Soil CO2 Emissions Research Articles

Tillage Practices and Liming: Comparative Study of Soil Properties and Forage Corn Production

Tillage conservation practices (CA), traditional agriculture (TA), and liming influence soil properties and crop yield. However, it is essential to demonstrate which tillage and liming practices improve soil properties and forage corn yield. This study compared soil properties and forage corn production in two tillage systems with the addition of dolomite and lime, which formed four treatments. The tillage in the first three days surpassed the TA soil CO2 emission, with 64.8% more CO2 than in the CA soil, and the TA hydraulic conductivity and bulk density were more suitable than those in the CA soil. The CA soil had 233 earthworms m−2 more than in TA. The TA green forage corn yielded 6.45 t ha−1 more than in CA, with a higher P, Ca, and Mg foliar content than in CA, but in the CA, the foliar N and K were higher than in TA. The liming increased soil cations (except K), highlighting the lime on dolomite with—52% Al and + 4.85 t ha−1 of forage corn compared to the control. Soil CO2 emission was far lower in CA than in TA, with a slightly lower forage yield, and other soil properties were improved, meaning lower land preparation costs and time savings than in TA. Lime improved acidic soil faster than dolomite, generating higher forage yields.

Post-fire soil greenhouse gas fluxes in boreal Scots pine forests–Are they affected by surface fires with different severities?

Although forest fires are one of the main natural disturbance types in boreal forests, there is limited information regarding surface fires (dominant in Northern Europe), and how surface fires of different severities could affect post-fire soil greenhouse gas emissions. The results of our study show that fire severity, time since fire and post-fire changes in soil temperature were the main factors driving soil carbon dioxide (CO2) flux (forest floor ecosystem respiration) from burned boreal forest soils. Approximately two hours after the fire, soil CO2 emissions from burned areas were significantly higher compared to pre-fire conditions, and areas with high-severity fires had significantly higher soil CO2 emissions compared to those with low-severity fires. Later (days, months) after the fire, the unburned control areas always had higher soil CO2 emission values compared to burned areas. In the case of methane (CH4), time since fire and post-fire changes in soil temperatures were the main factors driving soil CH4 fluxes. Unburned study areas were sinks of CH4 through the entire measurement period, while immediately after the fire, the burned areas turned from CH4 sink to CH4 source. For nitrous oxide (N2O) measurements, time since fire was the only factor that significantly affected soil N2O fluxes. Shortly after the fire, N2O emissions increased significantly from both low- and high-intensity study plots. Two days after the fire, post-fire soil C and N content decreased in the O-horizon and increased within the first 5 cm of the soil mineral layer, and the trend was visible both in low- and high-severity fire plots. Samples collected four months after the fire, showed similar total soil C and N content as there was before the fire.

Regional emissions of soil greenhouse gases across Tibetan alpine grasslands

Soil greenhouse gas (GHG) emissions play an important role in regional climate feedback on the Qinghai-Tibetan Plateau (QTP). Previous studies have focused on soil GHGs based on observations within a limited space on the QTP, however, the regional GHG emissions remain unclear. Analyzing soil samples from 25 sites along a 2,700 km transect across QTP, we showed significantly higher soil CO2 and N2O emission rates in alpine meadows than other upland grassland types, but similar soil CH4 uptake rates across all grassland types. The spatial variations of total soil GHG balance were dominated by CO2 emission. We found that CO2 emission was primarily constrained by high soil pH, low soil moisture and nutrient availability, and fungal abundance, N2O emission was inhibited by high soil pH, while CH4 uptake was dominated by methanotrophic abundance. Furthermore, we estimated a current regional total soil GHG balance of 144.4 Tg CO2-eq yr−1 for surface soil across Tibetan alpine grasslands, which increased by 17.6%, 24.8%, and 38.9% under warming scenarios of 1.5℃, 2℃ and 3℃, respectively. Our results provide a baseline for regional soil GHG emissions responding to climate warming on the QTP.

Impact of Organic Vegetable System on Soil Organic Matter Pools and CO2 Emission in the Tropical Region

ABSTRACT It is widely recognized that the input of organic matter in tropical agriculture is essential to maintain productivity and soil quality. This study aimed to investigate the dynamics of organic C pools and CO2 emission influenced by organic compost fertilization and leucaena biomass in an area of 6 years under organic farming. The system consisted of 5 treatments based on 5 levels of fertilization with organic compost (0, 10, 20, 30, and 40 t ha−1). Each block was surrounded by leucaena and their pruning’s were distributed in equal proportions for all treatments. Two rotating crops were performed per year, cabbage/corn. Soil samples were collected in the 0–10 and 10–20 cm layers in 2-year seasons. TOC and N stocks were between 23.1 and 51.6 t ha−1, and 2.1 and 5.4 t ha−1, respectively. The highest compost doses increased the microbial biomass C and N. The increase in microbial biomass was followed by higher emissions of C-CO2. Increased microbial quotient values indicated C accumulation in the system by a higher amount of active metabolic C. The microbial biomass was less efficient in the use of the high organic compost doses. The dose of compost should be reduced and applied constantly by the farmers to attend the plant demand by nutrients and increase the efficiency of C sequestration in the soil. This C sequestration will also improve biological activity and soil quality in tropical regions, increasing food production.

Effects of Organic Matter Addition on Soil Carbon Contents, CO2 Emissions, and Bacterial Compositions in a Paddy Field in South China

Increasing soil organic carbon (SOC) contents and reducing carbon dioxide (CO2) emissions in paddy soil fields can result in positive impacts on climate change mitigation and soil quality. However, SOC accumulation and its microbial driving factors under enhanced fertilization strategies (e.g., organic matter application) are still unclear. Therefore, we investigated the effects of organic matter addition on SOC variations, CO2 fluxes, and their relationships with soil bacterial compositions and functions through a 6-year fertilizer experiment in rice fields involving two fertilization types, namely chemical fertilizer (NPK) and chemical fertilizer combined with organic matter (NPK+OM). The results showed significantly higher and lower SOC contents (p < 0.05) in the 10–20 cm soil layer under the NPK+OM treatment before rice transplanting and after rice harvest, respectively, than those under the NPK treatment. The lower SOC contents after rice harvest might be due to the great nutrient consumption, resulting in higher rice yields in the NPK+OM than those in the NPK treatment by 6.68 to 32.35%. Compared with NPK, NPK+OM reduced the in-situ CO2 fluxes by 38.70–118.59%. However, the ex-situ SOC mineralization rates were not affected by NPK+OM in the 0–10 and 10–20 cm soil layers. The 16S rRNA sequence indicated a significant increase in the abundance of non-singleton amplicon sequence variants (ASVs) in the NPK+OM treatment scenario compared to those in the NPK treatment scenario. The top three most important soil bacterial phylum influenced by NPK+OM were LCP-89, BRC1, and Rokubacteria in April, as well as Firmicutes, Nitrospinae, and BRC1 in July. Soil Actinobacteria was negatively correlated with the SOC contents in April and July. The results of the present study demonstrate the economic and ecological benefits of the organic matter addition in rice production, as well as the contribution of soil bacteria to SOC accumulation and CO2 emission reduction.

Soil CO2 emission and stable isotopes (δ13C, δ18O) of CO2 and calcites reveal the fluid origin and thermal energy in the supercritical geothermal system of Krafla, Iceland

The Krafla geothermal system is located within a volcanic center that periodically erupts basaltic lavas, and has recently attracted an economic interest due to supercritical fluids forming near a shallow magma intrusion (∼ 2 km depth). Here, we discuss new soil CO2 flux and stable isotope data of the CO2 efflux (δ13C) and hydrothermal calcites (δ13C, δ18O) of drill cuttings to estimate both the current magmatic outgassing from soils and the thermal flows in the geothermal system. Soil CO2 emission is controlled by tectonics, following the NNE-SSW fissure swarm direction and a WSW-ENE trend, and accounts for ∼62.5 t d−1. While the δ18O of the H2O in equilibrium with deep calcites is predominantly meteoric, both the δ13C of the soil CO2 efflux and of the fluids from which calcite precipitated have a clear magmatic origin, overlapping the δ13C estimated for the Icelandic mantle (−2.5 ± 1.1 ‰). Estimates based on the soil CO2 emission from the southern part of the system show that these fluxes might be sustained by the ascent and depressurization of supercritical fluids with a thermal energy of ∼800 MW. Such significant amount of energy might reach 1.5 GW if supercritical conditions extended below the whole investigated area. Finally, we report an increase in the soil CO2 emission of about 3 times with respect to 14 years ago, likely due to recent changes in the fluid extracted for power production or magmatic activity. Pairing the soil CO2 emission with stable isotopes of the efflux and calcite samples has important implications for both volcano monitoring and geothermal exploration, as it can help us to track magmatic fluid upflows and the associated thermal energy.

Salty bio-converted organic fertilizer modulates soil greenhouse gas emissions

The black soldier fly frass (BSFF) can be applied as a bio-converted organic fertilizer in agriculture and has been shown to affect soil properties and plant growth. However, the impacts of salty BSFF derived from kitchen waste (KW) on soil properties and greenhouse gas emissions are unclear. The impacts of salty black soldier fly (Hermetia illucens) frass derived from KW on soil properties and greenhouse gas emissions were investigated. The frass amendments increased soil dissolved organic carbon and nitrogen (0.5–1.6 and 0.1–15 fold) and soil ammonium (0.5–31 fold) content, with a similar trend as soil pH (0∼0.4 fold) and electrical conductivity (2–131 fold). Soil gas emissions (CO2 and N2O) increased by frass amendments. The frass amendment affected the microbial communities followed by the addition rates, with the enriched beneficial bacteria (Nocardioides) and depleted denitrification fungi (Penicillium) as well as the C- and N-cycle related microbial functional genes. The nirS and amoB genes were the critical factors in the soil N2O emission with the frass amendment ratio in the soil. The lig and glx genes involved in lignin decomposition contributing to the increase of soil CO2 emission. These findings indicated that there is a need to inform research and policy decisions aimed at developing and promoting appropriate standards and guidelines for quality production, sustainable utilization, and successful integration of the frass into existing organic fertilizer framework and soil systems.

Seasonal dynamics of soil CO2 emissions from different semi-arid land-use systems

ABSTRACT Soil carbon dioxide (CO2) fluxes are a critical component in understanding carbon sequestration. In sub-Saharan Africa, empirically measured CO2 emissions data from diverse land-use systems is limited. Soil CO2 emission rates were measured in the Limpopo Province, South Africa for 12 months at two-week intervals in natural systems (forest and shrubland) and commercially managed orchards (avocado and citrus) to establish seasonal dynamics of soil CO2 emissions across these land-use systems. The results showed a variation in emission rates with the variation depending on the season. In the spring and winter, soil CO2 emission rates in citrus were four times higher than in the shrubland due to higher moisture levels. However, in the summer season, the forest emission rates were 40% higher than in citrus due to higher soil organic carbon content. Organic carbon stocks were higher in the forest (1.19 kg/m2) compared to the other land uses. This study revealed differences in soil CO2 emission rates among land-use systems, with the cumulative amount of CO2 emitted over a 12-month period following the order: forest (39.3 tons/ha) > citrus (36.1 tons/ha) > shrubland (28.1 tons/ha) > avocado (26.9 tons/ha). Thus, understanding the emission patterns from various ecosystems can inform strategies for mitigating greenhouse gas emissions.

Effects of degradable and non-degradable microplastics and oxytetracycline co-exposure on soil N2O and CO2 emissions

Microplastics and antibiotics are emerging contaminants that can elicit considerable adverse effects on carbon and nitrogen cycles and greenhouse gas emissions. The effect of the combined occurrence of antibiotics and different types of microplastics on soil ecosystem is poorly understood. We investigated the effects of oxytetracycline (OTC), polylactic acid (PLA) microplastics, and polyethylene (PE) microplastics alone and in combination on plant root growth traits, soil extracellular enzymatic activity, and nitrous oxide (N2O) and carbon dioxide (CO2) emissions from the soil. Plant root growth traits including root area, root surface area, root volume and root branches were negatively affected by all treatments; soil extracellular enzymatic activity was also negatively affected by all treatments expect for the cellobiohydrolase. The results showed that CO2 emission increased in all treatments, with a maximum increase of 505 % in the PLA treatment; however, N2O emissions increased in the OTC treatment by 44 % but decreased in all other treatments as compared to the control. Furthermore, partial least squares path modeling analysis suggested that soil extracellular enzymes significantly influenced soil N2O and CO2 emissions (P < 0.05) and had a strong correlation with root growth traits (P < 0.05). We thus concluded that changes in soil extracellular enzymatic activities and plant root growth traits, which were affected by different microplastic and antibiotic treatments, influenced soil CO2 and N2O gas emissions.

The Pulses of Soil CO2 Emission in Response to Rainfall Events in Central Siberia: Revisiting the Overall Frost-Free Season CO2 Flux

Boreal forests nowadays act as a sink for atmospheric carbon dioxide; however, their sequestration capacity is highly sensitive to weather conditions and, specifically to ongoing climate warming. Extreme weather events such as heavy rainfalls or, conversely, heat waves during the growing season might perturb the ecosystem carbon balance and convert them to an additional CO2 source. Thus, there is an urgent need to revise ecosystem carbon fluxes in vast Siberian taiga ecosystems as influenced by extreme weather events. In this study, we focused on the soil CO2 pulses appearing after the rainfall events and quantification of their input to the seasonal cumulative CO2 efflux in the boreal forests in Central Siberia. Seasonal measurements of soil CO2 fluxes (both soil respiration and net soil exchange) were conducted during three consecutive frost-free seasons using the dynamic chamber method. Seasonal dynamics of net soil exchange fluxes demonstrated positive values, reflecting that soil respiration rates exceeded CO2 uptake in the forest floor vegetation layer. Moreover, the heavy rains caused a rapid pulse of soil emissions and, as a consequence, the release of additional amounts of CO2 from the soil into the atmosphere. A single rain event may cause a 5–11-fold increase of the NSE flux compared to the pre-rainfall values. The input of CO2 pulses to the seasonal cumulative efflux varied from near zero to 39% depending on precipitation patterns of a particular season. These findings emphasize the critical need for more frequent measurements of soil CO2 fluxes throughout the growing season which capture the CO2 pulses induced by rain events. This approach has inevitable importance for the accurate assessment of seasonal CO2 soil emissions and adequate predictions of response of boreal pine forests to climatic changes.

Simultaneous achievement of removing bensulfuron-methyl and reducing CO2 emission in paddy soil by Acinetobacter YH0317 immobilized boron-doping biochar

Herbicide residue and greenhouse gas (GHG) emission are two main problems in the paddy rice field, which have barely been considered simultaneously. Herein, a bensulfuron-methyl (BSM)-degrading bacterium named Acinetobacter YH0317 was successfully immobilized on two kinds of biochars and subsequently applied in the paddy soil. The BSM removal rate of Acinetobacter YH0317 immobilized boron-doping biochar (BBC) was 80.42% after 30 d, which was significantly higher than that of BBC (39.05%) and Acinetobacter YH0317 (49.10%) applied alone. BBC acting as an immobilized carrier could enable Acinetobacter YH0317 to work in harsh and complex environment and thus improve the BSM removal efficiency. The addition of Acinetobacter YH0317 immobilized BBC (TP5) significantly improved the soil physicochemical properties (pH, SOC, and NH4+-N) and increased the diversity of soil microbial community compared to control group (CG). Meanwhile, Acinetobacter YH0317 immobilized BBC reduced the CO2-equivalent emission by 41.0%. Metagenomic sequencing results revealed that the decreasing CO2 emission in TP5 was correlated with carbon fixation gene (fhs), indicating that fhs gene may play an important role in reducing CO2 emission. The work presents a practical and supportive technique for the simultaneous achievement on the soil purification and GHG emission reduction in paddy soil.

Key Role of Vegetation Cover in Alleviating Microplastic-Enhanced Carbon Emissions.

Microplastics (MPs) are considered to influence fundamental biogeochemical processes, but the effects of plant residue-MP interactions on soil carbon turnover in urban greenspaces are virtually unknown. Here, an 84-day incubation experiment was constructed using four types of single-vegetation-covered soils (6 years), showing that polystyrene MP (PSMP) pollution caused an unexpectedly large increase in soil CO2 emissions. The additional CO2 originating from highly bioavailable active dissolved organic matter molecules (<380 °C, predominantly polysaccharides) was converted from persistent carbon (380-650 °C, predominantly aromatic compounds) rather than PSMP derivatives. However, the priming effect of PSMP derivatives was weakened in plant-driven soils (resistivity: shrub > tree > grass). This can be explained from two perspectives: (1) Plant residue-driven humification processes reduced the percentage of bioavailable active dissolved organic matter derived from the priming effects of PSMPs. (2) Plant residues accelerated bacterial community succession (dominated by plant residue types) but slowed fungal community demise (retained carbon turnover-related functional taxa), enabling specific enrichment of glycolysis, the citric acid cycle and the pentose phosphate pathway. These results provide a necessary theoretical basis to understand the role of plant residues in reducing PSMP harm at the ecological level and refresh knowledge about the importance of biodiversity for ecosystem stability.

Effects of intercropping on soil greenhouse gas emissions - A global meta-analysis

Diversified cropping systems, such as intercropping, have shown multifunctionality in agronomic productivity promotion, pest control, and soil health improvement. However, the intense interaction between crop species stimulates soil carbon and nitrogen turnover, and intercropping systems cause inexplicit effects on soil greenhouse gas emissions (GHG). Therefore, a comprehensive meta-analysis using 52 published articles (531 paired observations) was conducted to elucidate the effects of intercropping on soil N2O, CO2, and CH4 emissions under different environmental conditions and field practices to identify the primary driving factors, such as climate, soil and field practices. The results showed that intercropping treatment had a non-significant impact on the three GHG emissions on average. However, using a cereal-legume intercropping regime, adopting moderate N application rate or intercropping in alkaline soils could significantly mitigate soil N2O emission. Additionally, intercropping in soils with high soil organic carbon reduce soil CH4 emission. On the contrary, increasing intercropping duration, or adopted in soils with moderate soil total N tended to stimulate CO2 emission. The mixed-effect model selection indicated that initial soil pH, MAP, MAT, tillage regime, and intercropping duration and type were significant moderators in regulating soil GHG emissions. Our findings explicitly elucidated soil GHG responses to intercropping practice. Further studies are warranted on the evaluation of long-term intercropping effects to improve the comprehensive understanding of C and N balance and global warming potential under intercropping.

Effect of short-term nitrogen deposition on dry-wet seasonal variation of soil respiration in degraded Poa pratensis alpine meadow of the Napahai, Yunnan, China.

To explore the coupling of dry-wet seasonal variations of soil respiration with their environmental factors in the alpine meadow under the background of increasing nitrogen (N) deposition, we conducted an experiment in the typical degraded Poa pratensis meadow in the Napahai, Yunnan. There were four treatments, i.e., control (0 g·m-2·a-1), low (5 g·m-2·a-1), medium (10 g·m-2·a-1), and high (15 g·m-2·a-1) levels. We examined the effects of aboveground biomass, plant diversity, and soil physicochemical properties on soil respiration. The results showed that N deposition significantly promoted soil respiration. Compared with that in the control, soil respiration rates increased by 21.9%-53.9% and 27.3%-51.2% in dry and wet seasons, respectively. The maximum value of soil respiration rate was recorded in the medium N treatment. N deposition dramatically elevated aboveground biomass (52.2%-66.4%). Plant diversity declined with increasing N addition levels, with the maximum value (13.5%-24.2%) being recorded in high treatment in wet season. The values of ammonium nitrogen, organic matter, microbial biomass carbon and nitrogen, temperature and moisture in the three N treatments were elevated by 14.3%-333.5% compared with the control, while those of soil pH were decreased by 9.0%-34.6%. Results of the structural equation modelling showed that plant biomass, Shannon diversity, microbial biomass, soil temperature, and moisture showed a positive effect on soil respiration, while bulk density had a negative effect. Soil nitrogen pool and pH were main factors driving soil CO2 emissions, accounting for 55.7% and 45.1% of the variations, respectively. Therefore, short-term atmospheric N deposition stimulated soil respiration primarily via altering soil pH and nitrogen pool components in the degraded alpine meadow.

Effects of Combined Peanut Shell and Biochar Application on Soil Nutrient Content, CO2 Emission, and Bacterial Community in Dryland Red Soil of Southern China

Effects of Combined Peanut Shell and Biochar Application on Soil Nutrient Content, CO2 Emission, and Bacterial Community in Dryland Red Soil of Southern China

Moderate increase of precipitation stimulates CO2 production by regulating soil organic carbon in a saltmarsh.

Saltmarsh is widely recognized as a blue carbon ecosystem with great carbon storage potential. Yet soil respiration with a major contributor of atmospheric CO2 can offset its carbon sink function. Up to date, mechanisms ruling CO2 emissions from saltmarsh soil remain unclear. In particular, the effect of precipitation on soil CO2 emissions is unclear in coastal wetlands, due the lack of outdoor data in real situations. We conducted a 7-year field manipulation experiment in a saltmarsh in the Yellow River Delta, China. Soil respiration in five treatments (-60%, -40%, +0%, +40%, and + 60% of precipitation) was measured in the field. Topsoils from the last 3 years (2019-2021) were analyzed for CO2 production potential by microcosm experiments. Furthermore, quality and quantity of soil organic carbon and microbial function were tested. Results show that only the moderate precipitation rise of +40% induced a 66.2% increase of CO2 production potential for the microcosm experiments, whereas other data showed a weak impact. Consistently, soil respiration was also found to be strongest at +40%. The CO2 production potential is positively correlated with soil organic carbon, including carbon quantity and quality. But microbial diversity did not show any positive response to precipitation sizes. r-/K-strategy seemed to be a plausible explanation for biological factors. Overall, our finding reveal that a moderate precipitation increase, not decrease or a robust increase, in a saltmarsh is likely to improve soil organic carbon quality and quantity, and bacterial oligotroph:copiotroph ratio, ultimately leading to an enhanced CO2 production.

Does no-till crop management mitigate gaseous emissions and reduce yield disparities: An empirical US-China evaluation

Global agricultural systems face one of the greatest sustainability challenges: meeting the growing demand for food without leaving a negative environmental footprint. United States (US) and China are the two largest economies and account for 39 % of total global greenhouse gases (GHG) emissions into the atmosphere. No-till is a promising land management option that allows agriculture to better adapt and mitigate climate change effects compared to traditional tillage. However, the efficacy of no-till for mitigating GHG is still debatable. In this meta-analysis, we comprehensively assess the impact of no-till (relative to traditional tillage) on GHG mitigation potential and crop productivity in different agroecological systems and management regimes in the US and China. Overall, no-till in China did not change crop yields, although soil CO2 (8 %) and N2O (12 %) emissions decreased significantly, while soil CH4 emissions increased by 12 %. In contrast to Chinese no-till, a significant improvement in crop yields (up to 12 %) was recorded on US cropland under no-till. Moreover, significant decreases in soil N2O (21 %) and CH4 (12 %) emissions were observed. Of the three cropping systems, only wheat showed significant reduction in CO2, N2O and CH4 emissions in the Chinese no-till system. In the case of US, no-till soybean-rice and maize cropping systems demonstrated significant emission reductions for N2O and CO2, respectively. Interestingly, yields of no-till maize in China and rice in US exceeded those of other no-till cereals. In China, no-till on medium-texture soils resulted in significant reductions in GHG emissions and higher crop yields compared to other soil types. In both countries, the relatively higher crop yields under irrigated versus non-irrigated no-till and the significant yield differences on fine textured soils under US no-till are likely due to the substantial N2O reductions. In summary, crop yield disparities from no-till between China and the US were related to the insignificant effects on controlling CH4 emissions and successfully mitigating N2O, respectively. This study comprehensively demonstrates how cropping system and pedoclimatic conditions influence the relative effectiveness of no-till in both countries.

Temperature Matters More than Fertilization for Straw Decomposition in the Soil of Greenhouse Vegetable Field

As the largest organic carbon input to agroecosystems, crop straw can solve the problem of soil quality degradation in greenhouse vegetable fields, harmonize the balance between soil nutrients and energy, and improve soil quality to maintain the sustainable production of greenhouse vegetables. However, the microbial mechanism of the straw decomposition process under different temperatures and fertilization treatments in greenhouse vegetable soils has not been clarified. Soil samples were used to investigate the biology of straw decomposition in the soil at three incubation temperatures (15, 25, and 35 °C) through a soil incubation experiment (60 d) under different fertilization treatments. Fertilization treatments for this long-term field experiment included chemical fertilizer (CF), substitution of half of the chemical N fertilizer with manure (CM), straw (CS), or combined manure and straw (CMS). The results showed that soil hydrolase activities tended to decrease with increasing temperature during straw decomposition. Compared with the CF, organic substitutions (CM, CMS, and CS) increased soil β-glucosidase, β-cellobiosidase, N-acetyl-glucosaminidase, and β-xylosidase activities during straw decomposition. Soil CO2 emission rates were the highest at each incubation temperature on the first day, rapidly declining at 25 °C and 35 °C and slowly declining at 15 °C. The soil CO2 cumulative emissions tended to increase with increasing temperature under different fertilization treatments. PCA showed that the responses of soil enzyme activities to temperature at 7, 15, and 30 d of straw decomposition were stronger than those of fertilization. In summary, both fertilization treatment and incubation temperature could influence soil CO2 emissions by affecting soil physicochemical properties and enzyme activities during straw decomposition, whereas incubation temperature had a stronger effect on straw decomposition than fertilization, as indicated by PLS-PM and three-way ANOVA. Considering the influence for fertilization on the straw decomposition process at different incubation temperatures, the straw applications (CMS and CS) were more suitable to temperature changes.

Application of biochar to anaerobic digestion versus digestate: Effects on N emissions and C stability

Research attention is growing for biochar as amendment for anaerobic digestion (AD), as it may improve both the AD process and digestate properties. In this study, two biochars (from insect frass or the woody fraction of green waste, both pyrolyzed at 450 °C) were added (5 % w/w) during semi-continuous AD of organic kitchen waste and chicken manure. Biochar was mixed either during the AD process or to the digestate post-treatment. The impact of biochar addition on the AD process, NH3 and greenhouse gas emissions, as well as C and N mineralization following soil application, was examined. Biochar did not affect the biogas yield, but did lead to a reduction in NH3 levels in the biogas and NH4+-N sorption onto the biochars, reducing the risk of AD inhibition. N sorbed as NH4+-N onto the biochar was more available for mineralization than N sorbed as NH3. N sorption on biochar-amended digestates did not result in trade-offs when these digestates were applied to soil: the sorbed N was not released as NH3 or N2O after soil application and was not released as mineral N in either the short or medium term. The C-rich biochars increased the OC content of the digestate, which enhanced its value as soil improver. Additionally, mixing biochar with digestate decreased the soil CO2 emissions up to 33 % when it was added after AD; no priming effects were observed. These findings highlight the potential benefits of incorporating biochar into AD systems and the subsequent application of biochar-amended digestate in agricultural practices.

Long-term saline water irrigation has the potential to balance greenhouse gas emissions and cotton yield in North China plain

Saline water has proven to be one of the alternative sources of freshwater for agricultural irrigation in water-scarce areas. However, the changes in farmland ecology caused by saline water irrigation remain unclear. In this study, six irrigation water salinities (CK: 1.3 dS m−1, S1: 3.4 dS m−1, S2: 7.1 dS m−1, S3: 10.6 dS m−1, S4: 14.1 dS m−1, S5: 17.7 dS m−1) were set in a three-year (2019, 2021–2022) experiment to investigate their effects on soil environment and greenhouse gas emissions in cotton fields under long-term saline water irrigation. Results show that soil salinity in the same layer increased as increasing water salinity. Soil moisture of S3–S5 increased significantly by 4.99–12.94%. There was no significant difference in soil organic matter content between CK and S1. Saline water irrigation increased soil ammonium nitrogen content by 0.57–49.26%, while decreasing nitrate nitrogen content by 1.43–32.03%. Soil CO2 and N2O emissions and CH4 uptake were lower in S1–S5 than in CK at different cotton growth stages. In addition, saline water irrigation reduced the global warming potential by 6.93–53.86%. A structural equation model was developed to show that soil salinity, moisture, and ammonium nitrogen content were negatively correlated with global warming potential, while organic matter and nitrate nitrogen had positive effects on global warming potential. Considering the comprehensive perspectives of gas emissions and cotton yield, irrigation water with salinity less than 10.6 dS m−1 could effectively reduce greenhouse gas emissions from cotton fields while maintaining stable cotton yields in the experimental area and similar region.