Simulation of conservation tillage effect on soil organic carbon (SOC) stock on the national scale is essential for Tier 3 level greenhouse gas inventory in the agricultural sector. However, the ...conservation tillage effects varied depending on different soil conditions, potentially leading to inaccurate national assessments. This study aimed to propose a framework for estimating the national scale impact of conservation tillage on SOC. As even in the most commonly used SOC dynamic model, the Rothamsted Carbon Model (RothC), does not reflect the conservation tillage effect in an explicit way, we modified it by developing the tillage rate modifiers (TRMs). First, we investigated the conditions for the inconsistent conservation tillage effects using the decision tree analysis based on 210 field experiment data from the mid-latitude region. The results highlighted that soil sand content and the existing SOC stock were the main factors driving the inconsistencies. After we categorized into four distinctive conditions, the TRMs for each condition were parameterized using a genetic algorithm. The average TRMs were 0.88 in the soils with sand content >37.6 % and 1.58 in the soils with sand content ≤37.6 %, indicating that conservation tillage is more effective in coarse-textured soil, and there is a risk of decreasing SOC stock in the latter condition. Using the modified RothC model, a three-step national-scale simulation framework was suggested: compiling country-specific data, establishing baseline and conservation tillage scenarios, and modeling conservation tillage effects with uncertainty analysis. Our approach also defined the maximum conservation tillage area, factoring in local cropping systems and soil conditions. Our refined RothC model with TRMs provides a nuanced understanding of conservation tillage effects, emphasizing the role of soil characteristics. The proposed national-scale simulation framework offers a reliable tool for evaluating conservation tillage impact on SOC, ensuring more accurate greenhouse gas inventories in agriculture.
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•The effect of conservation tillage on SOC stock showed significant inconsistency.•Soil sand content and initial SOC stock drive conservation tillage inconsistencies.•Tillage rate modifiers for RothC model were developed separately for different soil conditions.•Enhanced RothC model reflects variances in tillage effects across middle-latitude region.•A national-scale framework to evaluate the potential of conservation tillage were suggested.
To ensure the safety of carbon capture and storage (CCS) technology, insight into the potential impacts of CO2 leakage on the ecosystem is necessary. We conducted a greenhouse experiment to ...investigate the effects of high soil CO2 on plant growth and the soil environment. Treatments comprised 99.99% CO2 injection (CG), 99.99% N2injection (NG), and no injection (BG). NG treatment was employed to differentiate the effects of O2 depletion from those of CO2 enrichment. Soil CO2 and O2 concentrations were maintained at an average of 53% and 11%, respectively, under CG treatment. We verified that high soil CO2 had negative effects on root water absorption, chlorophyll, starch content and total biomass. Soil microbial acid phosphatase activity was affected by CG treatment. These negative effects were attributed to high soil CO2 instead of low O2 or low pH. Our results indicate that high soil CO2 affected the root system, which in turn triggered further changes in aboveground plant tissues and rhizospheric soil water conditions. A conceptual diagram of CO2 toxicity to plants and soil is suggested to act as a useful guideline for impact assessment of CCS technology.
Roadside greenery is an efficient strategy for maximizing ecosystem services, including carbon sequestration in urban settings. However, the quantification of carbon sequestration is not ...comprehensive because understory shrubs and soil respiration have not been thoroughly considered. We developed an integrated methodology that combined field measurements and greenhouse incubation to comprehensively assess carbon sequestration in roadside greenery systems. The system was defined as an 8 m long section comprising a single tree (Zelkova serrata), 79 shrubs (Euonymus japonicus), and soil. Annual carbon uptake by a tree was estimated using an allometric equation derived from an official government report. For shrubs, carbon uptake was measured in the field by monitoring CO2 concentration change in the chamber enclosing the leaves and stems. Annual carbon uptake by shrubs was estimated by using the regression equation among carbon uptake, air temperature, and photosynthetically active radiation. We also estimated shrub root respiration by combining net primary production (NPP) from the greenhouse incubation and measured pruning effect in the field. This enabled us to differentiate heterotrophic respiration from the total soil respiration. The overall methodology accurately assessed net ecosystem production (NEP) from the roadside greenery system, which is 0.528 kg C m−2 yr−1. If this figure is extended to all roads in the target city, it can offset daily carbon emitted from the total registered passenger vehicles in the target city. Considering that shrubs sequester an amount equivalent to 29.3 % of the carbon sequestered by tree species, the current greenhouse gas inventory should include shrubs as an important carbon sink. As we also revealed that roadside soil has high carbon vulnerability, proper soil management is needed to enhance NEP. Our systematic approach evaluating the carbon balance within the roadside greenery system can be applied to other cities, contributing to enhance global understanding of urban carbon cycle.
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•Urban roadside C balance was systematically analyzed including shrubs and soil.•The amount of carbon uptake by shrubs corresponds to 29.3 % of that by a tree.•Proper soil management of roadside greenery can enhance the carbon sequestration.
While there are extensive studies reporting a reduction in N2O emission by biochar addition, there are some cases that showed an increase in N2O emission. To identify the primary conditions that lead ...to an increase in N2O emissions, we conducted a decision tree analysis of 148 observations from 25 published papers. It was verified that biochar made with rice husk, rice straw, nut-shell, pits, and stones had a higher chance of increasing N2O emissions than biochar made with wood, herbaceous, and biosolid. Moreover, it was also demonstrated that the probability of increasing N2O emission by former group biochar was higher in the low pH soils. The latter group of biochar showed the lowest probability of increasing N2O emission in soil with low soil organic carbon (SOC) content. The decision tree analysis results led us to conduct an incubation experiment to understand the underlying mechanisms under which conditions biochar increases or decreases soil N2O emissions. The soils amended with urea and 4% (w/w) biochars (cocopeat: CPB, rice husk biochar: RHB, and wood pellets: WPB) were incubated for 15 days on aerobic condition. As a result, N2O emissions increased in the soils amended with CPB and RHB, which was consistent with decision tree analysis. The high labile matter content of these biochar could stimulate both heterotrophic denitrification and nitrification-mediated processes. In the soil with the high labile matter biochar which increased soil pH throughout the experimental period (CPB treatment), NO2− was accumulated and gene abundance of nitrite-oxidizing bacteria were reduced, which might be caused by NH3 toxicity. Our results can be utilized as a practical guideline to maximize biochar's climate change mitigation potential.
•We identified conditions that biochar increase N2O emission in non-flooded soil.•Biochar with a low C/N ratio has a higher chance of increasing soil N2O emissions.•The probability of increasing N2O emission was higher where biochar raises soil pH.•Labile matter of biochar stimulated both the nitrification and denitrification processes.
Biochar amendment of upland soil has been generally accepted to mitigate nitrous oxide (N2O) emissions. However, this is not always the case in rice paddy soil, and the underlying mechanisms are not ...well understood. To evaluate how biochar amendment affects N2O production and emissions in paddy soil, an incubation experiment was designed including six treatments: wheat straw-derived biochar (slow pyrolyzed at 400 °C) amendment at rates of 0% (Control), 1% and 4% soil mass (w/w), inorganic nitrogen (N) fertilizer amendment (with urea), and N fertilizer plus 1% biochar and 4% biochar. The application of 4% biochar significantly increased N2O emissions from N-unfertilized and fertilized soils during the 45-day incubation, by 291% and 256%, respectively, while 1% biochar amendment significantly increased soil N2O emissions when accompanied by N fertilizer addition. On day 14, when the N2O emission peaks occurred, N2O flux was significantly correlated with soil pH in all treatments. Biochar addition also enhanced the abundance of ammonia-oxidizing bacteria (AOB) amoA genes, which was significantly related to soil pH. Among all detected N2O-forming and reducing microbial genes, the abundance of AOB amoA genes was most closely related to N2O flux. On biochar addition, the AOB community structure shifted from Nitrosospira-dominated toward Nitrosomonas, and the diversity of AOB was significantly increased. Compared with the control, biochar amendment decreased, albeit not significantly, the abundance of the nitrous oxide reductase encoding gene nosZ, but did not alter the abundance of nitrite reductase encoding genes nirK and nirS. Our study suggests that wheat straw-derived biochar amendment of paddy soils increased soil pH, which in turn increased the abundance and diversity of AOB and N2O emissions.
•Biochar significantly stimulated N2O emission from paddy soils.•Biochar increased soil pH and bacterial amoA gene abundance.•Increased N2O emission was mainly due to increased bacterial amoA gene abundance.•Biochar shifted the community structure of AOB from Nitrosospira toward Nitrosomonas.•Biochar reduced the abundance of the nosZ gene but did not alter nirK and nirS levels.
•Biochar alleviated drought conditions by improving soil physical structure.•Enhanced macro-aggregation by biochar might increase the formation of meso-pores.•Meso-pores could retain more soil water ...for plant uptake.•Biochar is one of promising strategies for mitigating drought in urban roadside greenery.
Soil structure degradation is a major obstacle to vegetation growth in urban roadside greenery, particularly under drought conditions. Biochar application can improve soil structure and water retention; however, the mechanisms linking changes in soil aggregation with those in pore size distribution, and how they interactively influence plant growth remain unclear. In this study, we investigated the role of biochar in improving soil structure and water retention under drought stress in urban roadside greenery. In a field study, plots (2 m × 2 m) were established on roadside greenery in Suwon, Korea, in which 2.5% wt bochar was mixed with surface soil (<10 cm depth) (BCfield). During the eight-month experiment, drought conditions prolonged, and soil water content was continuously higher in BCfield than in CONfield. For a more mechanistic understanding, a 100-day greenhouse experiment was conducted on Rudbeckia hirta planted in sandy soil, either mixed with 4% wt biochar (BCgreenhouse) or without biochar (CONgreenhouse). Drought conditions were simulated by maintaining soil water content below 40% of the water-holding capacity. In the biochar-added soil, macro-aggregates (250–1000 μm) increased significantly after 60 days, probably due to biochar particles themselves acting as the same-sized aggregates. In addition, biochar can act as a binding agent for forming macro-aggregates, thereby preventing their disintegration into smaller-sized aggregates. Enhanced macro-aggregation in biochar-added soil, therefore, is a potential mechanism for the increased formation of meso-pores. These pores could retain more soil water for plant uptake, eventually increasing plant biomass and water use efficiency in the BCgreenhouse, by 39%, when compared with that in the CONgreenhouse under drought conditions. Our results indicate that biochar application is a potential management strategy for improving soil physical structure in urban roadside greenery, which would, in turn increase plant resistance and resilience to drought stress.
Biochar has been proposed as a promising amendment that may improve soil structure. However, our understanding how it mitigates extreme soil water stress in roadside soils is limited. In this study, ...we investigated the effects of biochar on soil properties and plant growth under extreme water stress conditions. A greenhouse experiment was conducted on two-year-old Gingko biloba saplings planted in pots with sandy soil only (CON) and with sandy soil mixed with biochar (BC). To simulate excessive water stress conditions, we increased the soil water-filled pore space up to the saturation level throughout the experimental period. We also simulated the switching water conditions by maintaining the saturation condition for 30 days, followed by no addition of water. The BC treatment significantly influenced the aggregate distribution and enhanced the proportion of macroaggregates (>250 μm). The biochar itself also functioned as a macroaggregate and contributed to increased aeration under the excessive water condition. Under the switching water condition, the micropores within the biochar might have helped maintain the available water for plant roots and soil microbes. Plant growth was significantly higher in the BC than CON soils for both the excessive and switching water sets. In the BC soils, plant growth was higher in the excessive than in the switching water sets, indicating that the soil water status in our BC treatment for the excessive water set was not stressful enough to inhibit plant growth. The % optimal water condition, which is defined as the proportion of days when the soil water status is within the least limiting water range, had a very high explanatory power to explain the plant growth (r = 0.7172, p < 0.0001). Our results indicate that biochar can alleviate water stresses in urban roadside soils by retaining plant available water under the wet and dry conditions.
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•Macro-sized biochar maintained soil structure under extreme water conditions.•Biochar alleviated soil water stress by improving drainage and water maintenance.•Moderating role of biochar in extreme soil water conditions enhanced plant growth.•Biochar is one of promising soil amendments for urban roadside tree systems.
The soils in urban greenery provide essential ecosystem services. However, only a few studies have assessed urban soil quality based on a comprehensive view of ecosystem services and soil ...multi-functionality. In this study, we suggest an urban soil quality index (uSQI) to evaluate soil status in various spatial types of urban greenery. Our objectives are 1) to develop an uSQI incorporating a range of urban soil ecosystem services in metropolitan environments and 2) to test the efficacy of the developed uSQI by applying it to nine different sites. To fully consider ecosystem services provided by the urban soil, a DPSC (drivers and pressures, state, and changes) framework was constructed. Drivers and pressures are influencing factors that continuously alter the state of the urban greenery, eventually leading to changes in ecosystem services and soil functions. The six soil functions considered were physical stability and support, water storage and infiltration, habitat provision, organic matter stabilization, nutrient supply and retention, and pollutant immobilization and decomposition. These functions were measured using ten soil indicators which can be quantified: bulk density, saturated hydraulic conductivity, litter-layer depth, mineral-associated organic matter, clay+silt content, fluorescein diacetate hydrolytic activity, cation exchange capacity, inorganic nitrogen concentration, pH, and concentrations of potentially toxic elements. The uSQI was calculated as the arithmetic mean of the scores of the six soil functions, obtained through the fuzzy logic functions. The uSQI successfully identified the low soil quality sites among nine urban greeneries with different spatial types (point, line, and polygon). In addition, we could examine the degraded soil function of each site and suggest a management guideline using our uSQI. Our novel index can help urban stakeholders evaluate and monitor the soil quality of urban greenery.
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•Soils of urban greenery provide various ecosystem services but are often impaired.•A novel urban soil quality index (uSQI) is presented for soil quality assessment.•uSQI comprehensively considered ecosystem services and functions of urban soil.•uSQI successfully identified the low soil quality sites and degraded functions.
Although a meta-analysis on biochar's effects on N2O emission reported an overall reduction in N2O emission by adding biochar to the soils, there are still variations in the changes in N2O emission, ...especially from field results. The objectives of this study are 1) to compare the effects of biochar addition on N2O emission between three agricultural upland field experiments, where soil water status was dry favoring nitrification and 2) to identify main factors explaining biochar's variable effects on N2O emission. Three field experiments were conducted: Exp A in the cultivated grassland treated with rice husk biochar at 2 ton ha−1 + urea (CHAR) and with urea only (CON); Exp B in the cabbage field with CHAR and CON treatments; and Exp C in the pepper field with CHAR, CON, and CHAR + DCD (dicyandiamide, nitrification inhibitor) treatments. In Exp A and C, cumulative N2O emissions significantly increased by 82.5% and 55.8% in the CHAR than CON treatments, respectively, while in Exp B, there was no difference in cumulative N2O emission between the CHAR and CON. Based on results from using nitrification inhibitor and soil % water filled pore space (WFPS), we assumed that the main N2O production mechanism was nitrification. Our results suggest that soil water status right after urea application is the primary determinant of different effects of biochar on N2O emission in addition to soil C status and biochar's adsorption. Principal component analysis using the 25 compiled data also supported our results. This study identified the specific field conditions under which biochar could have stimulating effects on N2O emission. Mitigation potential of biochar application should be reconsidered if biochar and urea were amended to dry soils with low C contents.
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•N2O emissions were increased or not changed when both biochar and urea were applied to dry soils with low C content.•Soil water status right after urea and biochar application was the primary determinant to predict the effect of biochar on N2O emissions, together with soil C status and biochar's adsorptive capacity.•Our study is unique in that we obtained the results from multiple field experiments covering the whole cropping periods.
Vegetation monitoring can be used to detect CO2 leakage in carbon capture and storage (CCS) sites because it can monitor a large area at a relatively low cost. However, a rapidly responsive, ...sensitive, and cost-effective plant parameters must be suggested for vegetation monitoring to be practically utilized as a CCS management strategy. To screen the proper plant parameters for leakage monitoring, a greenhouse experiment was conducted by exposing kale (Brassica oleracea var. viridis), a sensitive plant, to 10%, 20%, and 40% soil CO2 concentrations. Water and water with CO2 stress treatments were also introduced to examine the parameters differentiating CO2 stress from water stresses. We tested the hypothesis that chlorophyl fluorescence parameters would be early and sensitive indicator to detect CO2 leakage. The results showed that the fluorescence parameters of effective quantum yield of photosystem II (Y(II)), detected the difference between CO2 treatments and control earlier than any other parameters, such as chlorophyl content, hyperspectral vegetation indices, and biomass. For systematic comparison among many parameters, we proposed an indicator evaluation score (IES) method based on four categories: CO2 specificity, early detection, field applicability, and cost. The IES results showed that fluorescence parameters (Y(II)) had the highest IES scores, and the parameters from spectral sensors (380–800 nm wavelength) had the second highest values. We suggest the IES system as a useful tool for evaluating new parameters in vegetation monitoring.
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