Soil Carbon Changes Research Articles

Soil nitrogen and carbon changes in a biosolid amended sodic vertisol with a history of treated sewage effluent‐enriched water irrigation

AbstractThe application of biosolids to cropping soils may improve soil health, supply nitrogen and other nutrients for crops. There are specific guidelines on the quantity of biosolids that can be applied to a soil to grow selected crops. However, some recommendations overlook environmental factors such as soil organic N and N supplied by irrigation water. We conducted a three‐year field monitoring programme to study the effect of biosolid application on sodicity, soil nitrogen and organic carbon status to a depth of 1.8 m in a vertisol with a history of sewage effluent water irrigation. Biosolid application had no effect on soil sodicity. Improvements in soil organic carbon (SOC) were short‐lived and occurred only during the first year. N accumulation and leaching below the root zone (1.2 m) occurred after two years and suggest a possible off‐farm environmental risk. The higher residual mineral N in biosolid treatment 2 years after application implies an opportunity to reduce N inputs in vertisols treated with biosolids and effluent water. The biosolid application rate of 35 Mg ha−1 was well below the nitrogen‐limited biosolid application rate (NLBAR) (100 Mg ha−1) under the current guidelines. This warrants further refinement of NLBAR to suit specific circumstances such as effluent‐enriched water irrigation and additional in‐crop fertilizer application.

Exploring the likely relationship between soil carbon change and environmental controls using nonrevisited temporal data sets: Mapping soil carbon dynamics across China

The prediction of soil organic carbon (SOC) changes in response to environmental change is often limited by a scarcity of revisited temporal data, which constrains scientific understanding and realistic predictions of soil carbon change. The present study improved the potential of nonrevisited temporal data in the prediction of SOC stocks (SOCS) variations. We proposed a method to develop predictions of SOCS change using two independent temporal data sets (pertaining to the 1980s and 2010s) in China based on the digital soil mapping technique. Changes in SOCS over time at the site level were analyzed via the interpolation of missing SOCS values in each data set. Quantitative SOCS change predictions were generated by modeling the relationship between SOCS change and variables that represent changes in climate, vegetation indices, and land cover. The scale-dependent response of SOCS change to these environmental dynamics was assessed. On average, a slight increase was observed from 3.70 kg m−2 in the 1980s to 4.53 kg m−2 in the 2010s. The proposed approach attained moderate accuracy with an R2 value of 0.32 and a root mean squared error (RMSE) of 1.73 kg m−2. We found that changes in climate factors were dominant controls of SOCS change over time at the country scale. At the regional scale, the controlling factors of SOCS change were distinct and variable. Our case study may be of value in the application of independent temporal data sets to analyze soil carbon change on multiple scales. The method may be used to resolve questions of soil carbon change projections and provide an alternative solution to predict likely changes in soil carbon in response to future environmental change when no temporal data are available.

Simulation of soil carbon changes due to conventional systems in the semi-arid region of Brazil: adaptation and validation of the century model

Soils play an important role on the global carbon cycle, but conventional land use practices generate negative impact by reducing soil organic carbon (SOC) content. Studies regarding the use of mathematical models on the magnitude of such impacts are scarce in semi-arid regions, but they are essential to broaden the understanding of the effects of cropping systems and help in proposing more rational land use alternatives. However, mathematical models (e.g. Century) must be previously calibrated and validated to present satisfactory results. Therefore, the aim of the present study was to validate the Century model for simulating SOC dynamics in areas of native vegetation and estimating SOC stocks on the adoption of agricultural systems in the semi-arid region of Brazil with a previous calibrated model. The study was carried out in three soil types (Quartzipsamments, Psamments and Ultisol), located in the state of Alagoas, north-eastern Brazil, adopting conventional (with minimal use of machinery) agricultural land-use practices under rainfed conditions. Simulations consisted of validating the model with previously calibrated parameters from another area of the Brazilian semi-arid region. The results showed that the model proved to be effective in simulating SOC dynamics in areas of native vegetation in the semi-arid region of Alagoas (PBIAS ranging from 20 to −9%); however, it needs further adjustment for satisfactory SOC simulation in agricultural/pasture systems. The results showed that conventional systems of agricultural crops and pasture in the semi-arid region of Brazil lead to losses (2673 g C m −2 in native vegetation to 1960 g C m −2 in conventional systems) between 22% and 35%, (PBIAS variating −9 to 49%) and that SOC stocks reach a new steady state between 30 and 40 years after conversion from native vegetation into agriculture (ranging from 24 to 42% in different soil types).

Dynamics of ecosystem carbon stocks in a chronosequence of nitrogen‐fixing Nepalese alder (Alnus nepalensis D. Don.) forest stands in the central Himalayas

AbstractNitrogen‐fixing Nepalese alder (Alnus nepalensis D. Don.) is a rapidly‐growing pioneer tree species that often forms pure stands in areas affected by landslides, but also occurs mixed with other late‐successional species in the central Himalayas. In this study, we assessed the distribution of carbon in vegetation and soil in a chronosequence of A. nepalensis (3–270 years old) forest stands and evaluated its correlation with the stand and alder total basal area (TBA). The study was conducted in six different naturally occurring forest stands in a chronosequence, viz., alder‐early regenerating (AER), alder‐late regenerating (ALR), alder young‐mixed (AYM), alder mature‐oak (Quercus leucotrichophora) mixed (AMOM), alder mature‐rhododendron (Rhododendron arboreum) mixed (AMR), and alder old‐oak (Q. leucotrichophora) mixed (AOOM) forests. The chronosequence consisted of three young unreserved, AER, ALR, and AYM (age 3–25) and three older reserved, AMOM, AMR, and AOOM (age 80–270) stands. We used structural equation modelling (SEM) to quantify the contribution of various carbon pools on ecosystem carbon stock. Forest carbon stock significantly increased (p < 0.05) with forest age and TBA, indicating that succession is the driving factor of the forest ecosystem processes, carbon accumulation, and therefore, change in vegetation biomass carbon and soil carbon in the chronosequence of A. nepalensis forests. Total vegetation biomass carbon (tree, shrubs, herbs, and litter) contained ~12.54–289.85 Mg ha−1 (79.11–57.77% total carbon stock), and soil carbon (depths of 0–10 cm in AER, 0–30 cm in AYM, 0–100 cm in remaining forest stands) contained ~3.31–210.13 Mg ha−1 (20.8–42% total carbon stock) and positively increased with stand and A. nepalensis TBA. The tree layer biomass carbon stock was considerably higher than the understory (shrubs, herbs, and forest floor). The soil carbon stock was reported to be influenced by the successional stages. Therefore, these findings reflect that the A. nepalensis forest development in the central Himalayas lead to storage of large amount of carbon stock in both plant biomass and soil.

Reindeer control over subarctic treeline alters soil fungal communities with potential consequences for soil carbon storage.

The climate-driven encroachment of shrubs into the Arctic is accompanied by shifts in soil fungal communities that could contribute to a net release of carbon from tundra soils. At the same time, arctic grazers are known to prevent the establishment of deciduous shrubs and, under certain conditions, promote the dominance of evergreen shrubs. As these different vegetation types associate with contrasting fungal communities, the belowground consequences of climate change could vary among grazing regimes. Yet, at present, the impact of grazing on soil fungal communities and their links to soil carbon have remained speculative. Here we tested how soil fungal community composition, diversity and function depend on tree vicinity and long-term reindeer grazing regime and assessed how the fungal communities relate to organic soil carbon stocks in an alpine treeline ecotone in Northern Scandinavia. We determined soil carbon stocks and characterized soil fungal communities directly underneath and >3m away from mountain birches (Betula pubescens ssp. czerepanovii) in two adjacent 55-year-old grazing regimes with or without summer grazing by reindeer (Rangifer tarandus). We show that the area exposed to year-round grazing dominated by evergreen dwarf shrubs had higher soil C:N ratio, higher fungal abundance and lower fungal diversity compared with the area with only winter grazing and higher abundance of mountain birch. Although soil carbon stocks did not differ between the grazing regimes, stocks were positively associated with root-associated ascomycetes, typical to the year-round grazing regime, and negatively associated with free-living saprotrophs, typical to the winter grazing regime. These findings suggest that when grazers promote dominance of evergreen dwarf shrubs, they induce shifts in soil fungal communities that increase soil carbon sequestration in the long term. Thus, to predict climate-driven changes in soil carbon, grazer-induced shifts in vegetation and soil fungal communities need to be accounted for.

Can Agricultural Management Induced Changes in Soil Organic Carbon Be Detected Using Mid-Infrared Spectroscopy?

A major limitation to building credible soil carbon sequestration programs is the cost of measuring soil carbon change. Diffuse reflectance spectroscopy (DRS) is considered a viable low-cost alternative to traditional laboratory analysis of soil organic carbon (SOC). While numerous studies have shown that DRS can produce accurate and precise estimates of SOC across landscapes, whether DRS can detect subtle management induced changes in SOC at a given site has not been resolved. Here, we leverage archived soil samples from seven long-term research trials in the U.S. to test this question using mid infrared (MIR) spectroscopy coupled with the USDA-NRCS Kellogg Soil Survey Laboratory MIR spectral library. Overall, MIR-based estimates of SOC%, with samples scanned on a secondary instrument, were excellent with the root mean square error ranging from 0.10 to 0.33% across the seven sites. In all but two instances, the same statistically significant (p < 0.10) management effect was found using both the lab-based SOC% and MIR estimated SOC% data. Despite some additional uncertainty, primarily in the form of bias, these results suggest that large existing MIR spectral libraries can be operationalized in other laboratories for successful carbon monitoring.

Deforestation and land use change mediate soil carbon changes in the eastern Brazilian Amazon

Deforestation and land use change mediate soil carbon changes in the eastern Brazilian Amazon

Animal waste use and implications to agricultural greenhouse gas emissions in the United States

The increasing production of manure is a challenge for livestock management systems as well as the global environment. Being traditionally, and still dominantly, used as fertilizers, land application of manure could preserve soil fertility and improve soil carbon sequestration. However, manure application also increases nitrous oxide (N2O) emissions that might outweigh the benefits of carbon gains. Here we quantify soil carbon change and greenhouse gas (GHG) emissions from corn production systems in the United States from a life-cycle perspective. We show that utilizing manure can reduce mineral fertilizers use, and therefore avoid GHG emissions that would otherwise occur due to mineral fertilizer production and application. As a result, corn produced under manure has a reduced intensity of GHG emissions (1.5 t CO2e ha−1 or 0.15 t CO2e t−1 corn grain), about 15% less than those under sole mineral fertilizers. Owing to a sizeable amount of avoided emissions counterbalancing N2O, the soil carbon gain derived from manure use can largely contribute to net climate change mitigation. It should be noted that GHG emissions estimation can be largely improved as more robust and recent data become available to better represent spatially specific land management and to integrate ecosystem models with life-cycle model. Future studies are merited to further assess the alternative fate of manure, and expand the system boundary to assess agriculture and livestock sectors holistically.

Changes in soil carbon and nutrients and related extracellular enzymes in successive rotations of Japanese larch plantations

Extensive areas of secondary forests (SF) have been converted into larch plantations to meet the demand for timber and other forest products in northeast China since the early 1960s. However, the successive rotations of larch plantations may alter the understory vegetation and soil properties following reforestation. The aim of this study was to determine how soil carbon and nutrients and related extracellular enzymes changed after conversion from SF to larch plantations. Six larch plantations, including 16-, 30- and 47-year-old in the first rotation, 8-, 16-, and 30-year-old in the second rotation, and one adjacent SF as the 0-year site were selected using the space-for-time substitution (chronosequence) method. The results showed that most soil parameters [pH, soil organic carbon (SOC), total nitrogen (TN), available nitrogen (AN) and available potassium (AK) concentrations, and β-glucosidase, N-acetyl-glucosamine, cellobiohydrolase, and phenol oxidase activities] decreased initially from 16- to 30-year-old in the first rotation, and then increased from 30- to 47-year-old in the first rotation and 8-year-old in the second rotation, and were finally reduced from 8- to 30-year-old in the second rotation after conversion from SF, whereas soil bulk density (SBD) showed the inverse pattern. However, SOC (except at 0–10 cm) and nutrient stocks did not change significantly along the chronosequence. Redundancy analysis showed that litter biomass significantly affected most of the soil parameters, and correlated significantly and negatively with the concentrations of SOC, TN, AN and AK, and the activities of β-glucosidase, N-acetyl-glucosamine, cellobiohydrolase and phenol oxidase, while it had a significant positive relationship with SBD. Thus, rational thinning treatments should be conducted at earlier 16 years to create available space and favorable conditions for understory vegetation and litter decomposition. The appropriate rotation age of a larch plantation should be > 45 years with effective measures to maintain soil sustainability.

Effects of Semiarid Wheat Agriculture Management Practices on Soil Microbial Properties: A Review

Agricultural management decisions on factors such as tillage, fertilization, and cropping system determine the fate of much of the world’s soils, and soil microbes both mediate and respond to these changes. However, relationships between management practices and soil microbial properties are poorly understood, especially in semiarid regions. To address this knowledge gap, we reviewed research papers published between 2000 and 2020 that analyzed soil microorganisms in semiarid wheat fields. We aimed to determine if and how soil microbial properties reliably respond to management, and how these properties indicate long-term changes in soil health, carbon (C) sequestration, and crop yield. We found that reducing tillage increases microbial activity as much as 50% in upper soil layers and stratifies both bacteria and fungi by depth. Higher cropping intensity (reduced fallow) increases C storage, microbial activity, and biomass, and particularly fungal biomass, which can be three times greater under continuous wheat than wheat-fallow. Chemical and organic fertilizers both increase bacterial biomass, though only organic inputs provide lasting benefits by promoting C storage and increasing fungal as well as bacterial biomass. We found microbial properties to be sensitive indicators of long-term changes in soil health and productivity, and formed recommendations on appropriate sampling, analysis, and interpretation of microbial data depending on the system studied.

Carbon and nitrogen stocks and microbiological attributes of soil under eucalyptus cultivation in the Pampa biome of southern Brazil

In the south of Brazil, the intensification of eucalyptus planting can impact the local biome, characterized by grasslands that extends to Uruguay and Argentina. Thus, the objective of the study was to evaluate changes in soil carbon, nitrogen and their labile fractions and soil microbiological attributes due to the introduction of eucalyptus cultivation in the Pampa biome. The soils evaluated were Eutric Regosol (RG), Haplic Lixisol (LX), Dystric Leptosol (LP) and Pellic Vertisol (VR). For this, areas of homogeneous cultivation of Eucalyptus saligna (7 years old) and areas of grassland (native vegetation) were selected. Physical granulometric fractionation of soil organic matter (SOM) was performed in the 0–5, 5–10 and 10–15 cm soil layers, quantifying levels, stocks and distribution of total organic carbon (TOC) and total nitrogen (TN) in the labile and associated with minerals fractions, and the carbon management index (CMI) was calculated. In the 0–5 and 5–10 cm soil layers, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), basal soil respiration, metabolic coefficient, MBC / TOC, MBN / TN, MBC / MBN ratios were also evaluated. Eucalyptus cultivation increased the TOC and POC carbon stocks by 8.7 and 21.7%, respectively (0-15 cm) in compared to grassland. It was also observed that the cultivation of eucalyptus increased 6.7% and 26.0% the stocks of TN and PN, respectively, compared to grassland in the pampa biome. Carbon stocks associated with minerals were not affected by eucalyptus cultivation. The cultivation of eucalyptus increased the basal respiration and the microbial biomass carbon in relation to grassland and there is a reduction of microbial biomass nitrogen in the soil. Thus, the cultivation of eucalyptus in the Pampa biome in southern Brazil demonstrates that it is a forest crop that can contribute to the increase in total and labile carbon stocks and also the biomass and microbial activity of the soil, which are important indicators of assessment of soil quality.

Sustainability Assessment of Pasture-Based Dairy Sheep Systems: A Multidisciplinary and Multiscale Approach

This article describes a novel methodological approach for the integrated sustainability assessment of pasture-based dairy sheep systems. Most studies on livestock system sustainability focus on animal production, farm profitability, and mitigation strategies of greenhouse gas emissions. However, recent research indicates that pasture-based livestock farming also contributes positively to rural areas, and the associated increase in plant diversity promotes ecosystem functioning and services in natural and managed grasslands. Likewise, little attention has focused on how pasture-based livestock systems affect soil carbon changes, biodiversity, and ecotoxicity. Furthermore, the quality and safety of food products, particularly sheep milk and cheese, and socioeconomic issues such as cultural heritage and consumer behavior are often neglected in livestock system sustainability assessments. To improve the analysis of sustainability and adaptation strategies of livestock systems, we suggest a holistic approach that integrates indicators from diverse disciplines with complementary methods and models capable of capturing the complexity of these systems at multiple scales. A multidisciplinary perspective generates new indicators to identify critical trade-offs and synergies related to the resilience of dairy sheep livestock systems. A multiscale approach provides insights on the effects of socioeconomic and environmental changes associated with current dairy sheep grazing systems across multiple scales. The combined approach will facilitate the development and progressive implementation of novel management strategies needed to adapt pasture-based dairy sheep farms to changing conditions under future socioeconomic and environmental scenarios.

Changes in soil carbon, nitrogen, and phosphorus contents, storages, and stoichiometry during land degradation in jasmine croplands in subtropical China

AbstractSoil degradation is characterized by loss of soil organic matter, decline in fertility, imbalance in elemental content, deterioration of soil structure, and overall a deterioration of soil environment. According to the classification method of Pieri et al. (1992), the soil is classified into different degradation classes by calculating the soil structural stability index (St) of each sample point. We aimed to investigate changes in the contents, storages and stoichiometry of soil carbon (C), nitrogen (N), and phosphorus (P) together with changes in soil physical traits along a soil degradation gradient in jasmine croplands in Fuzhou area (China). The content and storage of soil C and N decreased with increasing intensity of land degradation. Soil organic C content was 15.4%, 32.3%, and 38.8% lower, respectively, in the low, medium, and high degree of degradation soils, than in the nondegraded soils. The soil C:N ratio was 18.5% higher in soils in the middle degree of degradation than in the nondegraded soils. Compared with nondegraded soils, the bulk density of the degraded soils increased and water content decreased. The decrease of soil pH coupled with salinity (conductivity) and the loss of aggregate stability are the main traits that distinguish degraded from nondegraded soils. We also detected a general N and P deficiency that is aggravated by the degradation process. Unreasonable management easily leads to degradation associated with a loss of organic C and total soil nutrients, thus impairing even more a general N and P deficiency in this area. Therefore, higher inputs of organic fertilizer should be added to alleviate the lack of organic matter, and appropriate burial should be conducted to reduce nutrient loss. Moreover, a rise of N and P fertilizer application is also advisable.

Changes in soil bacterial communities, and carbon and nitrogen metrics as potential indicators of land use effects in a humid tropical forest

It is unclear how different management practices influence tropical soil ecosystems in post-logging habitats over short or long terms. In this project, we demonstrated that critical differences in soil C and N metrics, organic C use efficiency, and DNA-identified bacterial community structures occurred along a land use disturbance gradient in a humid tropical primary forest (PF) Costa Rica following deforestation and conversion of the forest into logging roads (LR), grasslands that were grazed and then abandoned (GR), and regenerating secondary forests (SF). The mean proportion of DNA sequences, their richness and diversity for total bacterial genera and those linked to N-fixation, ammonium oxidation, and degradation of complex organic C compounds were generally greater in the PF than the SF soils, followed by the GR and then the LR soils. The specific land use-associated changes in soil NO3−/NH4+, TN, TOC, and biomass C/TOC best predicted these differences in bacterial communities. The SF soil ecosystems were on a better trajectory towards similarity with the PF soils, followed by the GR soils, with the LR soils still being the most negatively influenced. This study showed that the soil biotic and abiotic factors were clearly different along the disturbance gradient, with each soil ecosystem responding differently to the forest clearing, followed by development of logging roads, abandoned grasslands, and secondary forests. This work also showed that differences in C and N metrics, and the structure of total and functional group communities of bacteria, in particular, the genera Solibacter, Burkholderia, Bradyrhizobium, Comamonas, Geobacter, Azospirillum, Nitrospira, Nitrosovibrio, Rhodoplanes and Phenylobacterium can serve as future indicators of soil damage and recovery following different types of disturbances.

The temperature sensitivity of soil: microbial biodiversity, growth, and carbon mineralization.

Microorganisms drive soil carbon mineralization and changes in their activity with increased temperature could feedback to climate change. Variation in microbial biodiversity and the temperature sensitivities (Q10) of individual taxa may explain differences in the Q10 of soil respiration, a possibility not previously examined due to methodological limitations. Here, we show phylogenetic and taxonomic variation in the Q10 of growth (5-35 °C) among soil bacteria from four sites, one from each of Arctic, boreal, temperate, and tropical biomes. Differences in the temperature sensitivities of taxa and the taxonomic composition of communities determined community-assembled bacterial growth Q10, which was strongly predictive of soil respiration Q10 within and across biomes. Our results suggest community-assembled traits of microbial taxa may enable enhanced prediction of carbon cycling feedbacks to climate change in ecosystems across the globe.

Elevated CO2 shifts soil microbial communities from K‐ to r‐strategists

AbstractAimsSoil microbes are key to myriad processes in terrestrial ecosystems. Elevated CO2 represents a dominant driver of global climate change; however, it remains unclear to what extent elevated CO2 impacts soil microbial communities at ecosystem and global scales. Here, we sought to address the following questions: (a) Do the compositions of microbial communities shift from K‐ to r‐strategists under elevated CO2? (b) What is the extent of the compositional shifts of microbial communities affected by elevated CO2 concentrations, experimental duration, ecosystem types and/or background climates? (c) Are the responses of microbial communities to elevated CO2 associated with changes in soil pH and carbon and nitrogen availabilities?LocationGlobal.Time period1998–2020.Major taxa studiedSoil microbes.MethodsWe performed a global meta‐analysis of 965 observations from 122 studies, which tested the effects of elevated CO2 on microbial communities. The data covered broad variations in ecosystems, climate, CO2 concentrations, experimental duration, and soil factors.ResultsWe revealed that elevated CO2 decreased the K‐ to r‐strategist ratios with decreasing fungi : bacteria, Gram+ : Gram– bacteria, and Acidobacteria : Proteobacteria ratios, and increased bacterial biomass, microbial biomass carbon, Gram– bacteria, and Acidobacteria abundance. Moreover, the shifts from K‐ to r‐strategists were more pronounced under higher CO2 concentrations and longer experimental durations. The responses of microbial attributes to elevated CO2 did not differ significantly among croplands, forests and grasslands. Furthermore, the response of microbial biomass to elevated CO2 was negatively correlated with the response of soil pH, while those of bacterial biomass and fungi : bacteria ratios were positively correlated with those of soil organic carbon and soil carbon : nitrogen ratios, respectively.Main conclusionsOur results suggest that elevated CO2 shifts soil microbial communities from K‐ to r‐strategists, and provide supportive evidence for understanding responses of soil microbial processes to elevated CO2.

Soil Contamination Assessments from Drilling Fluids and Produced Water Using Combined Field and Laboratory Investigations: A Case Study of Arkansas, USA.

Rotary drilling for oil and natural gas uses drilling fluid for lubrication of the bit, to seal off unstable shale layers, and floating out rock cuttings. Drilling fluid is a water–clay chemical mixture. Produced water is a water–sand chemical mixture. Land farming is a common disposal technique of drilling fluid and produced water. In the land farming process, amendments of fluid are repeatedly applied to the soil surface. Plant growth and soil chemical properties may be altered by additions of drilling fluid, because of alkalinity, salinity, trace elements, and petroleum residue contained in waste. The objective of this study was to determine the change in soil pH, electrical conductivity (EC), total nitrogen and carbon, and extractable nutrient levels following the land application of drilling fluid and produced water. The study was a comparison of three plots with similar soil properties and conditions. The three study plots had various levels of drilling fluid and produced water applications. The data show a major difference from field-to-field for EC, Na, and Cl levels. The EC and salt levels increased with additional applications of drilling fluid and produced water. The percent total nitrogen values and plant available P levels were very low in all fields. High EC and salt values, coupled with low N and P levels, would be detrimental to plant growth and development. To successfully vegetate this land-farm site, application of N and P fertilizer would be required. This study help to give a better understanding of practical ways to land-farm drilling fluid and produced water in a fashion that both minimizes environmental issues and is economically feasible in Arkansas. Thus, this research will provide important information for soil contamination management and contributes on understanding of the responses of soil properties to drilling fluid and produced water in the future.

Sea-level rise enhances carbon accumulation in United States tidal wetlands

Sea-level rise enhances carbon accumulation in United States tidal wetlands

작기 중 물관리를 실시한 휴경기 논에서의 온실가스 배출 특성 조사 : 순 지구온난화지수 산정(net GWP)

Approximately 51% of the greenhouse gas (GHG) emissions generated by the agricultural sector in Korea are emitted from rice fields. Despite the extended fallow season, the calculation of GHG emissions from rice fields has been limited to rice cropping season. In this study, we sought to provide information on GHG emission considering the carbon budget in the fallow season. To compare the influence of water management during cropping season and how it affects the fallow season, two different treatments were examined, continuously flooded (CF-fallow) and intermittent drainage (ID-fallow). The emission rates of methane (CH₄), nitrous oxide (N₂O), and carbon dioxide (CO₂) were monitored using the closed chamber method. Changes in soil carbon were estimated using the net ecosystem carbon budget (NECB) method and the net global warming potential (GWP) calculated. Seasonal CH₄ and N₂O emissions were not significantly different between treatments, but the seasonal CO₂ emission for CF-fallow was significantly higher than that of ID-fallow. The net GWP was 5062 ㎏ CO₂-eq. haSUP-1/SUP for CF-fallow and 4433 ㎏ CO₂-eq. haSUP-1/SUP for ID-fallow. Approximately 77% of the calculated net GWP value was affected by the NECB value, followed by 22 ~ 23% affected by N₂O emission. In contrast, the influence of methane on net GWP was less than 1%, suggesting little effect on GHG emissions. In order to reduce GHG emissions during the fallow season in rice paddies, carbon enhancement through the input of carbon sources into the soil should be employed. However, since there are concerns about increased CH₄ emission from decomposing organic material during the cropping season, additional research on appropriate organic material sources and application methods should be conducted.

Changes in soil carbon and nitrogen accessibility with the application of biochars with different morphological and physical characteristics

The recent literature indicates that, depending on the feedstocks and pyrolysis temperature, biochar can be a good source of nutrients. On the contrary, some biochars are not good sources of available carbon and other nutrients, but their porous structure seems to be a suitable microenvironment for microbial colonization. We investigated the response of soil biological parameters, microbial biomass carbon and nitrogen (MBC and MBN), in relation to mobile N species. Five different biochars were produced at different temperatures (300, 350, 400, 450, and 500 °C) from the same feedstock (woodchips). The physicochemical and morphological characteristics of the individual biochar samples were described, and incubation was carried out with the application of 2% biochar to two different soil types (luvisol and fluvisol). The addition of 2% biochar did not change the pH in the slightly acid soils used in the experiment, in spite of the alkaline character of biochar. The increasing amounts of total and nitrate-available nitrogen during the experiment are probably related to changes in soil microbial activity. The amount of soluble carbon was constant during the experiment, confirming its stability in the soil, most likely because of the high amount of lignin in the feedstock. The influence of biochar on the soil microbiome was determined on the basis of the concentrations of MBC and MBN. Microbial biomass was increased in both soils treated with biochar produced at lower temperatures. The physicochemical characteristics of the biochar as well as the sorption behavior of N-NO3− and N-NH4+ indicate that at a pyrolysis temperature of 400 °C, biochar properties change substantially. However, these findings are only valid for biochar produced from woodchips, and the long-term effects of biochar application on soil properties need to be investigated in further studies.