Soil Emissions Research Articles

A high‐frequency greenhouse gas flux analysis tool: Insights from automated non‐steady‐state transparent soil chambers

AbstractNon‐steady‐state chambers are widely employed for quantifying soil emissions of CO2, CH4, and N2O. Automated non‐steady‐state (a‐NSS) soil chambers, when coupled with online gas analysers, offer the ability to capture high‐frequency measurements of greenhouse gas (GHG) fluxes. While these sampling systems provide valuable insights into GHG emissions, they present post‐measurement challenges, including the management of extensive datasets, intricate flux calculations, and considerations for temporal upscaling. In this study, a computationally efficient algorithm was developed to compute instantaneous fluxes and estimate diel flux patterns using continuous, high‐resolution data obtained from an a‐NSS sampling system. Applied to a 38‐day dataset, the algorithm captured concurrent field measurements of CO2, CH4, and N2O fluxes. The automated sampling system enables the acquisition of high‐frequency data, allowing the detection of episodic gas flux events. By using shape‐constrained additive models, a median percentage deviation (bias) of −1.031 and −4.340% was achieved for CO2 and N2O fluxes, respectively. Simpson's rule allowed for efficient upscale from instantaneous to diel flux values. As a result, the proposed algorithm can rapidly and simultaneously calculate CO2, CH4, and N2O fluxes, providing both instantaneous and diel values directly from raw, high‐temporal‐resolution data. These advancements significantly contribute to the field of GHG flux measurement, enhancing both the efficiency and accuracy of calculations for a‐NSS soil chambers and deepening our understanding of GHG emissions and their temporal dynamics.

Effects of Different Living Grass Mulching on Soil Carbon and Nitrogen in an Apple Orchard on Loess Plateau

Living grass mulching (LMG) is a modern, environmentally friendly, practical, and efficient production management technology that improves the ecological environment, quality, and efficiency of the orchard. However, in arid and semi-arid areas, the effects of different grass species mulching on soil carbon composition, carbon pool stability, and nitrogen content are still unclear. Therefore, in order to explore the impact of different LMG on soil carbon, nitrogen, and its component content, as well as the related soil carbon pool management index in an apple orchard located in the semi-arid region of the Loess Plateau, a control experiment was conducted. The experiment involved different grass species cover treatments on an 11-year-old semi-dwarf Qinguan apple orchard from 2019 to 2022. Soil carbon and nitrogen content were measured under each treatment. The results indicated that the application of LMG treatment and depth of the soil had a significant impact on the soil organic carbon (SOC), particulate organic carbon (POC), inactive organic carbon (NAOC), total nitrogen (TN), and carbon-to-nitrogen ratio (C/N). Planting Vulpia myuros mulches significantly enhanced 39.6% surface soil organic carbon, 61.7% surface particulate organic carbon, 20.3% surface dissolved organic carbon (DOC), 75.8% surface inactive organic carbon, and 20.6% surface soil total nitrogen compared to clean tillage. Mulching treatment with the planting of Vulpia myuros boosted surface soil organic carbon and decreased soil carbon pool activity (CPA) and carbon pool activity index (CPAI), ultimately improving the stability of the soil carbon pool. The findings will have a beneficial impact on improving soil quality, carbon sequestration, and emission reduction in arid and semi-arid regions.

Converse Responses of Biochar Application on N2O Emissions in Soils at Different pH Values in a Subtropical Citrus Orchard

The aim of this study was to explore the effect of biochar on N2O emissions in soils with different pH levels. Soils with five pH levels (4.0, 5.1, 5.8, 6.6, and 7.2) were incubated in two conditions, with 0% biochar (CK) and 1% biochar (BC), for 23 days. N2O emissions were measured at nine time points, and soil chemical properties, AOA-amoA, AOB-amoA, nirK, nirS, and nosZ, were analyzed. Partial least squares path modelling (PLS-PM) was used to assess the effect of nitrification and denitrification pathways on potential N2O emissions. The results showed that biochar reduced N2O emissions in highly acidic soil (pH 4.0) but increased emissions in soils with pH values ranging from 5.1 to 7.2. In highly acidic soils, decreased N2O emission was associated with increased soil pH (p < 0.05) and decreased dissolved organic carbon content (p < 0.05), leading to higher nosZ gene abundance (p < 0.05). Meanwhile, in acidic to neutral soils, biochar application increased soil pH (6.6–11.7%), dissolved organic nitrogen (5.9–29.5%), dissolved organic carbon (8.6–41.0%), stimulated AOB-amoA, nirK, nirS gene abundance (p < 0.05), and thus increased N2O emissions. The results verified the influence of nitrification and denitrification genes on N2O production in soils with different pH values. In conclusion, biochar had different effects on N2O emissions based on soil pH, highlighting the need to consider pH when using biochar to mitigate N2O emissions in subtropical citrus orchards.

Invasion of Prosopis trees into arid ecosystem alters soil carbon and nitrogen processes and soil trace gases emissions

The invasion of drylands by leguminous mesquite (Prosopis spp.) is frequently associated with increases in the soil organic carbon (C) and nitrogen (N) pools. These increases stimulate soil microbial activity and accelerate soil C and N cycling. However, the impact of mesquite invasion on soil biogeochemistry, especially the emission of trace gases, in an ecosystem with an already established population of N-fixing plants is not well studied. To fill this knowledge gap, we quantified the in-situ soil trace gas emissions and the potential microbial activity in soils under invasive mesquite (Prosopis juliflora) trees (Prosopis), native acacia (Acacia tortilis) trees (Acacia), and in unvegetated soil between trees (Bare soil) on the western shore of the Dead Sea. To account for contributions of spatial and weather variabilities to the emission processes we conducted measurements across two geographic sites, 45 km apart, over two years, both under naturally dry soil conditions and after soil wetting. Before wetting, soil emissions of carbon dioxide (CO2) and nitric oxide (NOx) followed the order: Acacia > Prosopis ≥ Bare soil, while soil nitrous oxide (N2O) emissions were low and uniform across the three habitats. The soil inorganic N concentration, microbial biomass, and water-extractable organic C were significantly higher under the A. tortilis canopies compared with P. juliflora and Bare soil. After wetting, soil trace gases emissions increased up to 66, 1534, and 42 times, for CO2, N2O, and NOx, respectively, and remained higher under the native A. tortilis than under P. juliflora and Bare soil (Acacia > Prosopis > Bare soil). The potential soil microbial activity, however, was similar between the soils under the tree canopies. Our results show that the establishment of invasive leguminous trees increase soil CO2 and gaseous N emissions relative to the Bare soils, but not relative to native leguminous trees.

An Interseasonal Comparison of Soil Respiration in Xeric and Mesic Pine Forest Ecosystems in Central Siberia

An understanding of how boreal forest composition responds to global environmental changes is an important challenge to predicting the future global carbon balance. Boreal forests are the most significant sink for atmospheric carbon dioxide; however, their sequestration capacity is highly sensitive to ongoing climate changes. The combination of the hydrothermal conditions of a territory strongly regulates its biogeochemical processes. The carbon fluxes in boreal forests are strongly mediated by the ground vegetation cover, composed of mosses (mesic) and lichens (xeric). Despite the concurrence of xeric and mesic vegetation types, their responses to climate variations varies significantly. Soil emission is an informative indicator of ecosystem functioning. In this study, we focused on the soil CO2 dynamics during frost-free seasons with different precipitation regimes in the xeric and mesic boreal ecosystems of Central Siberia. Seasonal measurements of soil CO2 emissions were conducted during frost-free seasons using the dynamic chamber method. Our findings reveal that the precipitation regimes of each year may control the seasonal soil emission dynamics. The soil moisture is the most important driver of emissions growth in the water-limited lichen pine forest (R2adj. = 18%). The soil temperature plays the largest role in the feather moss pine forest during the dry (R2adj. = 31%) seasons, and in the lichen pine forest during the wet (R2adj. = 41%) seasons. The cumulative efflux for the xeric and mesic sites is mostly related to the hydrothermal conditions, and not to the differences in ground vegetation cover. During the dry seasons, on average, the soil CO2 emissions are 45% lower than during the wet seasons for both sites. These findings emphasize the need for estimating and including the hydrothermal characteristics of the growing season for detailed emission assessments.

Insights into effects of conventional and biodegradable microplastics on organic carbon decomposition in different soil aggregates

The impacts of microplastics on soil ecological functions such as carbon recycling and soil structure maintenance have been extensively focused. However, the mechanisms underlying the impacts of microplastics on soil carbon transformation and soil microbial community at soil aggregate scale have not been clarified yet. In this work, the effects and action mechanisms of traditional microplastic polypropylene (PP) and degradable microplastic polylactic acid (PLA) on carbon transformation in three sizes of soil aggregates were investigated. The results showed that both PP and PLA promoted CO2 emission, and the effect depended on the type and content of microplastics, and the size of soil aggregates. Changes in soil carbon stocks were mainly driven by changes in organic carbon associated with macroaggregates. For macroaggregates, PP microplastics decreased soil organic carbon (SOC) as well as dissolved organic carbon (DOC). These changes were reversed in microaggregates and silt and clay. Interestingly, PLA increased the SOC, DOC and CO2 emissions in bulk soil and all three aggregates with a dose-effect response. These changes were associated with soil microbes, functional genes and enzymes associated with the degradation of labile and recalcitrant carbon fractions. Furthermore, PP and PLA reduced bacterial community diversities and shifted bacterial community structures in both the three aggregates and in bulk soil. Alterations of functional genes induced by microplastics were the key driving factors of their impacts on carbon transformation in soil aggregates. This research opened up a new insight into the mechanisms underlying the impacts of microplastics on soil carbon transformation, and helped us make rational assessments of the risks and the disturbances of microplastics on soil carbon cycling.

Effects of woodchip biochar on temperature sensitivity of greenhouse gas emissions in amended soils within a mountain vineyard

The utilization of biochar as a soil amendment holds promise for long-term carbon sequestration due to its elevated carbon content and persistent chemical structure. This characteristic has positioned biochar as a proposed nature-based solution for climate change mitigation. Nevertheless, the impact of biochar on soil greenhouse gas (GHG) emissions remains a subject of ongoing debate. In the present investigation, we evaluated the influence of conifer wood biochar on the fluxes of three GHGs, namely carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4), in a vineyard soil subjected to biochar-alone treatments (at rates of 25 and 50 t ha−1) and in combination with green waste compost (at a rate of 45 t ha−1). The experimental field was situated in northern Italy and was organized in a randomized block design. Soil GHG fluxes were monitored for two and a half years. Monthly flux measurements were conducted using a high-resolution multi-gas analyzer for 24 hours. Fluxes were, therefore, correlated with soil temperature to assess the influence of treatments on the sensitivity of GHG emissions to this pivotal environmental parameter. The findings demonstrated diminished temperature sensitivity in the initial experimental year across all GHG fluxes in soils amended with biochar and biochar-compost combination, in contrast to treatments lacking biochar (i.e., control and compost-alone treatments). Notably, the attenuation was most pronounced for N2O emissions, suggesting a potential role of biochar in mitigating the release of this gas. However, this effect did not persist in the second and third years of the experiment. Overall, biochar significantly contributed to a reduction in N2O fluxes and an increase in CO2 fluxes, but the effect was limited and temporary. Furthermore, biochar had no impact on CH4 fluxes. The discerned fluctuation in the impact of biochar over time can be attributed to the processes of biochar aging and/or the interannual variability in soil moisture.

The impacts of film mulching and ridging on N2O emissions, relevant functional genes, and microbial communities in rain-fed potato fields

Rain-fed potato (Solanum tuberosum) fields in drylands significantly contribute to nitrous oxide (N2O) emissions, making them an important focus of agricultural greenhouse gas research. Film mulching and ridging are key agricultural methods in potato cultivation. Investigating the impact of these methods on N2O emissions, nitrifying/denitrifying functional genes, and microbial communities can provide a theoretical basis for soil emission reduction and more sustainable dryland agriculture. We examine the effects of flat tillage with mulching, ridge tillage with mulching, flat tillage without mulching, and ridge tillage without mulching, on potato fields under natural rainfall conditions in Wuchuan County, China. N2O emission fluxes were monitored using a static (dark) chamber and gas chromatography. Real-time quantitative PCR (q-PCR) was used to quantify abundances of nitrifying and denitrifying bacteria related to N2O emissions at various potato-growth stages. Illumina high-throughput sequencing was used to investigate microbial community structure by targeting 16S rRNA genes; related soil elements (soil temperatures and moisture) are analyzed. Mulching and ridging indirectly influence N2O emissions, nitrifying/denitrifying functional gene copy numbers, and microbial community structure by altering soil temperature and moisture. Cumulative N2O emissions and emission intensity were both consistently higher in ridge tillage with mulching during the potato-growing period. Ammonia-oxidizing archaea are the main microorganisms that control N2O emissions, with nitrification-coupled denitrification also being an important mechanism contributing to high N2O emissions during soil dry–wet cycles. Increased soil temperature and moisture elevated N2O emissions and functional gene copy numbers. The combination of mulching and ridging effectively uses the characteristics of both practices, making Nitrospira the dominant genus, and significantly increases N2O emissions.

The emission of CO from tropical rainforest soils

Abstract. Soil carbon monoxide (CO) fluxes represent a net balance between biological soil CO uptake and abiotic soil and (senescent) plant CO production. Studies largely from temperate and boreal forests indicate that soils serve as a net sink for CO, but uncertainty remains about the role of tropical rainforest soils to date. Here we report the first direct measurements of soil CO fluxes in a tropical rainforest and compare them with estimates of net ecosystem CO fluxes derived from accumulation of CO at night under stable atmospheric conditions. Furthermore, we used laboratory experiments to demonstrate the importance of temperature on net soil CO fluxes. Net soil surface CO fluxes ranged from −0.19 to 3.36 nmol m−2 s−1, averaging ∼1 nmol CO m−2 s−1. Fluxes varied with season and topographic location, with the highest fluxes measured in the dry season in a seasonally inundated valley. Ecosystem CO fluxes estimated from nocturnal canopy air profiles, which showed CO mixing ratios that consistently decreased with height, ranged between 0.3 and 2.0 nmol CO m−2 s−1. A canopy layer budget method, using the nocturnal increase in CO, estimated similar flux magnitudes (1.1 to 2.3 nmol CO m−2 s−1). In the wet season, a greater valley ecosystem CO production was observed in comparison to measured soil valley CO fluxes, suggesting a contribution of the valley stream to overall CO emissions. Laboratory incubations demonstrated a clear increase in CO production with temperature that was also observed in field fluxes, though high correlations between soil temperature and moisture limit our ability to interpret the field relationship. At a common temperature (25 °C), expected plateau and valley senescent-leaf CO production was small (0.012 and 0.002 nmol CO m−2 s−1) in comparison to expected soil material CO emissions (∼ 0.9 nmol CO m−2 s−1). Based on our field and laboratory observations, we expect that tropical rainforest ecosystems are a net source of CO, with thermal-degradation-induced soil emissions likely being the main contributor to ecosystem CO emissions. Extrapolating our first observation-based tropical rainforest soil emission estimate of ∼ 1 nmol m−2 s−1, global tropical rainforest soil emissions of ∼ 16.0 Tg CO yr−1 are estimated. Nevertheless, total ecosystem CO emissions might be higher, since valley streams and inundated areas might represent local CO emission hot spots. To further improve tropical forest ecosystem CO emission estimates, more in situ tropical forest soil and ecosystem CO flux measurements are essential.

A vakondjáratok hatása az extenzív gyep talajfaktor mutatóira

We investigated the effects of mole walks in extensive grassland soil, focusing on changes in soil factor indicators, 3-3 times per year, in 2022-2023, in Karcag. Based on our results, we found that the drier year 2022 had verifiably higher carbon emission values, only on an annual average, than the wetter year 2023. We found no verifiable differences in soil temperature and soil moisture conditions. Based on our data, it can be concluded that the mammal of choice for the year 2023, the mole, does not have a significant impact on the carbon dioxide emissions of the grassland soil. Further studies in other habitat conditions are definitely warranted.

Effectiveness of the Sustainable Manure Pile Model for Ammonia Emission and Soil

In order to reduce odor emissions and surface water pollution while storing manure in field heaps near a barn, there is a challenge in properly designing manure-storage areas. Therefore, it is important to assess what solutions and conditions, considering environmental requirements, should be considered when storing manure in field heaps. The goal of the research is to determine the impact of various factors on the risk of nutrient leaching, soil, and gas emissions from solid manure heaps, considering climatic factors in the environment. Through various scientific studies, a manure pile model has been developed and evaluated for its impact on the risk of potential leaching and odor emissions (using hyperspectral gas emission analysis mass flow method) from manure and the dynamics of the 0–80 cm soil layer properties (nitrate (N-NO3) and nitrite (N-NO2), ammonia (NH3), mineral, and total N). Based on the research results, requirements for manure management and storage during the prohibited fertilization period were established, considering the requirements for nitrates from agricultural sources in Lithuania. An optimal new manure heap model has been identified—a layer of not less than 20 cm of compacted straw (density 150–200 kg m−3) or a 10 cm layer of peat for absorbing manure slurries is formed on the soil surface, the manure heap is surrounded by an earth embankment not less than 30 cm high, the manure heap is covered with a layer of finely chopped straw not less than 10 cm thick, or 5 cm of sawdust, or 5 cm of peat. The manure is stored in the heap for 6–12 months. Following the research results, requirements for manure management and storage during the prohibited fertilization period were established, considering the requirements for nitrates from agricultural sources in Lithuania, applicable to the northern part of the temperate climate zone and applying similar requirements to the relevant countries.

Effects of Straw Return and Nitrogen Application Rates on Soil Ammonia Volatilization and Yield of Winter Wheat

This study investigates the impact of corn straw return and nitrogen application rates on ammonia volatilization and yield enhancement under field conditions, in order to reduce emissions while increasing crop yield. During the winter wheat season, a fissure area design was implemented, comprising three levels of straw return in the main area and three distinct nitrogen fertilizer levels in the subsidiary area, for a total of nine treatments. The results can be summarized as follows: (1) The ammonia emissions flux initially increased followed by a decrease, and was primarily concentrated within the first 14 days after fertilization, with a peak observed at 4–5 days before decreasing. Notably, nitrogen fertilizer significantly affected the cumulative ammonia emissions, ranging from 0.019 to 1.786 kg·hm−2·d−1 and 0.013 to 1.693 kg·hm−2·d−1 across the two seasons. (2) The soil with a higher nitrogen application rate exhibited elevated levels of inorganic nitrogen content and urease activity under the same straw return level. Maintaining a consistent nitrogen application level, the return of straw to the field increased the cumulative ammonia discharge, inorganic nitrogen content, and urease activity. (3) The interaction between straw return and nitrogen fertilizer substantially affected crop yield. Specifically, during the winter wheat season, the optimal combination for reducing ammonia emissions and enhancing yield was observed under straw return (both half or full) combined with 180 kg·hm−2 nitrogen application. Notably, the reduction of soil emissions and winter wheat yield augmentation were feasible through appropriate corn straw return in the preceding season.

Gypsum and structure lime amendments in boreal agricultural clay soils: Do climate emissions compromise water quality benefits?

We examine cost-effectiveness and social net benefits of using soil amendments, gypsum and structure lime, in reducing phosphorus loading while accounting for the climate emissions from both amendments. Recent field experiments and large-scale pilots in Finland and Sweden suggest that both gypsum and structure lime improve soil structure and can reduce total P loading from clayey fields but differ as soil amendments. While gypsum does not change soil pH, structure lime helps to adjust it to a desired level. Drawing on literature, gypsum is postulated to reduce both dissolved (25%) and particulate losses (50%) of phosphorus, while structure lime is postulated to reduce only particulate phosphorus (40%). Life-cycle analysis is applied to determine greenhouse gas emissions from both soil amendments. We examine 5 and 10 years impacts on phosphorus loss by choosing doses and their timing accordingly. Both amendments provide the highest water quality benefits on erodible soils or soils with high soil phosphorus. Accounting for climate issues drastically changes the picture. Greenhouse gas emissions from gypsum production are 14.43 kgCO2e ha-1, and those from structure lime from pristine materials are 1837 kgCO2e ha-1. Cost-effectiveness of P load reduction including carbon price of GHG emissions is 59 € kg-1P for gypsum and 122 € kg-1P for structure lime. At the national level (application to 0.54 Mha), differences in greenhouse gas emissions without soil emissions are huge and in favour of gypsum (0.048 Mt and 1.04 Mt). Structure lime from recycled zero-emission materials performs well but its supply is very limited.

Interactive effects of soil salinity and nitrogen fertilizer types on nitrous oxide and ammonia fluxes

Soil salinization, impaired by climate change and poor management practices, poses a global threat, particularly in arid and semi-arid regions, leading to significant land degradation. This study aims to investigate the effects of different nitrogen (N) fertilizer sources (urea, ammonium-sulfate, and biogas waste) on CO2, N2O, and NH3 emissions and soil enzyme activities in two soil types varying in salinity level (non-saline: EC = 1.15 dS m−1, and saline: EC = 35.80 dS m−1) in a robotized continuous-flow soil incubation system. Our results showed a sharp increase in N2O and CO2 emissions (up to 0.51 ± 0.02 g N2O-N ha−1 day−1, 28.1 ± 3.9 kg CO2-C ha−1 day−1) in non-saline soils following soil rewetting, attributed to bacterial denitrification. However, this pattern was not observed in saline soils, suggesting that salinity causes partial inhibition to the regeneration of soil organic matter mineralization and denitrification processes after rewetting. Although salinity did not alter the overall cumulative N2O losses in any fertilizer treatment, it significantly delayed the evolution of N2O peak during the incubation period. On the other hand, NH3 volatilization was significantly higher in N-fertilized saline soils compared to non-saline soils (241% and 157% in ammonium-sulfate and biogas waste treatments, respectively), except for urea treatment, likely due to the decrease in nitrification rates. Furthermore, the study clearly showed lower soil enzyme activity levels for both nitrate reductase and urease activity. Interestingly, the lowest NH3 emissions were measured in urea treatment in both soils. Overall, our findings highlight the complex interplay between soil salinity, nitrogen fertilizer sources, and microbial processes, significantly influencing gaseous nitrogen emissions and N cycling in agricultural soils. Identifying the specific fertilizer treatments that minimize or maximize gaseous nitrogen losses in varying soil salinity, may guide the selection of appropriate fertilization strategies for farmers and policymakers to mitigate environmental impacts of fertilizer use during agricultural production.

Synchronous influence of soil amendments on alkylmercury and methane emissions in mercury-contaminated paddy soil

Mercury (Hg) alkylation and methane (CH4) emissions pose significant global concerns. Paddy soil, due to its long-term anaerobic conditions and abundant organic matter, is hotspots for soil Hg alkylation and CH4 emissions. However, the relevance between Hg alkylation and CH4 emissions, especially their simultaneous reduction strategies, remains poorly understood. Here, we investigated the effects of biochar (BC), selenium (Se) and rice straw (RS) amendments on Hg alkylation and CH4 emissions in paddy soil, and the accumulation of Hg speciation. Results found that both BC and RS amendments significantly increased the levels of soil organic carbon (SOC) and humification index (HIX). Furthermore, BC decreased the concentrations of Hg(II), methylmercury (MeHg) and ethylmercury (EtHg) by 63.1%, 53.6% and 100% in rice grains. However, RS increased Hg(II) concentration but decreased the total Hg (THg), MeHg and EtHg concentrations in rice grains. Compared to the CK, RS significantly increased CH4 emissions, while BC decreased CH4 emissions, and Se showed no significant difference. Se amendment increased the Hg(II) and EtHg concentrations by 20.3% and 17.0% respectively, and decreased the MeHg concentration in grains by 58.3%. Both BC and RS impacted the abundance of methanogens by enhancing SOC and HIX, subsequently modulating the relevance between Hg alkylation and CH4 emissions. These findings provide insights into the relevance between Hg alkylation and CH4 emissions and propose potential mitigation mechanisms in Hg-contaminated paddy soil.

Changes in source composition of wet nitrate deposition after air pollution control in a typical area of Southeast China

In recent years, China has adopted numerous policies and regulations to control NOx emissions to further alleviate the adverse impacts of NO3−-N deposition. However, the variation in wet NO3−-N deposition under such policies is not clear. In this study, the southeastern area, with highly developed industries and traditional agriculture, was selected to explore the variation in NO3−-N deposition and its sources changes after such air pollution control through field observation and isotope tracing. Results showed that the annual mean concentrations of NO3−-N in precipitation were 0.67 mg L−1 and 0.54 mg L−1 in 2014–2015 and 2021–2022, respectively. The average wet NO3−-N depositions in 2014–2015 and 2021–2022 was 7.76 kg N ha−1 yr−1 and 5.03 kg N ha−1 yr−1, respectively, indicating a 35% decrease. The δ15N–NO3− and δ18O–NO3− values were lower in warm seasons and higher in cold seasons, and both showed a lower trend in 2021–2022 compared with 2014–2015. The Bayesian model results showed that the NOx emitted from coal-powered plants contributed 53.6% to wet NO3−-N deposition, followed by vehicle exhaust (22.9%), other sources (17.1%), and soil emissions (6.4%) during 2014–2015. However, the contribution of vehicle exhaust (33.3%) overpassed the coal combustion (32.3%) and followed by other sources (25.4%) and soil emissions (9.0%) in 2021–2022. Apart from the control of air pollution, meteorological factors such as temperature, precipitation, and solar radiation are closely related to the changes in atmospheric N transformation and deposition. The results suggest phased achievements in air pollution control and that more attention should be paid to the control of motor vehicle exhaust pollution in the future, at the same time maintaining current actions and supervision of coal-powered plants.

Substantial contribution of inorganic carbon sources to CO2 emissions in calcareous vineyard soils in Germany

AbstractIn light of climate change and increasing global temperatures, it is important to equally prioritize the study of inorganic carbon dynamics in calcareous soils within temperate ecosystems, as has been done for arid or semiarid environments. A significant area of vineyards in Germany is established on calcareous soils. However, the potential influence of inorganic carbon on CO2 emissions in these vineyards has not been sufficiently explored when evaluating the carbon footprint of management practices in relation to carbon storage. Therefore, we aimed to differentiate between organic and inorganic sources of CO2 emissions from six vineyard soils located in the southwest of Germany that had previously received organic soil amendments (OA). Inorganic carbon content varied between 8 and 55 g kg−1 across different sites, with variations observed in the inorganic‐to‐organic carbon ratio. Soil samples were incubated under standard laboratory conditions for 48 h, and the source of emitted CO2 was determined using a two‐end‐member mixing model. The contribution of inorganic carbon to CO2 emissions was influenced by the quantity of inorganic carbon, with an increase in contribution with increasing inorganic‐to‐organic carbon ratio. On average, abiotic sources accounted for 5% to 40% of the emitted CO2 at the different sites, with one site showing no significant contribution of inorganic carbon. CO2 production from inorganic carbon was higher in the subsoil compared with the topsoil, likely related to the higher content of inorganic carbon in the subsoil. Notably, there was no discernible influence of OA on carbonate dissolution. This study emphasizes the significance of considering abiotic sources of CO2 emissions in addition to soil respiration in calcareous soils and highlights the need for further investigation to apply these findings at the field scale.

Copper contribution to rice production and greenhouse gas emissions in hydrophobic peat soil

Abstract Harnessing the potential of hydrophobic peat for rice cultivation through effective amelioration and fertilization such as the application of copper (Cu) fertilizer. A greenhouse experiment was conducted, employing a treatment of Cu fertilizer at a rate of 5 kg/ha. The objective of this study was to determine the contribution of Cu in rice production and influencing of greenhouse gas emissions. N P K fertilizers were applied as basal fertilizers according to the recommended dosage for rice crops. The research findings revealed that the application of Cu fertilizer increased the dry grain weight per tiller by 14.2%. This application also resulted in higher soil pH and increased Cu concentrations in plant tissue above critical levels. The study also showed that the Cu application contributed to the increased concentrations of CO2 and CH4, although these differences were not statistically significant when compared to treatments without Cu application. The study implies that copper (Cu) is an essential micronutrient crucial for the growth and development of rice plants, especially in hydrophobic peat soil.

Impact of nitrapyrin on urea‐based fertilizers in a Mediterranean calcareous soil: Nitrogen and microbial dynamics

AbstractNitrification inhibitors, such as nitrapyrin (NI), are increasingly co‐applied with nitrogen (N) fertilizers as part of sustainable agricultural practice. Several studies in temperate regions have documented the effectiveness of NI in retaining soil ammonium (NH4+), minimizing N loss and increasing crop yields. However, less is known about the effects of NI in Mediterranean regions, where agricultural production is challenging and requires intensive irrigation and fertilization. We investigated the short‐term impact of the nitrification inhibitor nitrapyrin (2‐chloro‐6‐(trichloromethyl)pyridine) in a two‐factor mesocosm experiment, using a typical Mediterranean soil, where NI was co‐applied with a selection of urea‐based fertilizers: urea (U), U with urease inhibitors (U + UI), methylene urea (MU) and zeolite‐coated urea (ZU). NI co‐applied with urea fertilizers resulted in higher availability of soil NH4+ and a concurrent increase in NH3 volatilization. Net cumulative soil NH4+ availability was 1.5–3.3 fold greater when NI was applied. Concurrently, net cumulative nitrate (NO3−) and nitrite (NO2−) availability was reduced by 10%–60%; this was found for all the tested fertilizer types except MU fertilizer, where the net cumulative soil NO3− and NO2− doubled. Nitrous oxide (N2O) emissions from urea fertilization were reduced by 40% with UI, 50% with NI and 66% with NI + UI. Interestingly, after 28 d, the composition of soil microbial communities was distinctly different, due to NI application. Specifically, NI application dramatically reduced the abundance of ammonia‐oxidizing and denitrifying bacterial functional groups. NI was effective in reducing N2O emissions in this calcareous soil; however, NH3 emissions were remarkably enhanced. These findings have important implications for the large‐scale adoption of inhibitor technologies in Mediterranean agroecosystems and for the reduction of greenhouse gas emissions.

Greenhouse gas emissions from sandy soils amended with lime and gypsum under different initial soil pH and nitrogen sources

AbstractLime (CaCO3) application has led to an inconsistent mitigation of greenhouse gas emissions (GHGs) from agricultural soils. In addition, only a few studies have investigated the impact of gypsum (CaSO4) on the release of GHGs. Therefore, here we investigated the impact of initial soil pH and nitrogen sources on CaSO4 and CaCO3 effectiveness in reducing the production of GHGs. We hypothesized that (i) liming presents the highest effectiveness in reducing GHGs when performed in acidic soil and under NO3−‐N fertilizer application, and (ii) application of CaSO4 is not effective in reducing GHG irrespective of the initial soil pH or nitrogen (N) source. Firstly, an incubation experiment was carried out to evaluate the effect of initial soil pH using acidic soil and neutral soil amended with CaSO4 and CaCO3. Subsequently, a second incubation experiment was conducted to investigate the effect of N source by applying calcium nitrate and urea in an acidic soil amended with CaSO4, CaCO3 and CaSO4 + CaCO3. The measured variables were soil , daily and cumulative emissions of N2O‐N, CO2‐C and CH4‐C, as well as NH4+‐N and NO3−‐N concentrations. CaCO3 did not affect N2O‐N emission under neutral soil pH, and NO3−‐N fertilizer application. However, CaCO3 increased N2O‐N release under acidic soil (+96%), and urea fertilizer application (+97%). Furthermore, CaCO3 and CaSO4 reduced CO2‐C emission from the neutral pH soil by 31%, and CaSO4 decreased the mean cumulative N2O‐N release from the soil fertilized with urea‐N by 43%. In conclusion, this study did not confirm liming as an alternative to reduce N2O‐N release under different initial soil pH and N sources. Furthermore, our results indicated that CaSO4 may decrease GHG emissions. Finally, these results suggest caution for considering liming as a strategy to mitigate N2O‐N emission from agriculture.