Trade-off between soil organic carbon sequestration and nitrous oxide emissions from winter wheat-summer maize rotations: Implications of a 25-year fertilization experiment in Northwestern China

Nitrous oxide emissions and soil profile responses to manure substitution in the North China Plain drylands

Substituting synthetic fertilizers with manures in agriculture enhances soil properties and crop yield. However, the impact on nitrous oxide (N2O) emissions, especially from the soil profile, remains poorly understood. This study examined emissions from 2017 to 2019 on a well-established (>10-year) maize field site in the North China Plain. Three treatments were compared: 100 % synthetic nitrogen (NPK), 50 % synthetic fertilizer N + 50 % manure N substitution (50%MNS), and 100 % manure N substitution (100%MNS). N2O emissions were monitored for three years, and in 2019, N2O concentrations at 20 cm and 40 cm soil depths were analyzed in relation to surface N2O fluxes and environmental factors. The results showed manure substitution resulted in about 13.8 %-25.2 % (50%MNS) and 40.3 %-72.2 % (100%MNS) reduction in N2O emissions over the 3-year period compared with the NPK treatment. Throughout the maize growing season, the top-dressing accompanied by rainfall was responsible for the N2O emissions. The difference in N2O concentrations between all the treatments at 20 cm depth was insignificant, but at 40 cm depth the N2O concentrations were significantly higher for the 50%MNS treatment than the other treatments. The N2O fluxes and N2O concentration were not synchronized especially in NPK. The decoupled relationship between the N2O fluxes and the N2O concentration in the soil profile depth suggested the contribution of N2O produced in the soil profile to the surface N2O fluxes is limited. This study highlights that manure substitution is an efficient measure to reduce N2O emissions.

Modeling lateral carbon fluxes for agroecosystems in the Mid-Atlantic region: Control factors and importance for carbon budget

Estimating lateral carbon fluxes in agroecosystems presents challenges due to intricate anthropogenic and biophysical interactions. We used a modeling technique to enhance our comprehension of the determinants influencing lateral carbon fluxes and their significance in agroecosystem carbon budgets. The SWAT-C model was refined by incorporating a dynamic dissolved inorganic carbon (DIC) module, enhancing our ability to accurately quantify total lateral carbon fluxes. This improved model was calibrated using observed data on riverine particulate organic carbon (POC) and dissolved organic carbon (DOC) fluxes, as well as net ecosystem exchange (NEE) data monitored by a flux tower situated in a representative agricultural watershed, the Tuckahoe Watershed (TW) of the Chesapeake Bay's coastal plain. We assessed the losses of POC, DOC, and DIC across five primary rotation types: C (continuous carbon), CS (corn-soybean), CSS (corn-soybean-soybean), CWS (corn-wheat-soybean), and CWSCS (corn-wheat-soybean-corn-soybean). Our study revealed notable variations in the average annual fluxes of POC (ranging between 152 and 198 kg ha-1), DOC (74-85 kg ha-1), and DIC (93-156 kg ha-1) across the five rotation types. The primary influencing factor for annual POC fluxes was identified as sediment yield. While both annual DOC and DIC fluxes displayed a marked correlation with surface runoff across all crop rotation schemes, soil respiration also significantly influenced annual DIC fluxes. Total lateral carbon fluxes (POC + DOC+DIC) constituted roughly 11 % of both net ecosystem production (NEP) and NEE, yet they represented a striking 95 % of net biome production (NBP) in the TW's agroecosystem. Grain yield carbon accounted for 80 % of both NEP and NEE and was nearly seven times that of NBP. Our findings suggest that introducing soybeans into cornfields tends to reduce NEP, NEE, and also NBP. Conversely, integrating winter wheat into the corn-soybean rotation significantly boosted NEP, NEE, and NBP values, with NBP even surpassing the levels in continuous corn cultivation.

Mitigating greenhouse gas emissions by replacing inorganic fertilizer with organic fertilizer in wheat-maize rotation systems in China

Combining organic and inorganic fertilizer applications can help reduce inorganic fertilizer use and increase soil fertility. However, the most suitable proportion of organic fertilizer is unknown, and the effect of combining organic and inorganic fertilizers on greenhouse gas (GHG) emissions is inconclusive. This study aimed to identify the optimum ratio of inorganic fertilizer to organic fertilizer in a winter wheat-summer maize cropping system in northern China to achieve high grain yields and low GHG intensities. The study compared six fertilizer treatments: no fertilization (CK), conventional inorganic fertilization (NP), and constant total nitrogen input with 25% (25%OF), 50% (50%OF), 75% (75%OF), or 100% (100%OF) organic fertilizer. The results showed that the 75%OF treatment increased the winter wheat and summer maize yields the most, by 7.2-25.1% and 15.3-16.7%, respectively, compared to NP. The 75%OF and 100%OF treatments had the lowest nitrous oxide (N2O) emissions, 187.3% and 200.2% lower than the NP treatment, while all fertilizer treatments decreased methane (CH4) absorption (by 33.1-82.0%) compared to CK. Carbon dioxide flux increased in the summer maize growing season (by 7.7-30.5%) compared to CK but did not significantly differ between fertilizer treatments. The average global warming potential (GWP) rankings across two wheat-maize rotations were NP > 50%OF > 25%OF > 100%OF > 75%OF > CK, and greenhouse gas intensity (GHGI) rankings were NP > 25%OF > 50%OF > 100%OF > 75%OF > CK. We recommend using 75% organic fertilizer/25% inorganic fertilizer to reduce GHG emissions and ensure high crop yields in wheat-maize rotation systems in northern China.

Personal and Professional Mitigation Behavioral Intentions of Agricultural Experts to Address Climate Change

Mitigation activities, whether at the personal level relating to lifestyle or on the professional level, especially in the agriculture sector, are widely encouraged by scientists and policymakers. This research empirically analyses the association between agricultural experts' perceptions about climate change and their intention to implement climate change mitigation. Based on survey data, individuals' reported intention to implement personal and professional mitigation behavior is explained using a conceptual model. The structural equation modeling results suggest that the new ecological paradigm (NEP), institutional trust, and risk salience indirectly influence climate change mitigation intentions. The findings indicate that risk perception, personal efficacy, responsibility, belief in climate change occurring, and low psychological distance trigger a significantly greater intention to support personal and professional mitigation behaviors. However, the research framework is much stronger at predicting the intention to mitigate climate change in professional affairs compared to personal activities. The findings suggest that hypothetical distance factors only have a moderating effect on the relationship between higher climate change environmental values, institutional trust, risk salience, and mitigation intention. This paper analytically explores the regulating role of risk perception, hypothetical distance, personal efficacy, and responsibility between institutional trust, risk salience, and the NEP as independent concepts and intention to personal and professional mitigation behaviors as dependent variables. The findings of the study have important implications for encouraging personal and professional mitigation behaviors.

Pronounced temporal changes in soil microbial community and nitrogen transformation caused by benzalkonium chloride

As one typical cationic disinfectant, quaternary ammonium compounds (QACs) were approved for surface disinfection in the coronavirus disease 2019 pandemic and then unintentionally or intentionally released into the surrounding environment. Concerningly, it is still unclear how the soil microbial community succession happens and the nitrogen (N) cycling processes alter when exposed to QACs. In this study, one common QAC (benzalkonium chloride (BAC) was selected as the target contaminant, and its effects on the temporal changes in soil microbial community structure and nitrogen transformation processes were determined by qPCR and 16S rRNA sequencing-based methods. The results showed that the aerobic microbial degradation of BAC in the two different soils followed first-order kinetics with a half-life (4.92 vs. 17.33 days) highly dependent on the properties of the soil. BAC activated the abundance of N fixation gene (nifH) and nitrification genes (AOA and AOB) in the soil and inhibited that of denitrification gene (narG). BAC exposure resulted in the decrease of the alpha diversity of soil microbial community and the enrichment of Crenarchaeota and Proteobacteria. This study demonstrates that BAC degradation is accompanied by changes in soil microbial community structure and N transformation capacity.

Effects of the fungicide trifloxystrobin on the structure and function of soil bacterial community

Trifloxystrobin has been widely applied to prevent fungal diseases because of its high efficiency and desirable safety characteristics. In the present study, the effects of trifloxystrobin on soil microorganisms were integrally investigated. The results showed that trifloxystrobin inhibited urease activity, promoted dehydrogenase activity. Downregulated expressions of the nitrifying gene (amoA), denitrifying genes (nirK and nirS), and carbon fixation gene (cbbL) were also observed. Soil bacterial community structure analysis showed that trifloxystrobin changed the abundance of bacteria genera related to nitrogen and carbon cycle in soil. Through the comprehensive analysis of soil enzymes, functional gene abundance, and soil bacterial community structure, we concluded that trifloxystrobin inhibited both nitrification and denitrification of soil microorganisms, and also diminished the carbon-sequestration ability. Integrated biomarker response analysis showed that dehydrogenase and nifH were the most sensitive indicators of trifloxystrobin exposure. It provides new insights about trifloxystrobin environmental pollution and its influence on soil ecosystem.

Di-n-butyl phthalate stress induces changes in the core bacterial community associated with nitrogen conversion during agricultural waste composting

Nitrogen (N) loss during composting reduces the quality of compost products and causes secondary environmental pollution. Phthalate esters (PAEs) are common pollutants in agricultural wastes. However, little information is currently available on how PAEs affect N conversion during agricultural waste composting. This research systematically analyzed the impact of di-n-butyl phthalate (DBP) pollution on the N conversion and its related microbial community during composting. Our results indicated that DBP stress results in a shorter thermophilic phase, and then slower compost maturation during composting. Notably, DBP stress inhibited the conversion of ammonia to nitrate, but increased the release of NH₃ and N₂O leading to an increased N loss and an elevated greenhouse effect. Furthermore, DBP exposure led to a reduction of bacteria related to NH₄⁺ and NO₃^- conversion and altered the network complexity of the bacterial community involved in N conversion. It also reduced the abundance of a major nitrification gene (amoA) (P < 0.01) and increased the abundance of denitrification genes (nirK and norB) (P < 0.05). Moreover, DBP affected the overall microbial community composition at all tested concentrations. These findings provide theoretical and methodological basis for improving the quality of PAE-contaminated agricultural waste compost products and reducing secondary environmental pollution.

Carbon farming: Are soil carbon certificates a suitable tool for climate change mitigation?

Increasing soil organic carbon (SOC) stocks in agricultural soils removes carbon dioxide from the atmosphere and contributes towards achieving carbon neutrality. For farmers, higher SOC levels have multiple benefits, including increased soil fertility and resilience against drought-related yield losses. However, increasing SOC levels requires agricultural management changes that are associated with costs. Private soil carbon certificates could compensate for these costs. In these schemes, farmers register their fields with commercial certificate providers who certify SOC increases. Certificates are then sold as voluntary emission offsets on the carbon market. In this paper, we assess the suitability of these certificates as an instrument for climate change mitigation. From a soils' perspective, we address processes of SOC enrichment, their potentials and limits, and options for cost-effective measurement and monitoring. From a farmers' perspective, we assess management options likely to increase SOC, and discuss their synergies and trade-offs with economic, environmental and social targets. From a governance perspective, we address requirements to guarantee additionality and permanence while preventing leakage effects. Furthermore, we address questions of legitimacy and accountability. While increasing SOC is a cornerstone for more sustainable cropping systems, private carbon certificates fall short of expectations for climate change mitigation as permanence of SOC sequestration cannot be guaranteed. Governance challenges include lack of long-term monitoring, problems to ensure additionality, problems to safeguard against leakage effects, and lack of long-term accountability if stored SOC is re-emitted. We conclude that soil-based private carbon certificates are unlikely to deliver the emission offset attributed to them and that their benefit for climate change mitigation is uncertain. Additional research is needed to develop standards for SOC change metrics and monitoring, and to better understand the impact of short term, non-permanent carbon removals on peaks in atmospheric greenhouse gas concentrations and on the probability of exceeding climatic tipping points.

Management Strategies to Mitigate N2O Emissions in Agriculture

The concentration of greenhouse gases (GHGs) in the atmosphere has been increasing since the beginning of the industrial revolution. Nitrous oxide (N2O) is one of the mightiest GHGs, and agriculture is one of the main sources of N2O emissions. In this paper, we reviewed the mechanisms triggering N2O emissions and the role of agricultural practices in their mitigation. The amount of N2O produced from the soil through the combined processes of nitrification and denitrification is profoundly influenced by temperature, moisture, carbon, nitrogen and oxygen contents. These factors can be manipulated to a significant extent through field management practices, influencing N2O emission. The relationships between N2O occurrence and factors regulating it are an important premise for devising mitigation strategies. Here, we evaluated various options in the literature and found that N2O emissions can be effectively reduced by intervening on time and through the method of N supply (30–40%, with peaks up to 80%), tillage and irrigation practices (both in non-univocal way), use of amendments, such as biochar and lime (up to 80%), use of slow-release fertilizers and/or nitrification inhibitors (up to 50%), plant treatment with arbuscular mycorrhizal fungi (up to 75%), appropriate crop rotations and schemes (up to 50%), and integrated nutrient management (in a non-univocal way). In conclusion, acting on N supply (fertilizer type, dose, time, method, etc.) is the most straightforward way to achieve significant N2O reductions without compromising crop yields. However, tuning the rest of crop management (tillage, irrigation, rotation, etc.) to principles of good agricultural practices is also advisable, as it can fetch significant N2O abatement vs. the risk of unexpected rise, which can be incurred by unwary management.

Initial soil conditions outweigh management in a cool-season dairy farm's carbon sequestration potential

Pastures and rangelands are a dominant portion of global agricultural land and have the potential to sequester carbon (C) in soils, mitigating climate change. Management intensive grazing (MIG), or high density grazing with rotations through paddocks with long rest periods, has been highlighted as a method of enhancing soil C in pastures by increasing forage production. However, few studies have examined the soil C storage potential of pastures under MIG in the northeastern United States, where the dairy industry comprises a large portion of agricultural use and the regional agricultural economy. Here we present a 12-year study conducted in this region using a combination of field data and the denitrification and decomposition (DNDCv9.5) model to analyze changes in soil C and nitrogen (N) over time, and the climate impacts as they relate to soil carbon dioxide (CO₂) and nitrous oxide (N₂O) fluxes. Field measurements showed: (1) increases in soil C in grazed fields under MIG (P = 0.03) with no significant increase in hayed fields (P = 0.55); and (2) that the change in soil C was negatively correlated to initial soil C content (P = 0.006). Modeled simulations also showed fields that started with relatively less soil C had significant gains in C over the course of the study, with no significant change in fields with higher initial levels of soil C. Sensitivity analyses showed the physiochemical status of soils (i.e., soil C and clay content) had greater influence over C storage than the intensity of grazing. More extensive grazing methods showed very little change in soil C storage or CO₂ and N₂O fluxes with modeled continuous grazing trending towards declines in soil C. Our study highlights the importance of considering both initial system conditions as well as management when analyzing the potential for long-term soil C storage.

Optimizing organic amendment applications to enhance carbon sequestration and economic benefits in an infertile sandy soil

A thorough understanding of the agricultural, ecological, and economic benefits of organic amendment (OA) application in infertile soils is crucial for facilitating agricultural sustainability. We conducted a three-year field study to evaluate the effects of OA application on soil organic carbon (SOC) sequestration, crop yields, and the net ecosystem economic benefit (NEEB) in a typical infertile sandy soil (with an initial SOC content of 2.56 g kg^-1) of the ancient Yellow River alluvial plain. In addition to the control (CK; non-OA application), two types of OAs, namely, manure-based organic fertilizer (M) and spent mushroom residue (MR), were each applied at 12, 24, and 36 Mg ha^-1 yr^-1. Two scenarios of OA application practices, namely, conventional manual OA application (AMA) and mechanical OA application (AME), were considered in the economic evaluation. An increase of 1 g kg^-1 SOC content could improve the crop yield by 2.25 Mg ha^-1 yr^-1. Compared with the CK, the application of OAs enhanced the SOC content and SOC stock by 14.6%-39.8% and 8.5%-28.2%, respectively. However, the SOC sequestration efficiency of the OAs tended to decrease under high rates of OA application. MR was observed to have greater potential than M in sequestering SOC and promoting soil aggregates. OA-induced SOC sequestration could neutralize 36.6%-97.8% of greenhouse gas emissions, which resulted in a reduction in the global warming potential and its cost by 0.62-2.68 Mg CO₂-eq ha^-1 yr^-1 and 15.46-65.78 CNY ha^-1 yr^-1, respectively. Nevertheless, in terms of the NEEB, the benefits of OA application on crop yield and SOC sequestration were largely offset by the increased material and labor costs. Compared with AMA, AME could save 10%-27% of agricultural costs. The AME of MR at a rate of 24 Mg ha^-1 yr^-1 achieved the highest NEEB. The results of this study suggest that a strategy involving the appropriate OA, optimal application rate, and cheapest incorporation cost for a specific individual soil should be adopted to achieve a sustainable solution for promoting crop productivity, enhancing SOC sequestration, and ensuring farmer income in infertile farming regions.

Effects of cloransulam-methyl and diclosulam on soil nitrogen and carbon cycle-related microorganisms

Cloransulam-methyl and diclosulam are applied to soybean fields to control broad-leaved weeds. These herbicides have become a focus of attention because of their low application dose and high-efficiency advantages. However, the effects of these two herbicides on soil microorganisms are unknown. The present study investigated the effects of 0.05, 0.5, and 2.5 mg kg^-1 of cloransulam-methyl or diclosulam on soil microbes after 7, 14, 28, 42, and 56 days of exposure. The results showed that the two herbicides increased the abundances of functional bacteria related to pesticide degradation. Based on the genetic expression results, we speculated that 0.05 mg kg^-1 of these two herbicides inhibited the nitrification reaction but promoted the denitrification reaction. Diclosulam at a concentration of 0.5 mg kg^-1 may enhance the ability of microbes to fix carbon. β-glucosidase activity was activated by the two herbicides at a concentration of 2.5 mg kg^-1. Diclosulam had a positive effect on urease, but cloransulam-methyl activated urease activity only at concentrations of 0.05 and 0.5 mg kg^-1. The results of the integrated biomarker response showed that the toxicity of diclosulam was greater than that of cloransulam-methyl. Our research provides data for evaluating the environmental risks of cloransulam-methyl and diclosulam.

Greenhouse gas emissions from inorganic and organic fertilizer production and use: A review of emission factors and their variability

Fertilizers have become an essential part of our global food supply chain and are necessary to sustain our growing population. However, fertilizers can also contribute to greenhouse gas (GHG) emissions, along with other potential nutrient losses in the environment, e.g. through leaching. To reduce this environmental impact, tools such as life cycle assessments and decision support systems are being used to aid in selecting sustainable fertilization scenarios. These scenarios often include organic waste-derived amendments, such as manures, composts and digestates. To produce an accurate assessment and comparison of potential fertilization scenarios, these tools require emission factors (EFs) that are used to estimate GHG emissions and that are an integral part of these analyses. However, such EFs seem to be very variable in nature, thereby often resulting in high uncertainty on the outcomes of the analyses. This review aims to identify ranges and sources of variability in EFs to provide a better understanding of the potential uncertainty on the outcomes, as well as to provide recommendations for selecting EFs for future studies. As such, an extensive review of the literature on GHG emissions from production, storage, transportation and application of synthetic fertilizers (N, P, K), composts, digestates and manures was performed. This paper highlights the high variability that is present in emissions data and confirms the great impact of this uncertainty on the quality and validity of GHG predictions related to fertilizers. Variability in EFs stem from the energy source used for production, operating conditions, storage systems, crop and soil type, soil nutrient content, amount and method of fertilizer application, soil bacterial community, irrigation method, among others. Furthermore, a knowledge gap exists related to EFs for potassium fertilizers and waste valorization (anaerobic digestion/composting) processes. Overall, based on this review, it is recommended to determine EFs on a case by case basis when possible and to use uncertainty analyses as a tool to better understand the impact of EF variability.

Nitrogen use efficiency, crop water productivity and nitrous oxide emissions from Chinese greenhouse vegetables: A meta-analysis

Greenhouse vegetable cultivation is a substantial source of nitrous oxide (N₂O) emissions in China due to intensive managements with nitrogen (N) fertilizers and irrigation water. We hypothesize that reducing input rates of N fertilizers or irrigation water to optimal levels would mitigate N₂O emissions without significant loss of vegetable yields. The primary aims of this study are to (i) quantify the variations in vegetable yields, N₂O emissions, nitrogen use efficiency (NUE) and crop water productivity (CWP) under greenhouse cultivation conditions; (ii) determine the major regulating factors of vegetable yields, N₂O emissions, emission factors (EFs), yield-scaled N₂O emissions, NUEs and CWPs; and (iii) evaluate the effectiveness of fertilization and irrigation strategies for N₂O mitigation. We compiled a comprehensive dataset from 44 peer-reviewed publications, which includes 408 determinations of seasonal N₂O emissions from greenhouse vegetable systems across China between 2006 and 2019. An emission coefficient of 0.95% was obtained as the slope of the linear regression between N₂O emissions against N input rates (r² = 0.480, n = 322, p < 0.001) for treatments that were unfertilized and fertilized with conventional fertilizers. For fruit vegetables, N₂O emissions responded to NUEs following a linear-plateau model (r² = 0.539, n = 115, p < 0.001), which suggests that management practices aiming to increase NUEs are effective for decreasing N₂O emissions at NUEs below 0.15 t kg^-1. The results of meta-analyses revealed that applications of biochar or enhanced efficiency fertilizers (EEFs) decreased EFs and yield-scaled N₂O emissions (ranging from -42% to -34%) but did not significantly increase NUEs. Reducing the input rates of N fertilizers (approximately 50% of the total N input) or irrigation water (approximately 20% of the full irrigation water) provided advantages for maintaining vegetable yields (ranging from -7% to 3%), decreasing N₂O emissions (ranging from -68% to -59%), increasing NUEs (ranging from 76% to 157%), and subsequently reducing the reactive N released into the environment.

Effect of organic amendments on yield-scaled N2O emissions from winter wheat-summer maize cropping systems in Northwest China

The effect of dairy manure amendments to agricultural soil on the yield-scaled nitrous oxide (N2O) emissions remains unclear. We hypothesize that an optimum ratio of dairy manure to synthetic fertilizers leads to large nitrogen use efficiency (NUE) and small yield-scaled N2O emissions. The aims of this study were to (1) quantify the variations in the crop yields and N2O emissions from winter wheat-summer maize cropping systems in Northwest China, (2) determine the responses of the NUE and yield-scaled N2O emission to the ratio of organic materials to synthetic fertilizers, and (3) evaluate the relationship between the NUE and yield-scaled N2O emissions. Field measurements were conducted within long- and short-term fertilization experiments between the years of 2014 and 2016. Treatments included synthetic fertilizers, synthetic fertilizers plus crop residues, and synthetic fertilizers plus dairy manure at both sites. The annual grain yields and N2O emissions varied from 13.3 to 18.0 Mg ha-1 and from 1.3 to 3.6 kg N ha-1, respectively, across the treatments. The yield-scaled N2O emissions related negatively to the NUE, suggesting that agronomic aims of improving NUE are an effective approach to mitigate N2O emissions. The ratio of organic materials to synthetic fertilizers was not a significant limit on the NUE and yield-scaled N2O emissions. We conclude that organic amendments appeared to play a minor influence on the promotion of the NUE and N2O mitigation.

Crop yield and N2O emission affected by long-term organic manure substitution fertilizer under winter wheat-summer maize cropping system

Application of organic manure combined with synthetic fertilizer can maintain crop yield and improve soil fertility, but the long-term effects of substituting different proportions of synthetic fertilizers with organic manure on N₂O emission remain unclear. In this study, field experiments and DNDC model simulations were used to study the long-term effects of substituting synthetic fertilizers with organic manure on crop yield and N₂O emission. The field experiment was conducted at Guanzhong Plain, northern China, under a wheat-maize cropping system. Six treatments were included: no fertilization (CK); synthetic nitrogen (N), phosphorus (P) and potassium (K) fertilizers (NPK); and 25%, 50%, 75% and 100% of the synthetic N substituted by dairy manure (25%M, 50%M, 75%M, and 100%M), respectively. The DNDC model was calibrated using the field data from the NPK treatment from 2014 to 2017 and was validated for the other treatments. The results showed that the DNDC model can successfully simulate the crop yield (e.g. nRMSE < 5%) and annual N₂O emission (nRMSE < 20%). In addition, a 30-year simulation found that organic manure substitution treatments could maintain wheat yield well, and the yield variation between different years was small. However, relative to the NPK treatment, the maize yields for the first 6 and 7 years were lower under 50%M and 75%M, and under 100%M maize yields were reduced for the first 15 years. The long-term simulation showed that N₂O emission of fertilized treatment had an increasing trend over time, especially the 75%M treatment where the N₂O emission was higher than that of NPK treatment after 25 years of fertilization. The annual mean N₂O emission under different treatments was, in decreasing order, NPK > 25%M > 50%M > 75%M > 100%M > CK. The yield-scale N₂O emission and emission factor were highest for the NPK treatment. Considering crop yield, yield stability and N₂O emission, substitution of 25% synthetic fertilizer by organic manure can simultaneously ensure crop productivity and environmental protection under the tested environment.

Long-term manure application increased greenhouse gas emissions but had no effect on ammonia volatilization in a Northern China upland field

The impacts of manure application on soil ammonia (NH₃) volatilization and greenhouse gas (GHG) emissions are of interest for both agronomic and environmental reasons. However, how the swine manure addition affects greenhouse gas and N emissions in North China Plain wheat fields is still unknown. A long-term fertilization experiment was carried out on a maize-wheat rotation system in Northern China (Zea mays L-Triticum aestivum L.) from 1990 to 2017. The experiment included four treatments: (1) No fertilizer (CK), (2) single application of chemical fertilizers (NPK), (3) NPK plus 22.5t/ha swine manure (NPKM), (4) NPK plus 33.7t/ha swine manure (NPKM+). A short-term fertilization experiment was conducted from 2016 to 2017 using the same treatments in a field that had been abandoned for decades. The emissions of NH₃ and GHGs were measured during the wheat season from 2016 to 2017. Results showed that after long-term fertilization the wheat yields for NPKM treatment were 7105kg/ha, which were higher than NPK (3880kg/ha) and NPKM+ treatments (5518kg/ha). The wheat yields were similar after short-term fertilization (6098-6887kg/ha). The NH₃-N emission factors (EF_amm) for NPKM and NPKM+ treatments (1.1 and 1.1-1.4%, respectively) were lower than NPK treatment (2.2%) in both the long and short-term fertilization treatments. In the long- and short-term experiments the nitrous oxide (N₂O) emission factors (EF_nit) for NPKM+ treatment were 4.2% and 3.7%, respectively, which were higher than for the NPK treatment (3.5% and 2.5%, respectively) and the NPKM treatment (3.6% and 2.2%, respectively). In addition, under long and short-term fertilization, the greenhouse gas intensities for the NPKM+ treatment were 33.7 and 27.0kg CO₂-eq/kg yield, respectively, which were higher than for the NPKM treatment (22.8 and 21.1kg CO₂-eq/kg yield, respectively). These results imply that excessive swine manure application does not increase yield but increases GHG emissions.