced CH₄ emission at both temperatures.     

Algorithms for calculating methane and nitrous oxide emissions from manure management

Biogenic emissions of methane (CH₄) and nitrous oxide (N₂O) from animal manure are stimulated by the degradation of volatile solids (VS) which serves as an energy source and a sink for atmospheric oxygen. Algorithms are presented which link carbon and nitrogen turnover in a dynamic prediction of CH₄ and N₂O emissions during handling and use of liquid manure (slurry). A sub-model for CH₄ emissions during storage relates CH₄ emissions to VS, temperature and storage time, and estimates the reduction in VS. A second sub-model estimates N₂O emissions from field-applied slurry as a function of VS, slurry N and soil water potential, but emissions are estimated using emission factors. The model indicated that daily flushing of slurry from cattle houses would reduce total annual CH₄ + N₂O emissions by 35% (CO₂ eq.), and that cooling of pig slurry in-house would reduce total annual CH₄ + N₂O emissions by 21% (CO₂ eq.). Anaerobic digestion of slurry and organic waste produces CH₄ at the expense of VS. Accordingly, the model predicted a 90% reduction of CH₄ emissions from outside stores with digested slurry, and a >50% reduction of N₂O emissions after spring application of digested as opposed to untreated slurry. The sensitivity of the model towards storage temperature and soil water potential was examined. This study indicates that simple algorithms to account for ambient climatic conditions may significantly improve the prediction of CH₄ and N₂O emissions from animal manure.     

Integrating beef cattle on cropland affects net global warming potential

Recent interest in integrated crop-livestock (ICL) systems has prompted numerous investigations to quantify ecosystem service tradeoffs associated with management. However, few investigations have quantified ICL management effects on net global warming potential (GWP), particularly in semiarid regions. Therefore, we determined net GWP for grazed and ungrazed cropland in a long-term ICL study near Mandan, ND USA. Factors evaluated for their contribution to net GWP included carbon dioxide (CO₂) emissions associated with production inputs and field operations, methane (CH₄) emissions from enteric fermentation by beef cattle, change in soil carbon stocks, and soil-atmosphere CH₄ and nitrous oxide (N₂O) fluxes. Net GWP was significantly greater for grazed cropland (946 kg CO_2equiv. ha^-1 yr^-1) compared to ungrazed cropland (200 kg CO_2equiv. ha^-1 yr^-1) (P=0.0331). The difference in net GWP between treatments was largely driven by emissions from enteric fermentation (602 kg CO_2equiv. ha^-1 yr^-1). Among other contributing factors, CO₂ emissions associated with seed production and field operations were lower under ungrazed cropland (P?=?0.0015 and 0.0135, respectively), while soil CH₄ uptake was greater under grazed cropland (P?=?0.0102). Soil-atmosphere N₂O flux from each system negated nearly all the CO_2equiv. sink capacity accrued from soil carbon stock change. As both production systems resulted in net greenhouse gas (GHG) emissions to the atmosphere, novel practices that constrain GHG sources and boost GHG sinks under semiarid conditions are recommended.

     

Impact of agriculture on soil consumption of atmospheric CH4 and a comparison of CH4 and N2O flux in subarctic, temperate and tropical grasslands

Increasing concentrations of methane (CH₄) in the atmosphere are projected to account for about 25% of the net radiative forcing. Biospheric emissions of CH₄ to the atmosphere total approximately 400 Tg C y^-1. An estimated 300 Tg of CH₄-C y^-1 is oxidized in the atmosphere by hydroxyl radicals while about 40 Tg y^-1 remains in the atmosphere. Approximately 40 Tg y^-1 of the atmospheric burden is oxidized in aerobic soils. Research efforts during the past several years have focused on quantifying CH₄ sources while relatively less effort has been directed toward quantifying and understanding the soil sink for atmospheric CH₄. Recent research has demonstrated that land use change, including agricultural use of native forest and grassland systems has decreased the soil sink for atmospheric methane. Some agricultural systems consume atmospheric CH₄ at rates less than 10% of those found in comparable undisturbed soils. While it has been necessary to change land use practices over the past centuries to meet the required production of food and fiber, we need to recognize and account for impacts of land use change on the biogeochemical nutrient cycles in the biosphere. Changes that have ensued in these cycles have and will impact the atmospheric concentrations of CH₄ and N₂O. Since CH₄ and N₂O production and consumption are accomplished by a variety of soil microorganisms, the influence of changing agricultural, forest, and, demographic patterns has been large. Existing management and technological practices may already exist to limit the effect of land use change and agriculture on trace gas fluxes. It is therefore important to understand how management and land use affect trace gas fluxes and to observe the effect of new technology on them. This paper describes the role of aerobic soils in the global CH₄ budget and the impact of agriculture on this soil CH₄ sink. Examples from field studies made across subarctic, temperate and tropical climate gradients in grasslands are used to demonstrate the influence of nutrient cycle perturbations on the soil consumption of atmospheric CH₄ and in increased N₂O emissions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Assessment of CH4 and N2O fluxes in a Danish beech (Fagus sylvatica) forest and an adjacent N-fertilised barley (Hordeum vulgare) field: effects of sewage sludge amendments

Fluxes of CH₄ and N₂O were measured regularly in an agricultural field treated with 280 g m⁻² of sewage sludge. In a nearby beech forest N₂O and CH₄ fluxes were measured in a well-drained (dry) area and in a wet area adjacent to a drainage canal. We observed brief increases of both CH₄ and N₂O emissions immediately following soil applications of digested sewage sludge. Cumulated values for CH₄ emissions over the course of 328 days after sludge applications indicated a small net source in sludge treated plots (7.6 mg C m⁻²) whereas sludge-free soil constituted a small sink (-0.9 mg C m⁻²). The CH₄ emission amounted 0.01% of the sludge-C. Extrapolated to current rates of sludge applications in Danish agriculture this amounts to 0.1% of the total agricultural derived CH₄. Sludge applications did not affect cumulated fluxes of N₂O showing 312 mg N₂O–N m⁻² and 304 mg N m⁻² with and without sludge, respectively. Four months after the sludge applications a significant effect on CO₂ and NO emissions was still obvious in the field, the latter perhaps due to elevated nitrification. Nitrous oxide emission in the beech forest was about six times smaller (45 mg N m⁻²) than in the field and independent of drainage status. Methane oxidation was observed all-year round in the forest cumulating to -225 mg C m⁻² and -84 mg C m⁻² in dry and wet areas. In a model experiment with incubated soil cores, nitrogen amendment (NH₄Cl) and perturbation significantly reduced CH₄ oxidation in the forest soil, presumably as a result of increased nitrification activity. Sludge also induced net CH₄ production in the otherwise strong CH₄ oxidising forest soil. This emphasises the potential for CH₄ emissions from sewage sludge applications onto land. The study shows, however, that emissions of N₂O and CH₄ induced by sewage sludge in the field is of minor importance and that factors such as land use (agriculture versus forest) is a much stronger controller on the source/sink strengths of CH₄ and N₂O. This revised version was published online in August 2006 with corrections to the Cover Date.     

Emissions of CH4, N2O, NH3 and odorants from pig slurry during winter and summer storage

Manure storage contributes significantly to greenhouse gas (GHG), NH₃ and odour emissions from intensive livestock production. A pilot-scale facility with eight 6.5-m³ slurry storage units was used to quantify emissions of CH₄, N₂O, NH₃, and odorants from pig slurry during winter and summer storage. Pig slurry was stored with or without a straw crust, and with or without interception of precipitation, i.e., four treatments, in two randomized blocks. Emissions of total reduced S (mainly H₂S) and p-cresol, but not skatole, were reduced by the straw crust. Total GHG emissions were 0.01–0.02 kg CO₂ eq m^?3 day^?1 during a 45-day winter storage, and 1.1–1.3 kg CO₂ eq m^?3 day^?1 during a 58-day summer storage period independent of storage conditions; the GHG balance was dominated by CH₄ emissions. Nitrous oxide emissions occurred only during summer storage where, apparently, emissions were related to the water balance of the surface crust. An N₂O emission factor for slurry storage with a straw crust was estimated at 0.002–0.004. There was no evidence for a reduction of CH₄ emissions with a crust. Current Intergovernmental Panel on Climate Change recommendations for N₂O and CH₄ emission factors are discussed.     

Greenhouse gas emissions from soil under maize–soybean intercrop in the North China Plain

Intercrop systems can exhibit unique soil properties compared to monocultures, which influences the microbially-mediated processes leading to greenhouse gas emissions. Fertilized intercrops and monocultures produce different amounts of N₂O, CO₂ and CH₄ depending on their nutrient and water use efficiencies. The objective of this study was to compare the fluxes and seasonal emissions of N₂O, CO₂, and CH₄ from a maize–soybean intercrop compared to maize and soybean monocultures, in relation to crop effects on soil properties. The experiment was conducted during 2012, 2013 and 2014 at the WuQiao Experimental Station in the North China Plain. All cropping systems received urea-N fertilizer (240 kg N ha^?1 applied in two split applications). The cropping systems were a net source of CO₂ and a net sink of CH₄, with significantly (P < 0.05 in 2012) and numerically (2013 and 2014) lower N₂O flux and smaller seasonal N₂O emissions from the maize–soybean intercrop than the maize monoculture. The proportion of urea-N lost as N₂O was lower in the maize–soybean intercrop (1.6% during the 3-year study) and soybean monoculture (1.7%), compared to maize monoculture (2.3%). Soybean reduced the soil NO₃^?–N concentration and created a cooler, drier environment that was less favorable for denitrification, although we cannot rule out the possibility of N₂O reduction to N₂ and other N compounds by soybean and its associated N₂-fixing prokaryotes. We conclude that maize–soybean intercrop has potential to reduce N₂O emissions in fertilized agroecosystems and should be considered in developing climate-smart cropping systems in the North China Plain.     

Annual vegetation burns across the northern savanna region of Ghana: period of occurrence, area burns, nutrient losses and emissions

This study has assessed the seasonal occurrence of annual vegetation fires and defined inter-seasonally burned area for the different vegetation cover types across Ghana and the northern region of Ghana using 10-year (2001?C2010) remote sensing data. These values were used with fire induced elemental losses to estimate greenhouse gas emissions and net plant nutrient loss due to gross bush fire nutrient transfers and annual atmospheric nutrient depositions. About 21, 68, 10 and 1?% of annual burns across the northern region of Ghana take place in the months of November, December, January and February respectively. As much as 68?±?4 thousand km² (25?C32?%) and 37?±?2.6 thousand km² (46?C60?%) of dry land are annually burned across Ghana and the northern region of Ghana respectively, with 53?C56?% of the total annual burns across the country taking place in the northern region. About 10,100?C28,400 Gg of C, comprising 215?C4,700 thousand Gg of CO₂ equivalent (CO₂, CH₄) potential global warming green house gases and 48?C324 thousand Gg of local pollutants (CO, NO_x) are estimated to be released annually through bush fire occurrence across Ghana. Net negative balance for P between fire-induced nutrient transfers and, annual wet and dry nutrient deposits is of concern given the high P-sorbing mineral content of the soils. The temporal loss of P suggest an input source than wet and dry atmospheric P depositions for the sustenance of the ecosystem or predict a long term threat to regional food production.     

Methane uptake by saline–alkaline soils with varying electrical conductivity in the Hetao Irrigation District of Inner Mongolia,China

Soil salinization adversely affects sustainable land use and limitation of greenhouse gas emission. Methane (CH₄) uptake and the specific activity of methanotrophs in three saline–alkaline soils—S1, electrical conductivity (EC) 4.80?dS?m^?1; S2, EC 2.60?dS?m^?1; and S3, EC 0.74?dS?m^?1—were observed and measured across crop phenological development in the Hetao Irrigation District of Inner Mongolia, China. There were significant differences in CH₄ uptake between the three soil types. The cumulative uptake of CH₄ was 97.97 mg m^?2, 109.49 mg m^?2, and 150.0 mg m^?2 in S1, S2, and S3, respectively. Cumulative CH₄ uptake was 35%, 35%, and 53% lower in S1 than in S3, and was 27%, 28%, and 19% lower in S2 than in S3 in 2014, 2015, and 2016, respectively. Differences in CH₄ uptake were driven by the different specific activities of the methanotrophs in the three soils, of which the key controlling factor was soil EC. The findings demonstrate that saline–alkaline soils with high EC led to low CH₄ uptake and thereby significantly increased the total greenhouse effect of CH₄.     

Greenhouse gas emissions from tropical peatlands of Kalimantan,Indonesia

Greenhouse gas emissions were measured from tropical peatlands of Kalimantan, Indonesia. The effect of hydrological zone and land-use on the emission of N₂O, CH₄ and CO₂ were examined. Temporal and annual N₂O, CH₄ and CO₂ were then measured. The results showed that the emissions of these gases were strongly affected by land-use and hydrological zone. The emissions exhibited seasonal changes. Annual emission of N₂O was the highest (nearly 1.4 g N m^–2y^–1) from site A-1 (secondary forest), while there was no signi.cant difference in annual N₂O emission from site A-2 (paddy field) and site A-3 (rice-soybean rotation field). Multiplying the areas of forest and non-forest in Kalimantan with the emission of N₂O from corresponding land-uses, the annual N₂O emissions from peat forest and peat non-forest of Kalimantan were estimated as 0.046 and 0.004 Tg N y^–1, respectively. The emissions of CH₄ from paddy field and non-paddy field were estimated similarly as 0.14 and 0.21 Tg C y^–1, respectively. Total annual CO₂ emission was estimated to be 182 Tg C y^–1. Peatlands of Kalimantan, Indonesia, contributed less than 0.3 of the total global N₂O, CO₂ or CH₄ emission, indicating that the gaseous losses of soil N and C from the study area to the atmosphere were small.     

Gross mineralization, nitrification and N2O emission under different tillage in the North China Plain

No-tillage cropping can increase soil carbon (C) stocks and aggregation, and subsequently impact the internal nitrogen (N) cycle and gas loss. The ¹⁵N pool dilution method was used to study gross N transformations, and relative proportions of nitrous oxide (N₂O) emissions derived from denitrification versus nitrification-related processes under long-term tillage systems (no-tillage, rotary tillage and conventional tillage) in the North China Plain. In-field incubation experiments were repeated in successive growing seasons during April?CNovember in 2007. Gross mineralization rates for rotary and mouldboard plough tillage (3.6?±?0.3?C10.6?±?1.5?mg?N?kg^?1?days^?1) were significantly higher than for no-tillage (1.7?±?0.8?C6.8?±?1.1?mg?N?kg^?1?days^?1). Gross mineralization was positively correlated with soil moisture and temperature, as well as with microbial biomass N and C. However, there was no consistent tillage effect on gross nitrification, and gross nitrification was positively correlated with soil moisture, but not with gross mineralization and microbial biomass. N₂O emissions were higher in no-tillage (NT) than for conventional tillage (CT) during May?CAugust. The ¹⁵N labelling indicated that 26?C92?% of the N₂O was directly derived from the soil ammonium (NH₄ ⁺) pool. Emission rates of N₂O from both nitrification and denitrification were positively correlated with NH₄ ⁺ supply as expressed by gross mineralization, but not correlated with supply of nitrate as expressed by gross nitrification. The fraction of nitrified N emitted as N₂O was positively correlated with changes in soil moisture and varied within 0.01?C2.51???. Our results showed that the tillage management impact on gross N transformation was not consistent with N₂O emission, and more detailed information on the controls over N₂O formation needs to be sought.     

Nitrous oxide and methane emissions from cultivated seasonal wetland (dambo) soils with inorganic,organic and integrated nutrient management

In many smallholder farming areas southern Africa, the cultivation of seasonal wetlands (dambos) represent an important adaptation to climate change. Frequent droughts and poor performance of rain-fed crops in upland fields have resulted in mounting pressure to cultivate dambos where both organic and inorganic amendments are used to sustain crop yields. Dambo cultivation potentially increases greenhouse gas (GHG) emissions. The objective of the study was to quantify the effects of applying different rates of inorganic nitrogen (N) fertilisers (60, 120, 240 kg N ha^?1) as NH₄NO₃, organic manures (5,000, 10,000 and 15,000 kg ha^?1) and a combination of both sources (integrated management) on GHG emissions in cultivated dambos planted to rape (Brassica napus). Nitrous oxide (N₂O) emissions in plots with organic manures ranged from 218 to 894 µg m^?2 h^?1, while for inorganic N and integrated nutrient management, emissions ranged from 555 to 5,186 µg m^?2 h^?1 and 356–2,702 µg m^?2 h^?1 respectively. Cropped and fertilised dambos were weak sources of methane (CH₄), with emissions ranging from ?0.02 to 0.9 mg m^?2 h^?1, while manures and integrated management increased carbon dioxide (CO₂) emissions. However, crop yields were better under integrated nutrient management. The use of inorganic fertilisers resulted in higher N₂O emission per kg yield obtained (6–14 g N₂O kg^?1 yield), compared to 0.7–4.5 g N₂O kg^?1 yield and 1.6–4.6 g N₂O kg^?1 yield for organic manures and integrated nutrient management respectively. This suggests that the use of organic and integrated nutrient management has the potential to increase yield and reduce yield scaled N₂O emissions.     

Quantifying the Reduction of Greenhouse Gas Emissions as a Resultof Composting Dairy and Beef Cattle Manure

Greenhouse gas emissions from the agricultural sector can be reduced through implementation of improved management practices. For example, the choice of manure storage method should be based on environmental decision criteria, as well as production capacity. In this study, greenhouse gas emissions from three methods of storing dairy and beef cattle manure were compared during the summer period. The emissions of CH₄, N₂O and CO₂ from manure stored as slurry, stockpile, and compost were measured using a flow-through closed chamber. The largest combined N₂O–CH₄ emissions in CO₂ equivalent were observed from the slurry storage, followed by the stockpile and lastly the passively aerated compost. This ranking was governed by CH₄ emissions in relation to the degree of aerobic conditions within the manure. The radiative forcing in CO₂ equivalent from the stockpiled manure was 1.46 times higher than from the compost for both types of cattle manure. It was almost twice as high from the dairy cattle manure slurry and four to seven times higher from the beef cattle manure slurry than from the compost. The potential reduction of GHG was estimated, by extrapolating the results of the study to all of Canada. By composting all the cattle manure stored as slurry and stockpile, a reduction of 0.70 Tg CO₂-eq year⁻¹ would be achieved. Similarly, by collecting and burning CH₄ emissions from existing slurry facilities, a reduction of 0.76 Tg CO₂-eq year⁻¹ would be achieved. New CH₄ emission factors were estimated based on these results and incorporated into the IPCC methodology. For North-America under cool conditions, the CH₄ emission factors would be 45 kg CH₄ hd⁻¹ year⁻¹ for dairy cattle manure rather than 36 kg CH₄ hd⁻¹ year⁻¹, and 3 kg CH₄ hd⁻¹ year⁻¹ for beef cattle manure rather than 1 kg CH₄ hd⁻¹ year⁻¹.     

Soil N2O and CO2 emissions from cotton in Australia under varying irrigation management

Irrigation is known to stimulate soil microbial carbon and nitrogen turnover and potentially the emissions of nitrous oxide (N₂O) and carbon dioxide (CO₂). We conducted a study to evaluate the effect of three different irrigation intensities on soil N₂O and CO₂ fluxes and to determine if irrigation management can be used to mitigate N₂O emissions from irrigated cotton on black vertisols in South-Eastern Queensland, Australia. Fluxes were measured over the entire 2009/2010 cotton growing season with a fully automated chamber system that measured emissions on a sub-daily basis. Irrigation intensity had a significant effect on CO₂ emission. More frequent irrigation stimulated soil respiration and seasonal CO₂ fluxes ranged from 2.7 to 4.1 Mg-C ha^?1 for the treatments with the lowest and highest irrigation frequency, respectively. N₂O emission happened episodic with highest emissions when heavy rainfall or irrigation coincided with elevated soil mineral N levels and seasonal emissions ranged from 0.80 to 1.07 kg N₂O-N ha^?1 for the different treatments. Emission factors (EF = proportion of N fertilizer emitted as N₂O) over the cotton cropping season, uncorrected for background emissions, ranged from 0.40 to 0.53 % of total N applied for the different treatments. There was no significant effect of the different irrigation treatments on soil N₂O fluxes because highest emission happened in all treatments following heavy rainfall caused by a series of summer thunderstorms which overrode the effect of the irrigation treatment. However, higher irrigation intensity increased the cotton yield and therefore reduced the N₂O intensity (N₂O emission per lint yield) of this cropping system. Our data suggest that there is only limited scope to reduce absolute N₂O emissions by different irrigation intensities in irrigated cotton systems with summer dominated rainfall. However, the significant impact of the irrigation treatments on the N₂O intensity clearly shows that irrigation can easily be used to optimize the N₂O intensity of such a system.