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.     

Emissions of NH3, N2O and CH4 from dairy cows housed in a farmyard manure tying stall (housing, manure storage, manure spreading)

Emission measurements from dairy cows housed in a tying stall were carried out with the aim of finding factors that influence the amount of emissions and means to reduce emissions. All sectors of animal husbandry were investigated. This enabled calculations of emissions for the whole management system including housing, storage and spreading of manure. Emissions during aerobic composting and anaerobic stacking of farmyard manure were compared. NH₃ and N₂O emissions from tying stalls for dairy cows are low (5.8 g NH₃ LU⁻¹ d⁻¹, 619.2 mg N₂O LU⁻¹ d⁻¹). Methane emissions from the animal housing are mainly caused by enteric fermentation. During storage and after spreading of farmyard manure substantial differences concerning NH₃, N₂O and CH₄ emissions were observed with composted and anaerobically stacked farmyard manure. The compost emitted more NH₃ than the anaerobically stacked farmyard manure. About one third of the NH₃ emissions from the anaerobically stacked farmyard manure occurred after spreading. Total N losses were at a low level with both storage systems. Greenhouse gas emissions (N₂O and CH₄) were much higher from the anaerobically stacked farmyard manure than from the composted one. As these are ecologically harmful gases, they have to be considered when judging the form of manure treatment. This revised version was published online in August 2006 with corrections to the Cover Date.     

Nitrate accumulation and greenhouse gas emissions during compost storage

Greenhouse gases (CO₂, CH₄ and N₂O) are emitted during livestock manure handling, including composting, storage and land application. However, published data on emission rates of these gases during storage are sparse. In this study, the levels of GHG emissions and N levels during compost storage were investigated. The compost materials were produced by composting livestock manure for 133 d with 0, 10, 20 and 30% phosphogypsum (PG) or 10, 20 and 30% sand amendment. These compost materials were then stored on a clay pad for 233 d. Results from this study indicated that TN content did not change but mineral N content increased significantly during the 233 d storage for all treatments. The higher mineral N content in compost increases its agronomic value. There were only trace amounts of CH₄ and N₂O emissions. The C loss during storage was mainly as CO₂ and accounted for about 2.9 to 10% of total C initially in the compost. This information is vital to livestock manure life cycle analysis, and can be used to develop best manure management strategies that reduce GHG emissions from livestock production. The LRC Contribution No. 387-06006.     

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.     

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.     

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.     

Greenhouse gas emissions when composting manure from cattle fed wheat dried distillers’ grains with solubles

Dried distillers’ grains with solubles (DDGS) are a co-product of ethanol production that is increasingly available for use as a livestock feed. Including DDGS in diets could affect animal manure properties and impact manure management strategies. The objectives of this study were to investigate changes in the rate of greenhouse gas (GHG) emissions during composting and final properties of manure compost when DDGS is included in feedlot cattle diets. Treatments were: (1) Control; manure from cattle fed a typical finishing diet containing barley (Hordeum vulgare L.) grain and silage and (2) DDGS; manure from cattle fed a finishing diet with 60% DDGS from wheat (Triticum aestivum L.) in the dietary ration. Manure, consisting of feces, urine and wood shavings, was composted in open windrows. Samples were collected for analysis at initiation and completion of composting. Greenhouse gas surface fluxes were collected weekly during the first 4 weeks and every 2–3 weeks for the remainder of the composting period. The DDGS compost had lower total C, but similar total N (TN) content relative to Control, reflecting the initial manure conditions. The DDGS compost also had higher moisture, higher water-extractable NH₄⁺ and NO₃⁻, a greater fraction of TN in available form, and a lower pH than the Control. The O₂ consumption and N₂O emission from DDGS compost were higher, whereas CO₂ and CH₄ emissions were similar to Control. The higher N₂O emissions from DDGS compost were likely related to the high water-extractable N content in DDGS manure. Increased use of DDGS in feedlot diets may have environmental repercussions that include greater emissions of GHG (N₂O) during manure composting. From an end user perspective, enhanced availability of N could increase the nutrient value of the compost for crop production.     

Soil CO<Subscript>2</Subscript>, CH<Subscript>4</Subscript>, and N<Subscript>2</Subscript>O fluxes over and between tile drains on corn,soybean, and forage fields under tile drainage management

Controlled tile drainage (CTD) can benefit the environment and crop production. However, CTD has the potential to increase soil greenhouse gas (GHG: CO₂, CH₄, N₂O) emissions by increasing soil water contents and elevating field water levels. A paired-field (CTD and uncontrolled tile drainage (UTD)) approach was used to compare soil GHG emissions for silt loam corn, soybean, and forage fields under CTD and UTD management in eastern Ontario, Canada during a drier and a wetter growing season. A total of five field pairs were examined. Soil GHG emissions directly over tile drains (OT) and between tile drains (BT) in the CTD fields were also assessed. Average soil GHG emissions did not significantly differ (p > 0.05) for CTD and UTD field pairs, except for CO₂ emissions (greater emissions from UTD fields) among two field pairs studied (forage in the drier growing season and soybean in the wetter growing season), and N₂O emissions from a soybean field pair in the wet growing season (greater emissions from CTD field). Significantly higher soil water contents in the UTD forage field may have augmented CO₂ fluxes there. There were some significantly higher N₂O (in the wetter growing season) and CO₂ emissions (in both growing seasons) BT relative to OT locations in some fields; but these differences were not translated significantly to other BT and OT site comparisons. The wetter growing season examined resulted in greater average daily soil CO₂ fluxes overall, but similar CH₄ and N₂O fluxes for soybean fields compared to soybean fields in the drier growing season. Overall, there were no spatially or temporally systematic differences in GHG emissions among CTD and UTD field pairs, or among BT and OT locations in CTD fields.     

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.     

Greenhouse gas emissions during co-composting of cattle mortalities with manure

Following outbreaks of bovine spongiform encephalopathy (BSE), fewer cattle mortalities are being rendered. Composting may be a viable on-farm alternative for disposal of cattle carcasses. A study was conducted to assess feasibility and greenhouse gas (GHG) emissions during co-composting of cattle mortalities and manure. Using a tractor-mounted front-end loader, windrows were constructed containing manure + straw (control; CK) or manure + straw + cattle mortalities (cattle mortality; CM). The composting process lasted 310 d. The windrows were turned twice, at days 93 and 211, using either a tractor-mounted front-end loader or a specialized shredder bucket. Maximum windrow temperatures were >50 °C for 36 out of 92 d (before first turning) and 142 out of 208 d (after first turning) for the CM treatment and cattle mortalities were completely decomposed except for a few large bones. The cumulative CO₂ and CH₄ emissions were significantly affected by the mortality treatment, but not by the turning technology or their interactions. Significantly higher CO₂ (53.6 g d⁻¹ m⁻²) and CH₄ (2.204 g d⁻¹m⁻²) emissions were observed during the co-composting of cattle mortalities than manure composted with straw (23.0 and 0.742 g d⁻¹m⁻² for CO₂ and CH₄, respectively). Similarly, N₂O emissions were higher with mortalities than without and, for the CM treatment only, higher with shredder bucket than front-end loader turning. In the final compost, CM had higher TN and NH₄⁺-N contents than CK while TC and the C/N ratio were higher with compost turned with the front-end loader than with the shredder bucket. In conclusion, composting was an effective means of disposing of cattle mortalities, but did increase GHG emissions and the N content in the final compost. It is not known if GHG emissions are different than those that would be released from natural decomposition of carcasses. The higher N content in compost containing mortalities would increase its agronomic value.     

Antecedent effect of lime on nitrous oxide and dinitrogen emissions from grassland soils

The antecedent effect of lime on the gaseous products of denitrification (N₂O and N₂) was examined in a laboratory study using a clay loam soil (Soil 1) with a starting pH of 5.4, and a sandy loam soil (Soil 2) with a starting pH of 5.3. The soils were amended with 0, 2.3, 5.7 and 18.9 g CaCO₃ kg^?1, and were incubated for a period of 3 years at 4 °C during which time the soil equilibrated at pH values of 4.7, 5.8, 7.3 and 7.7 (Soil 1) and pH 4.7, 5.2, 6.6 and 7.6 (Soil 2). Ammonium nitrate, labelled with ¹⁵N (¹⁵NH₄NO₃, NH₄ ¹⁵NO₃ and ¹⁵NH₄ ¹⁵NO₃) was added to each incubation jar at a rate of 7.14 μmol N g^?1 oven dried (OD) soil. Headspace gas samples were extracted daily over a 5 days incubation period at 20 °C. The amount of N₂O and N₂, and ¹⁵N enrichment of N₂O-N in the headspace, was determined using continuous-flow isotope-ratio mass spectrometry. As pH increased, the quantity of N₂ and N₂O emitted significantly increased in both soils (P < 0.001), with a peak N₂ flux of 0.179 μmol N g^?1 OD soil h^?1, and a peak N₂O flux of 0.002 μmol N g^?1 OD soil h^?1 occurring at pH 7.6, 2 days after the addition of NH₄NO₃. The loss as N₂ far exceeded the loss of N₂O, which remained at less than 1 % of the total mineral N content of the soil. Lime generally lowered the N₂O:N₂ ratio, however the results from this study suggest that it is not a mitigation strategy for GHG emissions.     

Greenhouse gas emissions as influenced by wetland vegetation degradation along a moisture gradient on the eastern Qinghai-Tibet Plateau of North-West China

Vegetation loss and plant diversity decline in wetlands affect carbon and nitrogen cycling and consequently influence gas fluxes. Although extensive grazing by livestock and climate change have caused significant physical degradation of wetlands on the Qinghai-Tibet Plateau (QTP), and created a clear drainage gradient, the impact on greenhouse gas (GHG) emissions associated with this change has rarely been reported. A 3-year study (2013–2015) was conducted to examine the effect of vegetation change and seasonality on ecosystem respiration, methane (CH₄) and nitrous oxide (N₂O) fluxes in four classes of wetlands with distinct magnitudes of vegetation degradation: healthy vegetation (HV), slightly degraded (SD), moderately degraded, and heavily degraded (HD). We used the dark static chamber-chromatography method to measure the gas fluxes. Highly degraded wetlands were larger C and GHG sources than HV, despite lower methane emissions, due to the loss of gross primary production. SD and HD exhibited the highest cumulative mean annual ecosystem respiration and N₂O emissions, respectively. Ecosystem respiration and CH₄ fluxes were much higher during the growing seasons than in the non-growing seasons. Ecosystem respiration and N₂O fluxes were positively correlated with soil and air temperatures. This points at a potential effect of global warming on GHG emissions from the QTP wetlands. Top soil (0–20 cm) moisture content significantly correlated positively with CH₄ fluxes. Vegetation loss led to a reduced C uptake and increased global warming potential. Therefore, we recommend soil conservation measures and reduced livestock grazing in the wetlands in order to conserve their role as carbon sinks.     

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.     

Dinitrogen and methane gas production during the anaerobic/anoxic decomposition of animal manure

Trace-gas emissions from animal feeding operations (AFOs) can contribute to air quality and global change gases. Previous and current estimated gas emissions from AFOs vary widely and many do not consider all forms of carbon (C) and nitrogen (N) emissions. Studies have found that as methanogenesis in the lagoons increased, conversion of ammonium (NH₄ ⁺) to dinitrogen (N₂) also increased. The purpose of this research was to measure N₂ and CH₄ emissions from swine AFOs in three locations of the U.S. and to evaluate the possible universal relationship between lagoon methanogenesis and the conversion of NH₄ ⁺ to N₂ gas. This relationship was tested by measuring N₂ and CH₄ emissions in two climates at 22 different farms. Methanogenesis was correlated with NH₄ ⁺-to-N₂ conversion by a near-constant N₂ to CH₄ emissions ratio of 0.20, regardless of C loading and climatic effects. The process is shown to be thermodynamically favored when there is competition between NH₄ ⁺ oxidizing reactions. Under methanogenic conditions (redox potentials of methanogenesis) N₂ production is favorable and nitrification/denitrification is not. Thus, N₂ production is stimulated in methanogenic conditions. Evaluation of NH₃ gas emissions from AFOs must consider other N emissions than NH₃. Finally, a statistical model was developed to estimate methane and N₂ emissions (kg gas ha^?1) given feed input per lagoon surface area (kg feed ha^?1) and local air temperature. Further studies are needed to investigate the mechanisms involved in manure processing and isolate the favorable mechanisms into engineering improved manure processing.     

Methane and nitrous oxide emissions from irrigated lowland rice paddies after wheat straw application and midseason aeration

Straw application and midseason drainage play role in controlling methane (CH₄) and nitrous oxide (N₂O) emissions from rice paddy fields, but little information is available on their integrative effect on CH₄ and N₂O emissions. A two-year field experiment was conducted to study the combined effect of timing and duration of midseason aeration and wheat straw incorporation on mitigation of global warming potential (GWP) of CH₄ and N₂O emissions from irrigated lowland rice paddy fields. Results showed that incorporation of wheat straw increased CH₄ by a factor of 5–9 under various water regimes, but simultaneously decreased N₂O emission by 19–42 % during the rice growing season. Without straw incorporation, prolonged aeration significantly reduced the net 100-year GWP of CH₄ and N₂O emissions by 6 %, but also decreased rice production when compared with normal aeration. With straw incorporation, the lowest GWP was found by early aeration, which reduced GWP by 7 and 20 % in 2007 and 2008, respectively. Estimation of net GWPs of CH₄ and N₂O emissions indicated that early midseason drainage with straw incorporation offered the potential to mitigate CH₄ and N₂O emissions from irrigated lowland rice paddies in China.     

Contribution of N2O and NH3 to total greenhouse gas emission from fertilization: results from a sandy soil fertilized with nitrate and biogas digestate with and without nitrification inhibitor

Fertilization with biogas residues from the digestion of energy crops is of growing importance. Digestate from silage maize (Zea mays L.) is a new fertilizer with a high potential for ammonia (NH₃) and nitrous oxide (N₂O) emission. The aim of this study was to determine the effect of different maize fertilization systems [180 kg N ha^?1 in form of calcium nitrate (MIN), biogas digestate from maize (DIG) and biogas digestate from maize mixed with the nitrification inhibitor Piadin (DIG + NI)] on the emission of NH₃ and N₂O from a sandy soil and to assess the total greenhouse gas emission of these fertilization systems. The study is based on a randomized field plot experiment in central Germany and an experimental period of a full year. Annual N₂O-N emission was generally low [0.21 (MIN) to 0.37 (DIG) kg N ha^?1] without differences between treatments. The application of Piadin reduced N₂O emissions by 37 and 62 % during the weeks following digestate application but the annual N₂O emission was not affected by the fertilization treatment. NH₃ emission was only significant for treatments fertilized with digestate. It was not affected by Piadin and accounted for 27 % (+NI) and 29 % of the applied ammonium. Total greenhouse gas emission was dominated by NH₃ losses (reducing the fertilizer value and inducing indirect N₂O emissions) for the treatments fertilized with maize digestate. The most important greenhouse gas emission source of the MIN treatment were emissions from fertilizer production. Our results show the high potential of digestate from maize as a new source of NH₃ emission. Mitigation measures are essential to save the value of this new fertilizer type and to reduce atmospheric and environmental pollution by direct emission of NH₃ and indirect emission of greenhouse gases.     

Greenhouse gas emissions from simulated beef and dairy livestock systems in the United States

Computer spreadsheets were developed to evaluate greenhouse gas (GHG) emissions from U.S. beef and dairy livestock systems from nine locations. Of the beef systems the cow-calf herd emitted the most and feedlot cattle the least methane (CH₄) and nitrous oxide (N₂O) per unit product. Carbon dioxide (CO₂) emissions per unit product were the least for the cow-calf and greatest for the feedlot scenarios. In the dairy systems approximately one-half of the total GHG CO₂ equivalents were from CH₄ and one-third from N₂O. Mitigation strategies, such as intensive grazing, reduced GHG emissions by approximately 10%. This revised version was published online in August 2006 with corrections to the Cover Date.     

Land use legacies and nitrogen fertilization affect methane emissions in the early years of rice field development

Methane (CH₄) emissions are critical to greenhouse gas (GHG) management in agriculture, especially in areas growing rice (Oryza sativa). However, studies on CH₄ emissions and the nitrogen (N) fertilization effect in new rice fields in subtropical regions are still scarce. In this study, we designed a split-plot field experiment in Jiangxi Province, southern China, to examine whether land-use legacies and N fertilization would influence CH₄ emissions. Using static chambers and gas chromatography, we measured CH₄ fluxes in a newly developed rice paddy and a 10-year-old rice paddy. We also measured climatic factors and soil chemical and physical properties to match the flux measurements. The results showed that annual CH₄ emissions in the new rice plots were significantly lower than in the old rice plots regardless of N fertilization. Annual CH₄ emissions increased with the land-use years of rice paddies, following the order of 1 year < 2 years < 3 years < 10 years. N fertilization significantly decreased CH₄ emissions by 36.9% in the first year after the new rice plots were developed, whereas it had no significant effects on CH₄ emissions in the old rice plots or the new rice plots in the second and third years. The results suggest that land-use legacies have significant effects on CH₄ emissions and may influence the N fertilization effect on CH₄ emissions in rice fields in subtropical regions. The findings suggest that land-use legacies should be considered in managing and estimating GHG emissions in rice-growing 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.     

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.