Do cover crops enhance N₂O, CO₂ or CH₄ emissions from soil in Mediterranean arable systems?

Alternatives to maize monocropping in Mediterranean irrigated conditions to reduce greenhouse gas emissions

Winter legume cover crops or double-cropping in high N-fertilizer maize-based sprinkler-irrigated systems enhance agroecosystem diversity and potentially increase yields. However, the effects on direct N2O emissions and global warming potential (GWP) have not been fully established. For two years, in the Ebro Valley (Spain), four maize-based systems consisted of: long-season maize (Zea mays) with winter fallow period (F-LSM) the reference system; or after a leguminous cover crop (common vetch, Vicia sativa) (CC-LSM); and short-season maize after a cereal crop (barley, Hordeum vulgare) (B-SSM) or after a leguminous crop (pea, Pisum sativum) (P-SSM). They were assessed in terms of productivity, direct greenhouse gasses emissions (GHG: N2O, CH4, CO2), and global warming potential (GWP). Direct GHG emissions were measured using the static chamber technique, while soil parameters were monitored. Crop yields and nitrogen uptake were also quantified. GHG emissions linked to management and inputs were calculated to obtain GWP and greenhouse gas intensity (GHGI). The most productive system (B-SSM) obtained the highest direct (79 %, 35 %, and 30 % higher than the F-LSM, P-SSM, and CC-SSM, respectively) and scaled N2O emissions. The P-SSM system had similar N-uptake-scaled emissions to the monocropping (MC) systems. Irrigation, fertilizer, and farm operations accounted for the 26 %, 31 %, and 27 % of the total indirect emissions, respectively. Fertilizer production-related emissions in B-SSM and F-LSM systems were 172 % and 45 % higher than the average emissions in the systems with legumes (461 kg CO2eq. ha-1). Diversified systems lead to slightly higher GHGI values than the reference system (F-LSM). However, no differences were found between the F-LSM and P-SSM systems in GWP (4521 and 5512 kg CO2-eq. ha-1, respectively) or GHGI (144 and 158 kg CO2-eq. ha-1, respectively). The P-SSM system may be a potential alternative for increasing the diversification of maize-based irrigated agrosystems without increasing GHG emissions.

Resilience of aerobic methanotrophs in soils; spotlight on the methane sink under agriculture

Aerobic methanotrophs are a specialized microbial group, catalyzing the oxidation of methane. Disturbance-induced loss of methanotroph diversity/abundance, thus results in the loss of this biological methane sink. Here, we synthesized and conceptualized the resilience of the methanotrophs to sporadic, recurring, and compounded disturbances in soils. The methanotrophs showed remarkable resilience to sporadic disturbances, recovering in activity and population size. However, activity was severely compromised when disturbance persisted or reoccurred at increasing frequency, and was significantly impaired following change in land use. Next, we consolidated the impact of agricultural practices after land conversion on the soil methane sink. The effects of key interventions (tillage, organic matter input, and cover cropping) where much knowledge has been gathered were considered. Pairwise comparisons of these interventions to nontreated agricultural soils indicate that the agriculture-induced impact on the methane sink depends on the cropping system, which can be associated to the physiology of the methanotrophs. The impact of agriculture is more evident in upland soils, where the methanotrophs play a more prominent role than the methanogens in modulating overall methane flux. Although resilient to sporadic disturbances, the methanotrophs are vulnerable to compounded disturbances induced by anthropogenic activities, significantly affecting the methane sink function.

Decarbonization of Agriculture: The Greenhouse Gas Impacts and Economics of Existing and Emerging Climate-Smart Practices

The worldwide emphasis on reducing greenhouse gas (GHG) emissions has increased focus on the potential to mitigate emissions through climate-smart agricultural practices, including regenerative, digital, and controlled environment farming systems. The effectiveness of these solutions largely depends on their ability to address environmental concerns, generate economic returns, and meet supply chain needs. In this Review, we summarize the state of knowledge on the GHG impacts and profitability of these three existing and emerging farming systems. Although we find potential for CO2 mitigation in all three approaches (depending on site-specific and climatic factors), we point to the greater level of research covering the efficacy of regenerative and digital agriculture in tackling non-CO2 emissions (i.e., N2O and CH4), which account for the majority of agriculture's GHG footprint. Despite this greater research coverage, we still find significant methodological and data limitations in accounting for the major GHG fluxes of these practices, especially the lifetime CH4 footprint of more nascent climate-smart regenerative agriculture practices. Across the approaches explored, uncertainties remain about the overall efficacy and persistence of mitigation-particularly with respect to the offsetting of soil carbon sequestration gains by N2O emissions and the lifecycle emissions of controlled environment agriculture systems compared to traditional systems. We find that the economic feasibility of these practices is also system-specific, although regenerative agriculture is generally the most accessible climate-smart approach. Robust incentives (including carbon credit considerations), investments, and policy changes would make these practices more financially accessible to farmers.

Planting and mowing cover crops as livestock feed to synergistically optimize soil properties, economic profit, and environmental burden on pear orchards in the Yangtze River Basin

BACKGROUND

Pears, as an important cash crop, are currently facing great issues due to unsustainable management practices. Cover cropping is a sustainable management strategy that can improve soil fertility and increase fruit yield, while it may also stimulate greenhouse gas emissions. Therefore, synergizing multiple indicators to achieve sustainable development is critical. This study introduces a new management system, namely the planting and mowing of ryegrass as a livestock feed system (PRSS), and analyzes its impact on soil quality, economic benefits, and environmental burdens.

RESULTS

Our results indicated that PRSS could increase soil pH from 5.08 to 5.48 and decrease the content of soil alkali-hydrolyzable nitrogen, total phosphate, and available phosphate (26.96-59.89%) while also enhancing yield (+38.51%) compared with the traditional natural grass management system (TMS). The average soil methane fluxes in PRSS were 72.67 μg m-2  day-1 , higher than those of TMS (61.28 μg m-2  day-1 ). However, the gross primary production was lower than TMS (-37.24%), and no significant difference was observed in soil nitrous oxide fluxes. In different scenarios, the total profit of PRSS mode 1 (mowing ryegrass and selling to a livestock company) and PRSS mode 2 (mowing ryegrass and feeding own sheep) were 10 706.21 $ ha-1 and 26 592.87 $ ha-1 respectively. These values are respectively2.36 times and 5.85 times higher than that of TMS. The total global warming potential of TMS (18.19 t CO2 -eq ha-1 ) was 1.29 t CO2 -eq ha-1 higher and 2.89 t CO2 -eq ha-1 lower than that of PRSS mode 1 and mode 2 respectively.

CONCLUSION

Compared with traditional natural grass, planting and mowing ryegrass in pear orchards can optimize soil properties, increase fruit yield, and reduce global warming potential. Different modes can greatly increase revenue but have varying impacts on environmental burdens. These findings can help rebuild the links between farmland and specialized livestock production, contributing to sustainable development in the pear industries. © 2023 Society of Chemical Industry.

Are service crops an alternative for mitigating N2 O emissions in soybean crops in the Argentinian Pampas?

Service crops (or cover crops) play an important role in simplified agricultural systems. Service crops reduce agricultural external inputs and increase ecosystem services but their ability to mitigate nitrous oxide (N2 O) emissions is still uncertain. The main objective of this study was to evaluate N2 O emissions in soybean-soybean (Glycine max [L.] Merr) rotations that included different service crops. Treatments included continuous soybean with winter fallow and soybean with three service crops: oat (Avena sativa L.), vetch (Vicia villosa Roth.), and a mixture of oat and vetch in a randomized complete block design. Service crops were sown 2 months after soybean harvest and were terminated 2 months before soybean planting. Nitrous oxide emissions were determined during the fourth year of the field experiment. We found that service crops did not significantly affect overall mean N2 O emission rates, with mean emission rates from the fallow, oat, vetch, and oat-vetch treatments of 1.82 ± 0.35, 1.95 ± 0.34, 2.71 ± 0.43, and 2.42 ± 0.42 kg N2 O-N ha-1 per year, respectively. Service crops with low C/N ratios (vetch and oat-vetch mixtures) significantly increased N2 O emissions in spring, after their termination. Overall, soil inorganic N content (NO3 - or NH4 + ) was the main driver that explained the N2 O emissions from different treatments, whereas water-filled pore space controlled the temporal variability of emissions. Our results suggest that service crops with a very short growing season may increase soil N availability for cash crops, but do not reduce N2 O emissions due to long periods of high N availability without crops.

Alfalfa-grass mixtures reduce greenhouse gas emissions and net global warming potential while maintaining yield advantages over monocultures

Improving forage productivity with lower greenhouse gas (GHG) emissions from limited grassland has been a hotspot of interest in global agricultural production. In this study, we analyzed the effects of grasses (tall fescue, smooth bromegrass), legume (alfalfa), and alfalfa-grass (alfalfa + smooth bromegrass and alfalfa + tall fescue) mixtures on GHG emissions, net global warming potential (Net GWP), yield-based greenhouse gas intensity (GHGI), soil chemical properties and forage productivity in cultivated grassland in northwest China during 2020-2021. Our results demonstrated that alfalfa-grass mixtures significantly improved forage productivity. The highest total dry matter yield (DMY) during 2020 and 2021 was obtained from alfalfa-tall fescue (11,311 and 13,338 kg ha^-1) and alfalfa-smooth bromegrass mixtures (10,781 and 12,467 kg ha^-1). The annual cumulative GHG emissions from mixtures were lower than alfalfa monoculture. Alfalfa-grass mixtures significantly reduced GHGI compared with the grass or alfalfa monocultures. Furthermore, results indicated that grass, alfalfa and alfalfa-grass mixtures differentially affected soil chemical properties. Lower soil pH and C/N ratio were recorded in alfalfa monoculture. Alfalfa and mixtures increased soil organic carbon (SOC) and soil total nitrogen (STN) contents. Importantly, alfalfa-grass mixtures are necessary for improving forage productivity and mitigating the GHG emissions in this region. In conclusion, the alfalfa-tall fescue mixture lowered net GWP and GHGI in cultivated grassland while maintaining high forage productivity. These advanced agricultural practices could contribute to the development of climate-sustainable grassland production in China.

Effects of no-tillage on greenhouse gas emissions in maize fields in a semi-humid temperate climate region

Agricultural tillage practices have a significant impact on the generation and consumption of greenhouse gases (GHGs), the primary causes of global warming. Two tillage systems, conventional tillage (CT) and no-tillage (NT), were compared to evaluate their effects on GHG emissions in this study. Averaged from 2018 to 2020, significant decreases of CO₂ and N₂O emissions by 7.4% and 51.1% were observed in NT as compared to those of CT. NT was also found to inhibit the soil CH₄ uptake. In this study, soil was a source of CO₂ and N₂O but a sink for CH₄. The effect of soil temperature on the fluxes of CO₂ was more pronounced than that of soil moisture. However, soil temperature and soil moisture had a weak correlation with CH₄ and N₂O flux variations. As compared to CT, NT did not affect maize yields but significantly reduced global warming potential (GWP) by 8.07%. For yield-scaled GWP, no significant difference was observed in NT (9.63) and CT (10.71). Taken together, NT was an environment-friendly tillage practice to mitigate GHG emissions in the soil under the tested conditions.

Net greenhouse gas balance with cover crops in semi-arid irrigated cropping systems

Climate smart agriculture has been emphasized for mitigating anthropogenic greenhouse gas (GHG) emissions, yet the mitigation potential of individual management practices remain largely unexplored in semi-arid cropping systems. This study evaluated the effects of different winter cover crop mixtures on CO₂ and N₂O emissions, net GHG balance (GHG_net), greenhouse gas intensity (GHGI), yield-scaled GHG emissions, and soil properties in irrigated forage corn (Zea mays L.) and sorghum (Sorghum bicolor L. Moench) rotations. Four cover crop treatments: (1) grasses, brassicas, and legumes mixture (GBL), (2) grasses and brassicas mixture (GB), (3) grasses and legumes mixture (GL), and (4) a no-cover crop (NCC) control, each replicated four times under corn and sorghum phase of the rotations, were tested in the semi-arid Southern Great Plains of USA. Results showed 5–10 times higher soil respiration with cover crop mixtures than NCC during the cover crop phase and no difference during the cash crop phase. The average N₂O-N emission in NCC was 44% lower than GL and 77% lower than GBL in corn and sorghum rotations. Cash crop yield was 13–30% greater in cover crop treatments than NCC, but treatment effects were not observed for GHG_net, yield-scaled emissions, and GHGI. Integrating cover crops could be a climate smart strategy for forage production in irrigated semi-arid agroecosystems.

Regulation of Soil Microbial Community Structure and Biomass to Mitigate Soil Greenhouse Gas Emission

Sustainable reduction of fertilization with technology acquisition for improving soil quality and realizing green food production is a major strategic demand for global agricultural production. Introducing legume (LCCs) and/or non-legume cover crops (NLCCs) during the fallow period before planting main crops such as wheat and corn increases surface coverage, retains soil moisture content, and absorbs excess mineral nutrients, thus reducing pollution. In addition, the cover crops (CCs) supplement the soil nutrients upon decomposition and have a green manure effect. Compared to the traditional bare land, the introduction of CCs systems has multiple ecological benefits, such as improving soil structure, promoting nutrient cycling, improving soil fertility and microbial activity, controlling soil erosion, and inhibiting weed growth, pests, and diseases. The residual decomposition process of cultivated crops after being pressed into the soil will directly change the soil carbon (C) and nitrogen (N) cycle and greenhouse gas emissions (GHGs), and thus affect the soil microbial activities. This key ecological process determines the realization of various ecological and environmental benefits of the cultivated system. Understanding the mechanism of these ecological environmental benefits provides a scientific basis for the restoration and promotion of cultivated crops in dry farming areas of the world. These findings provide an important contribution for understanding the mutual interrelationships and the research in this area, as well as increasing the use of CCs in the soil for better soil fertility, GHGs mitigation, and improving soil microbial community structure. This literature review studies the effects of crop biomass and quality on soil GHGs emissions, microbial biomass, and community structure of the crop cultivation system, aiming to clarify crop cultivation in theory.

Greenhouse gas emissions and C costs of N release associated with cover crop decomposition are plant specific and depend on soil moisture: A microcosm study

Cover cropping is used to improve soil quality and increase N inputs in agricultural systems, but it also may enhance greenhouse gases (GHG) emissions. Here, a 47-d incubation study was conducted to track the decomposition process and evaluate GHG emissions and its drivers and to calculate the C costs of residue-derived N released following the addition of residues from cover crops (pigeon pea, cowpea, lablab bean, vetch, and black oat) and maize under two water-filled pore space (WFPS) levels (40 and 70%). For both WFPS levels, the increase in cumulative CO₂ fluxes in plots that received residues is mainly related with the increment of potentially mineralizable C. Crop residues increased the global warming potential (GWP) under both WFPS levels, with CO₂ emissions accounting for ≥98% of the GWP at 40% WFPS. At 70% WFPS, the GPW increment was driven by a notable increase in N₂ O emissions. The contribution of CH₄ in the GWP emissions was negligible for all the crop residues evaluated. Principal component analysis highlighted that the optimal conditions for production and release are specific for each GHG. The cleaner N source was cowpea at 40% WFPS, which produced only 17.7 kg CO₂ -eq kg^-1 N mineralized, compared with vetch residues, which produced 233 kg CO₂ -eq kg^-1 N mineralized. To integrate agronomic and climate change mitigation perspectives, we suggest considering the C costs of the residue-N released when choosing a cover crop.

Reducing nitrous oxide emissions from irrigated maize by using urea fertilizer in combination with nitrapyrin under different tillage methods

The aim of this study was to evaluate the effectiveness of nitrification inhibitor (nitrapyrin; NI) as a mitigation option for yield-scaled emissions of nitrous oxide (N₂O) under tillage management and urea fertilization in the irrigated maize fields in northern Iran. A split-plot experiment was performed based on a randomized completed blocks design with three replicates. The main plots were the levels of tillage practices (conventional tillage (CT) and minimum tillage (MT), and the subplots were the fertilizer treatments (control, urea, and urea + NI). The gas samples for measuring N₂O emissions were collected during the maize growing season from June to September, using opaque manual circular static chambers. Soil samples were taken at 0-10 cm to determine water-filled pore space, ammonium (NH₄⁺), and nitrate (NO₃^-) concentrations in the soil. When the crop reached physiological maturity, maize was harvested to measure grain yield, biomass production, N uptake of aboveground, and nitrogen use efficiency (NUE). The results showed that the applying NI in combination with urea reduced the total N₂O emissions by up to 58% and 64% in MT and CT, respectively. In the urea + NI treatment, mean soil concentrations of NH₄⁺ and NO₃^- were significantly higher (20%) and lower (23.5%), respectively, compared with other treatments. The NI reduced the yield-scaled N₂O-N emission up to 79% and 55% for CT and MT, respectively. Furthermore, compared to treatment with urea alone, the application of NI increased the NUE of the MT and CT systems by an average of 55% and 46%, respectively. This study emphasized that the application of nitrapyrin should be encouraged in irrigated maize fields, in order to minimize N₂O emissions and improve NUE and biomass production.

Impact of the mixture verses solo residue management and climatic conditions on soil microbial biomass carbon to nitrogen ratio: a systematic review

Cover crops (CCs) have been increasingly cultivated to boost soil quality, crop yield, and minimize environmental degradation compared with no cover crops (NCCs). There is no consensus of CCs under different climatic conditions on soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN), and soil microbial biomass carbon and nitrogen ratio (SMBC/SMBN) are yet documented. Thus, a global meta-analysis of 40 currently available literature was carried out to elucidate the effect of CCs on SMBC and SMBN, and its ratio for cash and cover cropping systems was conducted. Our findings demonstrated that CCs increased SMBC, SMBN, and SMBC/SMBN ratios by 39, 51, and 20%, respectively, as compared to NCCs. The categorical meta-analyzes showed that the mixture of legume and nonlegume CCs decreased the SMBC, SMBN, and SMBC/SMBN ratios relative to the sole legume or nonlegume CCs. Nonlegume CCs enhanced the SMBC, SMBN, and SMBC/SMBN ratio compared to legume CCs. When CCs residues were incorporated into the soil or surface mulched, the SMBC and SMBN increased compared to the removal of residues. The effect of CCs on the SMBN and SMBC/SMBN ratio was higher in medium-textured soils compared to coarser or fine-textured soils, but coarser-textured soils have a higher SMBC. The effect of CCs on SMBN and SMBC/SMBN ratio was prominent on medium-textured soils having soil organic carbon (SOC) in the range of 10-20 mg g^-1, pH > 6.5, and total nitrogen (TN) in the range of 1-2%. It was concluded that CCs enhanced SMBC, SMBN, and its ratio compared to NCCs. The response, however, varied depending on the soil properties and climatic region. Cover crops can boost the biological soil's health by increasing the microbial population's abundance compared to NCCs.

Mitigation of global warming potential and greenhouse gas intensity in arable soil with green manure as source of nitrogen

This study was conducted to determine the effect of different green manure treatments on net GWP and GHGI in upland soil. Barley (B), hairy vetch (HV), and a barley/hairy vetch mixture (BHV) were sown on an upland soil on November 4, 2017 and October 24, 2018. The aboveground biomass of these green manures was incorporated into soil on June 1, 2018 and May 8, 2019. In addition, a fallow treatment (F) was installed as the control. Maize was transplanted as the subsequent crop after incorporation of green manures. Green manuring significantly affected CO₂ and N₂O emission, but not CH₄. Average cumulative soil respiration across years with HV and BHV were 37.0 Mg CO₂ ha^-1 yr^-1 and 35.8 Mg CO₂ ha^-1 yr^-1, respectively and significantly higher than those with under F and B (32.7 Mg CO₂ ha^-1 yr^-1 and 33.0 Mg CO₂ ha^-1 yr^-1, respectively). Cumulative N₂O emissions across years with F and HV were 6.29 kg N₂O ha^-1 yr^-1 and 5.44 kg N₂O ha^-1 yr^-1, respectively and significantly higher than those with B and BHV (4.26 kg N₂O ha^-1 yr^-1 and 4.42 kg N₂O ha^-1 yr^-1, respectively). The net ecosystem carbon budget for HV (-0.5 Mg C ha^-1 yr^-1) was the greatest among the treatments (F; -1.61 Mg C ha^-1 yr^-1, B; -3.98 Mg C ha^-1 yr^-1, and BHV; -0.91 Mg C ha^-1 yr^-1) because of its high biomass yields and the yield of maize after incorporation of HV. There was no significant difference of GHGI among F, HV, and BHV. Incorporation of HV or BHV could reduce net CO₂ emissions per unit of maize grain production as well as F.

Influence of rye cover cropping on denitrification potential and year-round field N2O emissions

Cover cropping is beneficial for reducing soil erosion and nutrient losses, but there are conflicting reports on how cover cropping affects emissions of nitrous oxide (N₂O), a potent greenhouse gas. In this study, we measured N₂O fluxes over a full year in Illinois corn plots with and without rye cover crop. We compared these year-round measurements to N₂O emissions predicted by the Intergovernmental Panel on Climate Change (IPCC) Tier 1 equation and the Denitrification-Decomposition (DNDC) model. In addition, we measured potential denitrification and N₂O production rates. The field measurements showed typical N₂O peaks shortly after fertilizer application, as well as a significant late-winter peak. Cover cropping significantly reduced all peak N₂O fluxes, with decreases ranging from 39 to 95%. Neither model was able to accurately predict annual N₂O fluxes or the decrease in N₂O emissions from cover-cropped fields. In contrast to field measurements, lab assays found that cover cropping significantly increased potential denitrification by 90-127% and potential N₂O production by 54-106%. The rye cover-cropped plots had lower soil nitrate and higher soil carbon. When limiting nitrate and excess carbon were provided in lab assays, the proportion of N₂O resulting from denitrification decreased. These results suggest that the discrepancy between the observed decrease in field N₂O emissions and the increase in denitrification potential may be due to the difference in available nutrients between the field and laboratory measurements. Overall, these results suggest the importance of late-winter peaks in N₂O emissions and the potential of rye cover cropping to reduce N₂O emissions from agricultural fields.

Management of cover crops in temperate climates influences soil organic carbon stocks: a meta-analysis

Increasing the quantity and quality of plant biomass production in space and time can improve the capacity of agroecosystems to capture and store atmospheric carbon (C) in the soil. Cover cropping is a key practice to increase system net primary productivity (NPP) and increase the quantity of high-quality plant residues available for integration into soil organic matter (SOM). Cover crop management and local environmental conditions, however, influence the magnitude of soil C stock change. Here, we used a comprehensive meta-analysis approach to quantify the effect of cover crops on soil C stocks from the 0-30 cm soil depth in temperate climates and to identify key management and ecological factors that impact variation in this response. A total of 40 publications with 181 observations were included in the meta-analysis representing six countries across three different continents. Overall, cover crops had a strong positive effect on soil C stocks (P < 0.0001) leading to a 12% increase, averaging 1.11 Mg C/ha more soil C relative to a no cover crop control. The strongest predictors of SOC response to cover cropping were planting and termination date (i.e., growing window), annual cover crop biomass production, and soil clay content. Cover crops planted as continuous cover or autumn planted and terminated led to 20-30% greater total soil C stocks relative to other cover crop growing windows. Likewise, high annual cover crop biomass production (>7 Mg·ha^-1 ·yr^-1 ) resulted in 30% higher total soil C stocks than lower levels of biomass production. Managing for greater NPP by improving synchronization in cover crop growing windows and climate will enhance the capacity of this practice to drawdown carbon dioxide (CO₂ ) from the atmosphere across agroecosystems. The integration of growing window (potentially as a proxy for biomass growth), climate, and soil factors in decision-support tools are relevant for improving the quantification of soil C stock change under cover crops, particularly with the expansion of terrestrial soil C markets.

N2O Emissions From Residues of Oat and Grass Pea Cover Crops Cultivated in the US Southern Great Plains

Grass pea (Lathyrus sphaericus) and oat (Avena sativa) are potential cover crops for spring periods of summer crop systems in the US Southern Great Plains (SGP). The main objective of this study was to compare nitrous oxide (N2O) emissions from residues of grass pea and oat grown as green nitrogen (N) crops. The comparisons included responses from plots cultivated with oat, grass pea, and control (spring-fallowed) plots. Two management options were applied to grass pea: residues retained and aboveground biomass removed for forage. Crabgrass (Digitaria sanguinalis) was cultivated as a main summer crop immediately after termination of the cover crops. Fluxes of N2O were measured by closed chamber connected to a portable gas analyzer on 23 dates during a 3 month growing period for crabgrass. At termination, oat produced more aboveground biomass than grass pea (2.17 vs. 3.56 Mg ha−1), but total N in biomass was similar (102–104 kg ha−1) due to greater N concentrations in grass pea than oat (4.80% vs. 2.86% of dry mass). Three month cumulative emissions of N2O from grass pea-incorporated plots (0.76 ± 0.11 kg N2O-N ha−1; mean ± standard error, n = 3) were significantly lower than from oat-incorporated plots (1.26 ± 0.14 kg N2O-N ha−1). Emissions from grass pea plots with harvested biomass (0.48 ± 0.04 kg N2O-N ha−1) were significantly lower than those from grass pea-incorporated plots. Cumulative N2O emissions from control plots were significantly greater than those from grass pea-harvested plots but were similar to the emissions from grass pea-incorporated plots. Yields produced by crabgrass were similar from all cover crop treatments (8.65–10.46 Mg ha−1), but yield responses to the control (18.53 Mg ha−1) were significantly larger. Nitrogen concentrations in crabgrass were greater in response to oat- and grass pea-incorporated plots (2.86–2.87%) than in grass pea-harvested (1.93%) and control (1.44%) plots. In conclusion, the results indicated that (i) post-incorporation emissions of N2O can be greater from a non-legume green N crop than a legume green N crop due to greater biomass productivity of the cereal, and (ii) emissions of N2O could be mitigated by removing biomass of the green N crop for use as forage.

The effect of chemical and organic N inputs on N2O emission from rain-fed crops in Eastern Mediterranean

Nitrogen has a significant contribution to global warming and its reduction in agriculture is expected to reduce N₂O emissions having however adverse effects on the productivity of agricultural ecosystems. Maintaining systems productivity with alternative N sources i.e manure and composts could be a strategy also to mitigate N₂O emissions. In this paper, we present the effect of different N sources (organic and chemical) on field N₂O emissions and how these emissions are associated with soil available N forms (NH₄⁺ and NO₃^-) in three different rain-fed crops namely barley, pea and vetch grown in Cyprus for two growing seasons. The daily emissions ranged from -3.11 to 12.3 g N-N₂O/ha/day, while cumulative emissions ranged from 119 g N-N₂O/ha to 660 g N-N₂O/ha depending on crop and nitrogen source type. The emissions showed a seasonal pattern and WFPS has been identified as a critical soil parameter controlling daily N₂O emissions. The daily N₂O fluxes in the current study derives mainly from nitrification irrespectively crop type or nitrogen source type. Specific emission factors for each crop cultivated under different N source type were calculated and ranged from 0.03% ± 0.02-0.34% ± 0.09. The application of manure and chemical fertilizers cause similar intensity of N₂O emissions while compost exhibited the lower emission factors. These findings suggest that composts could be integrated in a nutrient management strategy of rain-fed crops with less N₂O emissions. The high background emissions found suggest also that other factors than external inputs are associated with N₂O emissions and further studies including the response of microbial community structure and their contribution and association with N₂O emissions.

Ridge-furrow mulching system and supplementary irrigation can reduce the greenhouse gas emission intensity

In this study, in order to explore the greenhouse gas emissions and global warming potential (GWP) in winter wheat fields under the ridge-furrow mulching system (RF) with supplementary irrigation, three rainfall conditions (heavy rainfall = 275 mm, normal rainfall = 200 mm, and light rainfall = 125 mm) and four irrigation treatments (150, 75, 37.5, and 0 mm) were simulated during the growth period. Traditional flat planting (TF) was used as the control and we determined the emissions of N₂O, CO₂, and CH₄, as well as the GWP and greenhouse gas emission intensity (GHGI). The results obtained after three years (October 2016 to June 2019) showed that when the amount of irrigation was the same during the winter wheat growth period, the N₂O emission flux, CO₂ emission flux, and GHGI under RF decreased by 3.30-23.78%, 5.93-6.45%, and 5.01-23.72% with rainfall at 275 mm, respectively, compared with those under TF. Under the same level of supplementary irrigation, the N₂O emission flux, CO₂ emission flux, and GHGI decreased by 0.8-4.18%, 5.05-13.53%, and 7.83-13.72%, respectively, with rainfall at 200 mm, and they decreased by 17.49-32.46%, 25.57-35.35%, and 6.22-30.20% with rainfall at 125 mm. Under the three rainfall conditions, the absorption of CH4 in the winter wheat field increased as the supplementary irrigation decreased. Our results showed that the RF system can satisfy the goal of achieving high yields and saving water, as well as reducing the GHGI to contribute less to global climate warming as an environmentally friendly irrigation method.

Short-term grazing of cover crops and maize residue impacts on soil greenhouse gas fluxes in two Mollisols

An integrated crop-livestock system (ICLS), when managed properly, can help in mitigating soil surface greenhouse gas (GHG) fluxes, especially carbon dioxide (CO₂ ), methane (CH₄ ), and nitrous oxide (N₂ O). However, the impacts of an ICLS on GHG fluxes are poorly understood. The present study was conducted at two sites (northern Brookings [Brookings-N] and northwestern Brookings [Brookings-NW]) established in 2016 and 2017, respectively, under loamy soils in South Dakota. The specific objective was to evaluate the impact of cover crops (CCs) and grazed CCs under oat (Avena sativa L.)-CCs-maize (Zea mays L.) rotation on GHG fluxes. Study treatments included the following: (a) a legume-dominated CC (LdC), (b) a cattle-grazed LdC (LdC+G), (c) a grass-dominated CC (GdC), (d) a cattle-grazed GdC (GdC+G), and (e) one without CC or grazing (NC). Greenhouse gas monitoring occurred weekly during the growing crop seasons in 2016 and 2017 for Brookings-N and in 2017 and 2018 for Brookings-NW. Data showed that cumulative CO₂ and N₂ O fluxes at Brookings-N were lower for GdC+G (4042 kg C ha^-1 for CO₂ and 1499 g N ha^-1 for N₂ O) than for LdC+G (4819 kg C ha^-1 for CO₂ and 2017 g N ha^-1 for N₂ O), indicating the superiority of GdC+G over LdC+G in reducing GHG fluxes. However, no effect from grazed CC on cumulative CO₂ and N₂ O fluxes were observed at the Brookings-NW site. Cumulative CH₄ flux was not affected by an ICLS at either site. This short-term investigation showed that, in general, CCs and grazing of CCs and maize residue did not impact GHG fluxes.

Cover Crop Impact on Soil Organic Carbon, Nitrogen Dynamics and Microbial Diversity in a Mediterranean Semiarid Vineyard

Cover crop (CC) management in vineyards increases sustainability by improving soil chemical and biological fertility, but knowledge on its effects in semiarid soils is lacking. This study evaluated the effect of leguminous CC management on soil organic carbon (SOC) sequestration, soil nitrate content and microbial diversity in a semiarid vineyard, in comparison to conventional tillage (CT). SOC and nitrate were monitored during vine-growing season; soil respiration, determined by incubation experiments, microbial biomass and diversity was analyzed after CC burial. The microbial diversity was evaluated by bacterial and fungal automated ribosomal intergenic spacer analysis (ARISA) and high-throughput sequencing of 16SrDNA. CC increased nitrate content and, although it had no relevant effect on SOC, almost doubled its active microbial component, which contributes to SOC stabilization. An unexpected stability of the microbial communities under different soil managements was assessed, fungal diversity being slightly enhanced under CT while bacterial diversity increased under CC. The complete nitrifying genus Nitrospira and plant growth-promoting genera were increased under CC, while desiccation-tolerant genera were abundant in CT. Findings showed that temporary CC applied in semiarid vineyards does not optimize the provided ecosystem services, hence a proper management protocol for dry environments should be set up.

Effect of low C/N crop residue input on N2O, NO, and CH4 fluxes from Andosol and Fluvisol fields

Crop residues are produced from agriculture in large amounts globally. Crop residues are known to be a source of nitrous oxide (N₂O); however, contrasting results have been reported. Furthermore, the effect of crop residues on nitric oxide (NO) and methane (CH₄) fluxes has not been well studied. We investigated N₂O, NO, and CH₄ fluxes after low C/N crop residue (cabbages and potatoes) inputs to lysimeter fields for two years using with automated flux monitoring system. Lysimeters were filled with two contrasting soil types, Andosol (total C: 33.1 g kg^-1; clay: 18%) and Fluvisol (17.7 g kg^-1; 36%). Nitrogen application rates were 250 kg N ha^-1 of synthetic fertilizer and 272 kg N ha^-1 of cow manure compost for cabbage, and 120 kg N ha^-1 of synthetic fertilizer and 136 kg N ha^-1 of cow manure compost for potato, respectively. Large N₂O peaks were observed after crop residues were left on the surface of the soil for 1 to 2 weeks in summer, but not in winter. The annual N₂O emission factors (EFs) for cabbage residues were 3.02% and 5.37% for Andosol and Fluvisol, respectively. Those for potatoes were 7.51% and 5.10% for Andosol and Fluvisol, respectively. The EFs were much higher than the mean EFs of synthetic fertilizers from Japan's agricultural fields (0.62%). Moreover, the EFs were much higher than the Intergovernmental Panel on Climate Change (IPCC) default N₂O EFs for synthetic fertilizers and crop residues (1%). The annual NO EFs for potatoes were 1.35% and 2.44% for Andosol and Fluvisol, respectively, while no emission was observed after cabbage residue input. Crop residues did not affect CH₄ uptake by soil. Our results suggest that low C/N crop residue input to soils can create a hotspot of N₂O emission, when temperature and water conditions are not limiting factors for microbial activity.

Integrated management for sustainable cropping systems: Looking beyond the greenhouse balance at the field scale

Cover crops (CC) promote the accumulation of soil organic carbon (SOC), which provides multiple benefits to agro-ecosystems. However, additional nitrogen (N) inputs into the soil could offset the CO2 mitigation potential due to increasing N2 O emissions. Integrated management approaches use organic and synthetic fertilizers to maximize yields while minimizing impacts by crop sequencing adapted to local conditions. The goal of this work was to test whether integrated management, centered on CC adoption, has the potential to maximize SOC stocks without increasing the soil greenhouse gas (GHG) net flux and other agro-environmental impacts such as nitrate leaching. To this purpose, we ran the DayCent bio-geochemistry model on 8,554 soil sampling locations across the European Union. We found that soil N2 O emissions could be limited with simple crop sequencing rules, such as switching from leguminous to grass CC when the GHG flux was positive (source). Additional reductions of synthetic fertilizers applications are possible through better accounting for N available in green manures and from mineralization of soil reservoirs while maintaining cash crop yields. Therefore, our results suggest that a CC integrated management approach can maximize the agro-environmental performance of cropping systems while reducing environmental trade-offs.

Greenhouse Gas Emissions from Soil Cultivated with Vegetables in Crop Rotation under Integrated, Organic and Organic Conservation Management in a Mediterranean Environment

A combination of organic and conservation approaches have not been widely tested, neither considering agronomic implications nor the impacts on the environment. Focussing on the effect of agricultural practices on greenhouse gas (GHG) emissions from soil, the hypothesis of this research is that the organic conservation system (ORG+) may reduce emissions of N2O, CH4 and CO2 from soil, compared to an integrated farming system (INT) and an organic (ORG) system in a two-year irrigated vegetable crop rotation set up in 2014, in a Mediterranean environment. The crop rotation included: Savoy cabbage (Brassica oleracea var. sabauda L. cv. Famosa), spring lettuce (Lactuca sativa L. cv. Justine), fennel (Foeniculum vulgare Mill. cv. Montebianco) and summer lettuce (L. sativa cv. Ballerina). Fluxes from soil of N2O, CH4 and CO2 were measured from October 2014 to July 2016 with the flow-through non-steady state chamber technique using a mobile instrument equipped with high precision analysers. Both cumulative and daily N2O emissions were mainly lower in ORG+ than in INT and ORG. All the cropping systems acted as a sink of CH4, with no significant differences among treatments. The ORG and ORG+ systems accounted for higher cumulative and daily CO2 emissions than INT, maybe due to the stimulating effect on soil respiration of organic material (fertilizers/plant biomass) supplied in ORG and ORG+. Overall, the integration of conservation and organic agriculture showed a tendency for higher CO2 emissions and lower N2O emissions than the other treatments, without any clear results on its potential for mitigating GHG emissions from soil.

The effects of different soil nutrient management schemes in nitrogen cycling

It is imperative for sustainable agriculture to explore practices and inputs creating low N₂O emission capacity without reducing the productivity of the agricultural system. To evaluate different nutrient management schemes, a microcosm study was conducted to assess the direct N₂O emission from soil. Four different treatments were used to provide a preliminary assessment of N₂O emissions, as well as the concentrations of nitrates (NO₃^-) and ammonium (NH₄⁺) produced in soil: compost (derived from green plant residues), chickpea residues (green manure) in two different N concentrations (2.6% and 5.5%, respectively) and ammonium nitrate (fertilizer). The soil was thoroughly mixed with the organic amendments and ammonium nitrate and incubated for 31 days. The emissions of N₂O were higher in green manure with high-N content, as a source of nitrogen in the soil, and were similar to the emissions measured from the chemically fertilized soil. In particular, chickpea residues, with high-N content, exhibited cumulative N₂O emissions, equal to 266.17 μg N/m², whereas in fertilized soil the emissions were 267.10 μg N/m². On the contrary, the incorporation of chickpea plant residues with low-N content can be an efficient way to minimize the N₂O emissions at 21.63 μg N/m². The emissions of N₂O when compost was applied, remained relatively low, equal to 5.47 μg N/m², and in comparison to soil without any treatment. Overall, a positive association between NH₄⁺, NO₃^- in soil and N₂O emissions were observed. However, this response was treatment depended, and the significant positive correlation between NH₄⁺ and N₂O emissions were noticed in soils treated with ammonium nitrate, chickpea residues with low N content, as well as untreated controls. On the contrary, the positive correlation observed between NO₃^- and N₂O emissions in soils receiving compost and high N chickpea residues, suggest that the different treatments are differentially affecting the processes that are contributing to N₂O emissions in agricultural soils. These findings, emphasize that the different nutrient management schemes are differentially affecting the main process contributing to N₂O emissions in agricultural soils.

Benefits of sustainable management practices on mitigating greenhouse gas emissions in soybean crop (Glycine max)

Soybean in Iran is managed intensively and represents an important source of greenhouse gas (GHG). Developing an agronomic management that reduces GHG emissions while still ensuring optimum soybean yields is strongly required. Field experiments were conducted in 2014 and 2015 growing seasons in the Golestan province (North of Iran) to evaluate different combinations of GHG mitigation strategies for soybean cultivation. Treatments included: two tillage methods [conventional tillage (CT) and no-tillage (ZT)], two residue management [wheat residue removed (R-) and wheat residue left on the system (R+)] and four levels of nitrogen (N) fertilization [0, 40, 80 and 120 kg N ha-1 (N1, N2, N3 and N4, respectively)]. Soil moisture and temperature, GHG fluxes, yield and agronomic efficiency of nitrogen (AEN) were measured. The CT and R+ generally caused greater CO2 fluxes than the ZT and R-, respectively. The maximum CO2 flux occurred in August and this was about 362.6 and 284 mg m-2 h-1 under CT-R + -N4 and ZT-R + -N4. Soil CO2 emissions were higher in fertilized than non-fertilized treatments. Wheat residue left on the system under ZT reduced N2O emissions than CT, especially in N1. The cumulative N2O emissions were maximum under CT-R + -N4 and minimum under ZTR + -N1 (2.28 and 0.70 kg N2O-N ha-1, respectively). In this study, there was no significant effect on CH4 emissions. Soybean yield was similar among tillage systems and residue management, while N3 in combination with wheat residue showed the highest response of seed yield. CO2 emissions per unit of grain yield were the lowest under no-tillage associated with wheat residue mulch and nitrogen fertilizer. The results showed that GHG emissions could be mitigated in soybean crop in Iran. In particular, wheat residues left on the soil surface under no-tillage with 80 kg N ha-1 showed a reduction of GHG emissions, maintain crop yield providing environmentally-friendly option.

Mitigating greenhouse gas emissions in subsurface-drained field using RZWQM2

Greenhouse gas (GHG) emissions from agricultural soils are affected by various environmental factors and agronomic practices. The impact of inorganic nitrogen (N) fertilization rates and timing, and water table management practices on N₂O and CO₂ emissions were investigated to propose mitigation and adaptation efforts based on simulated results founded on field data. Drawing on 2012-2015 data measured on a subsurface-drained corn (Zea mays L.) field in Southern Quebec, the Root Zone Water Quality Model 2 (RZWQM2) was calibrated and validated for the estimation of N₂O and CO₂ emissions under free drainage (FD) and controlled drainage with sub-irrigation (CD-SI). Long term simulation from 1971 to 2000 suggested that the optimal N fertilization should be in the range of 125 to 175 kg N ha^-1 to obtain higher NUE (nitrogen use efficiency, 7-14%) and lower N₂O emission (8-22%), compared to 200 kg N ha^-1 for corn-soybean rotation (CS). While remaining crop yields, splitting N application would potentially decrease total N₂O emissions by 11.0%. Due to higher soil moisture and lower soil O₂ under CD-SI, CO₂ emissions declined by 6% while N₂O emissions increased by 21% compared to FD. The CS system reduced CO₂ and N₂O emissions by 18.8% and 20.7%, respectively, when compared with continuous corn production. This study concludes that RZWQM2 model is capable of predicting GHG emissions, and GHG emissions from agriculture can be mitigated using agronomic management.

Impacts of Early- and Late-Terminated Cover Crops on Gas Fluxes

Cover crops (CCs) could alter soil processes, but the effects of early versus late termination of CCs on gas fluxes are not well known. We evaluated temporal changes in fluxes of CO, NO, and CH and related soil properties in no-till corn ( L.) with and without winter rye ( L.) CCs that were terminated early (30 d before planting) or late (at planting) in a rainfed silty clay loam and an irrigated silt loam in Nebraska from April 2016 to June 2017. Gas fluxes, soil temperature, and soil water content were measured biweekly to monthly, and wet aggregate stability and particulate organic matter concentrations were measured seasonally. We also compared our results with a global literature review. Late-terminated CCs did not affect CH fluxes but increased daily CO fluxes by 59% compared with no CC at both sites and NO fluxes by 92% at the rainfed site only. Early termination did not affect gas fluxes. Termination date did not affect cumulative fluxes and had minimal effects on soil properties. The literature review supports our study results, which indicate that CC effects on (i) CO fluxes are driven by plant respiration during the CC growing period, and (ii) NO and CH fluxes are minimal under grass CCs. Overall, under no-till, CC termination date has small effects on NO and CH fluxes, but late CC termination can increase CO fluxes in spring due to greater biomass yield compared with early termination.

Long-term no-tillage application increases soil organic carbon, nitrous oxide emissions and faba bean (Vicia faba L.) yields under rain-fed Mediterranean conditions

The introduction of legumes into crop sequences and the reduction of tillage intensity are both proposed as agronomic practices to mitigate the soil degradation and negative impact of agriculture on the environment. However, the joint effects of these practices on nitrous oxide (N₂O) and ammonia (NH₃) emissions from soil remain unclear, particularly concerning semiarid Mediterranean areas. In the frame of a long-term field experiment (23 years), a 2-year study was performed on the faba bean (Vicia faba L.) to evaluate the effects of the long-term use of no tillage (NT) compared to conventional tillage (CT) on yield and N₂O and NH₃ emissions from a Vertisol in a semiarid Mediterranean environment. Changes induced by the tillage system in soil bulk density, water filled pore space (WFPS), organic carbon (TOC) and total nitrogen (TN), denitrifying enzyme activity (DEA), and bacterial gene (16S, amoA, and nosZ) abundance were measured as parameters potentially affecting N gas emissions. No tillage, compared with CT, significantly increased the faba bean grain yield by 23%. The tillage system had no significant effect on soil NH₃ emissions. Total N₂O emissions, averaged over two cropping seasons, were higher in NT than those in CT plots (2.58 vs 1.71 kg N₂O-N ha^-1, respectively; P < 0.01). In addition, DEA was higher in NT compared to that in CT (74.6 vs 18.6 μg N₂O-N kg^-1 h^-1; P < 0.01). The higher N₂O emissions in NT plots were ascribed to the increase of soil bulk density and WFPS, bacteria (16S abundance was 96% higher in NT than that in CT) and N cycle genes (amoA and nosZ abundances were respectively 154% and 84% higher in NT than that in CT). The total N₂O emissions in faba bean were similar to those measured in other N-fertilized crops. In conclusion, a full evaluation of NT technique, besides the benefits on soil characteristics (e.g. TOC increase) and crop yield, must take into account some criticisms related to the increase of N₂O emissions compared to CT.

The effect of nitrification inhibitors on NH3 and N2O emissions in highly N fertilized irrigated Mediterranean cropping systems

There is an increasing concern about the negative impacts associated to the release of reactive nitrogen (N) from highly fertilized agro-ecosystems. Ammonia (NH₃) and nitrous oxide (N₂O) are harmful N pollutants that may contribute both directly and indirectly to global warming. Surface applied manure, urea and ammonium (NH₄⁺) based fertilizers are important anthropogenic sources of these emissions. Nitrification inhibitors (NIs) have been proposed as a useful technological approach to reduce N₂O emission although they can lead to large NH₃ losses due to increasing NH₄⁺ pool in soils. In this context, a field experiment was carried out in a maize field with aiming to simultaneously quantify NH₃ volatilization and N₂O emission, assessing the effect of two NIs 3,4‑dimethilpyrazol phosphate (DMPP) and 3,4‑dimethylpyrazole succinic acid (DMPSA). The first treatment was pig slurry (PS) before seeding (50 kg N ha^-1) and calcium ammonium nitrate (CAN) at top-dressing (150 kg N ha^-1), and the second was DMPP diluted in PS (PS + DMPP) (50 kg N ha^-1) and CAN + DMPSA (150 kg N ha^-1) also before seeding and at top-dressing, respectively. Ammonia emissions were quantified by a micrometeorological method during 20 days after fertilization and N₂O emissions were assessed using manual static chambers during all crop period. The treatment with NIs was effective in reducing c. 30% cumulative N₂O losses. However, considering only direct N₂O emissions after second fertilization event, a significant reduction was not observed using CAN+DMPSA, probably because high WFPS of soil, driven by irrigation, favored denitrification. Cumulative NH₃ losses were not significantly affected by NIs. Indeed, NH₃ volatilization accounted 14% and 10% of N applied in PS + DMPP and PS plots, respectively and c. 2% of total N applied in CAN+DMPSA and CAN plots. Since important NH₃ losses still exist even although abating strategies are implemented, structural and political initiatives are needed to face this issue.

Response of Soil Surface Greenhouse Gas Fluxes to Crop Residue Removal and Cover Crops under a Corn-Soybean Rotation

Excessive crop residue returned to the soil hinders farm operations, but residue removal can affect soil quality. In contrast, cover cropping can return additional residue to the soil and improve soils and environmental quality compared with no cover cropping. Residue and cover crop impacts on soil surface greenhouses gas (GHG) emissions are undetermined and site specific. Thus, the present study was conducted to investigate the impacts of corn ( L.) residue management and cover cropping on GHG fluxes. The fluxes were measured from 2013 to 2015 using static chamber under corn and soybean [ (L.) Merr.] rotation initiated in 2000 at Brookings, SD. Treatments included two residue management levels (residue returned [RR] and residue not returned [RNR]) and two cover cropping (cover crops [CC] and no cover crops [NCC]). Results showed that RR under corn and soybean phases significantly reduced cumulative CO fluxes (2681.3 kg ha in corn and 2419.8 kg ha in soybeans) compared with RNR (3331.0 kg ha in corn and 2755.0 kg ha in soybeans) in 2013. The RR emitted significantly less cumulative NO fluxes than RNR from both the phases in 2013 and 2014, but not in 2015. The CC treatment had significantly lower cumulative NO fluxes than the NCC for corn and soybean phases in 2013 and 2014. We conclude that crop residue retention and cover cropping can mitigate the GHG emissions compared with residue removal and no cover cropping.

Potential role of compost and green manure amendment to mitigate soil GHGs emissions in Mediterranean drip irrigated maize production systems

Organic fertilization can preserve soil organic matter (SOM) and is foreseen as an effective strategy to reduce green house gases (GHGs) emissions in agriculture. However, its effectiveness needs to be clarified under specific climate, crop management and soil characteristics. A field experiment was carried out in a Mediterranean drip irrigated maize system to assess the pattern of soil CO₂ and N₂O fluxes in response to the replacement of a typical bare fallow-maize cycle under urea fertilization (130 kg N ha^-1 y^-1) (CONV) with: (i) bare fallow-maize cycles under two doses of compost (COM1 and COM2, 130 and 260 kg N ha^-1 y^-1, respectively) and (ii) a vetch-maize cycle, with vetch incorporation as green manure (130 kg N ha^-1 y^-1) (GMAN). Along the maize period (MP), reduced daily N₂O emissions were detected in organic treated soils compared to CONV, mainly in the first stages of the cultivation, thanks to the slow release of available nitrogen from the organic substrates. Cumulative N₂O fluxes (kg N₂O-N ha^-1) in MP scored to 0.24, 0.14, 0.12 and 0.085 for CONV, COM1, COM2 and GMAN, respectively, with significantly lower emissions in GMAN respect to CONV. CO₂ fluxes partially reflected the ranking observed for maize yields, with cumulated values (Mg CO₂-C ha^-1) of 2.2, 1.5, 2.1, 2.1 for CONV, COM1, COM2 and GMAN, respectively, and significantly lower in COM1 respect to the other treatments. During the fallow period (FP), compared to CONV (0.77 Mg CO₂-C ha^-1 and 0.25 kg N₂O-N ha^-1), enhanced GHG fluxes were detected in COM treatments (about 0.90 Mg CO₂-C ha^-1 and 0.37 kg N₂O-N ha^-1, as averaged values from COM1 and COM2), likely driven by the slow prolonged mineralization of the added organic matter. GMAN showed comparable CO₂ (0.82 Mg CO₂-C ha^-1) and N₂O emissions (0.30 kg N₂O-N ha^-1), in consequence of restrained post-harvest residual N coupled with the counteracting effect of vetch uptake. Respect to the total yearly GHG emissions in CONV (about 194 kg CO₂ eq ha^-1 y^-1), the overall results showed commensurate slightly higher GWP in COM treatments (+11% as averaged value from COM1 and COM2). The yield-scaled global warming potential (GWP) resulted 60% higher and nearly doubled for COM2 and COM1 respectively, according to the lower COM yields, markedly dampening at halved compost dose. GMAN appeared the best performing organic treatment, with lower GWP (-27%) and competitive yields respect to CONV. All treatments showed N₂O emission factors consistently lower compared with the default IPCC 1% value.

Chinese Milk Vetch as Green Manure Mitigates Nitrous Oxide Emission from Monocropped Rice System in South China

Monocropped rice system is an important intensive cropping system for food security in China. Green manure (GM) as an alternative to fertilizer N (FN) is useful for improving soil quality. However, few studies have examined the effect of Chinese milk vetch (CMV) as GM on nitrous oxide (N₂O) emission from monocropped rice field in south China. Therefore, a pot-culture experiment with four treatments (control, no FN and CMV; CMV as GM alone, M; fertilizer N alone, FN; integrating fertilizer N with CMV, NM) was performed to investigate the effect of incorporating CMV as GM on N₂O emission using a closed chamber-gas chromatography (GC) technique during the rice growing periods. Under the same N rate, incorporating CMV as GM (the treatments of M and NM) mitigated N₂O emission during the growing periods of rice plant, reduced the NO₃^- content and activities of nitrate and nitrite reductase as well as the population of nitrifying bacteria in top soil at maturity stage of rice plant versus FN pots. The global warming potential (GWP) and greenhouse gas intensity (GHGI) of N₂O from monocropped rice field was ranked as M<NM<FN. However, the treatment of NM increased rice grain yield and soil NH₄⁺ content, which were dramatically decreased in the M pots, over the treatment of FN. Hence, it can be concluded that integrating FN with CMV as GM is a feasible tactic for food security and N₂O mitigation in the monocropped rice based system.

Management of agricultural soils for greenhouse gas mitigation: Learning from a case study in NE Spain

A portfolio of agricultural practices is now available that can contribute to reaching European mitigation targets. Among them, the management of agricultural soils has a large potential for reducing GHG emissions or sequestering carbon. Many of the practices are based on well tested agronomic and technical know-how, with proven benefits for farmers and the environment. A suite of practices has to be used since none of the practices can provide a unique solution. However, there are limitations in the process of policy development: (a) agricultural activities are based on biological processes and thus, these practices are location specific and climate, soils and crops determine their agronomic potential; (b) since agriculture sustains rural communities, the costs and potential for implementation have also to be regionally evaluated and (c) the aggregated regional potential of the combination of practices has to be defined in order to inform abatement targets. We believe that, when implementing mitigation practices, three questions are important: Are they cost-effective for farmers? Do they reduce GHG emissions? What policies favour their implementation? This study addressed these questions in three sequential steps. First, mapping the use of representative soil management practices in the European regions to provide a spatial context to upscale the local results. Second, using a Marginal Abatement Cost Curve (MACC) in a Mediterranean case study (NE Spain) for ranking soil management practices in terms of their cost-effectiveness. Finally, using a wedge approach of the practices as a complementary tool to link science to mitigation policy. A set of soil management practices was found to be financially attractive for Mediterranean farmers, which in turn could achieve significant abatements (e.g., 1.34 MtCO2e in the case study region). The quantitative analysis was completed by a discussion of potential farming and policy choices to shape realistic mitigation policy at European regional level.

Characteristics of N2O production and transport within soil profiles subjected to different nitrogen application rates in China

To better understand the effect of N fertilizer on the responses of subsoil N2O to N2O emissions in a high-yield plot, we investigated the subsurface N2O concentrations at seven mineral soil depths and analyzed the subsoil N2O fluxes between soil horizons. This study was conducted from 2012 to 2013 in farmland located in the semi-humid area of the Changwu station, Shaanxi, and the results showed that the application of N fertilizer triggered the highest amount of N2O production and effluxes in the various soil layers. With an increase of N fertilizer, N2O effluxes and production significantly increased; the mean variation of 380 kg N ha(-1) treatment was much greater than that of 250 kg N ha(-1) treatment, particularly after fertilization during the maize growing season (MS). N2O concentrations increased within 30 cm and maintained low and stable values. However, N2O fluxes and production decreased with depth (below 30 cm) and then remained low (approximately zero or even negative) at depths of 30-90 cm. The cumulative N2O fluxes in the 0-15 cm soil layer accounted for 99.0% of the total amount in the soil profile, and high fluxes coincided with periods of relatively high production rates. The cumulative production of N2O also remained in step with the cumulative fluxes. In addition, more N fertilizer was applied, greater production occurred in the topsoil. A significantly positive relationship was found between N2O fluxes and mineral N, and a negative relationship was found between the fluxes and the water-filled pore space (WFPS) in the shallow soil. N2O effluxes increased with increasing amounts of N fertilizer, which was primarily due to nitrification on the Loess Plateau.

N2O and CH4 emissions from a fallow-wheat rotation with low N input in conservation and conventional tillage under a Mediterranean agroecosystem

Conservation agriculture that includes no tillage (NT) or minimum tillage (MT) and crop rotation is an effective practice to increase soil organic matter in Mediterranean semiarid agrosystems. But the impact of these agricultural practices on greenhouse gases (GHGs), such as nitrous oxide (N2O) and methane (CH4), is variable depending mainly on soil structure and short/long-term tillage. The main objective of this study was to assess the long-term effect of three tillage systems (NT, MT and conventional tillage (CT)) and land-covers (fallow/wheat) on the emissions of N2O and CH4 in a low N input agricultural system during one year. This was achieved by measuring crop yields, soil mineral N and dissolved organic C contents, and fluxes of N2O and CH4. Total cumulative N2O emissions were not significantly different (P>0.05) among the tillage systems or between fallow and wheat. The only difference was produced in spring, when N2O emissions were significantly higher (P<0.05) in fallow than in wheat subplots, and NT reduced N2O emissions (P<0.05) compared with MT and CT. Taking into account the water filled pore space (WFPS), both nitrification and denitrification could have occurred during the experimental period. Denitrification capacity in March was similar in all tillage systems, in spite of the higher DOC content maintained in the topsoil of NT. This could be due to the similar denitrifier densities, targeted by nirK copy numbers at that time. Cumulative CH4 fluxes resulted in small net uptake for all treatments, and no significant differences were found among tillage systems or between fallow and wheat land-covers. These results suggest that under a coarse-textured soil in low N agricultural systems, the impact of tillage on GHG is very low and that the fallow cycle within a crop rotation is not a useful strategy to reduce GHG emissions.

Methane, carbon dioxide and nitrous oxide fluxes in soil profile under a winter wheat-summer maize rotation in the North China Plain

The production and consumption of the greenhouse gases (GHGs) methane (CH4), carbon dioxide (CO2) and nitrous oxide (N2O) in soil profile are poorly understood. This work sought to quantify the GHG production and consumption at seven depths (0-30, 30-60, 60-90, 90-150, 150-200, 200-250 and 250-300 cm) in a long-term field experiment with a winter wheat-summer maize rotation system, and four N application rates (0; 200; 400 and 600 kg N ha(-1) year(-1)) in the North China Plain. The gas samples were taken twice a week and analyzed by gas chromatography. GHG production and consumption in soil layers were inferred using Fick's law. Results showed nitrogen application significantly increased N2O fluxes in soil down to 90 cm but did not affect CH4 and CO2 fluxes. Soil moisture played an important role in soil profile GHG fluxes; both CH4 consumption and CO2 fluxes in and from soil tended to decrease with increasing soil water filled pore space (WFPS). The top 0-60 cm of soil was a sink of atmospheric CH4, and a source of both CO2 and N2O, more than 90% of the annual cumulative GHG fluxes originated at depths shallower than 90 cm; the subsoil (>90 cm) was not a major source or sink of GHG, rather it acted as a 'reservoir'. This study provides quantitative evidence for the production and consumption of CH4, CO2 and N2O in the soil profile.