Soil Carbon Content Research Articles

Effect of laser wavelength on soil carbon measurements using laser-induced breakdown spectroscopy.

We investigate the effect of laser wavelength on laser-induced breakdown spectroscopy (LIBS) on the measurement of carbon in agricultural soils. Two laser wavelengths, 1064 nm and 532 nm, were used to determine soil carbon concentration. No chemical pretreatment, grinding, or pelletization was performed on soil samples to simulate in-field conditions. A multivariate calibration model with outlier filtering and optimized parameters in partial least squared regression (PLSR) was established and validated. The calibration model estimated carbon content in soils with an average prediction error of 4.7% at a laser wavelength of 1064 nm and 2.7% at 532 nm. The limit of detection (LOD) range for 532 nm was 0.34-0.5 w/w%, approximately half of the LOD range for 1064 nm laser wavelength. The improvement in prediction error and LOD of LIBS measurements is attributed to the increase in plasma density achieved at 532 nm.

Bioenergy crop Miscanthus x giganteus acts as an ecosystem engineer to increase bacterial diversity and soil organic matter on marginal land

Cultivation of the bioenergy and bioproduct crop Miscanthus x giganteus (Miscanthus) on marginal lands (including those that are anthropogenically damaged) is attractive due to the robust growth of Miscanthus, leading to high yields even under stressful environmental conditions. Miscanthus growth and production may also build soil carbon, which is favorable for land restoration and climate change mitigation. Gaps in our understanding of the mechanisms facilitating soil carbon accumulation under Miscanthus persist, particularly regarding the role of the soil microbiome in facilitating these processes, and how land use histories (e.g. past disturbances) and management strategies (e.g., fertilizer additions) affect these mechanisms. To address these knowledge gaps, we measured plant performance, soil properties, and microbial parameters over the first three years of Miscanthus establishment across a gradient of land disturbance intensity and different fertilization strategies (none, organic, conventional). We determined that plant performance (e.g., aboveground biomass yield) increased over time during establishment under all disturbance intensities but remained lower overall at the most intensely disturbed site. Across all sites, bacterial diversity and microbial carbon use efficiency increased over time and were positively correlated with soil organic matter. We also observed increases in the relative abundance of key plant growth promoting microbes (e.g., mycorrhizal fungi and bacterial N-fixers). There was no effect of nutrient addition on plant yield, soil carbon concentrations, or microbial carbon use efficiency. All told, our results suggest that Miscanthus consistently increases microbial diversity and carbon use efficiency, facilitating soil organic matter accumulation across sites despite varying land use histories and soil properties. In this way Miscanthus acts as an ecosystem engineer, improving soil biological and chemical properties such that highly disturbed soils come to resemble less disturbed systems over time.

Characterization of plant growth promoting potential of 3D-printed plant microbial fuel cells

Plant-Microbial Fuel Cell (PMFC) is an emerging technology that converts plant waste into electrical energy through rhizodeposition, offering a renewable and sustainable source of energy. Deviating from the traditional PMFC configurations, additive manufacturing was utilized to create intricate and efficient designs using polymer-carbon composites. Concerning the agricultural sector, the effect of 3D-printed PMFCs on the growth and biomass distribution of Phaseolus lunatus and Ipomoea aquatica was determined. The experiment showed that electrostimulation promoted the average daily leaf number and plant height of both polarized plants, which were statistically proven to be greater than the control (α = 0.05), by energizing the flow of ions in the soil, boosting nutrient uptake and metabolism. It also stimulated the growth of roots, increasing the root dry mass of polarized plants by 155.44% and 66.30% for I. aquatica and P. Lunatus against their non-polarized counterpart. Due to the biofilm formation on the anode surface, the number of root nodules of the polarized P. lunatus was 51.30% higher than the control, while the protein content in the PMFC setup was 42.22% and 8.26% higher than the control for I. aquatica and P. lunatus, respectively. The voltage readings resemble the plants' average growth rate, and the polarization studies showed that the optimum external resistances in the I. aquatica- and P. lunatus-powered PMFC were 4.7 kΩ and 10 kΩ, respectively. Due to other prevailing pathways of organic carbon consumption, such as methanogenesis, the effect of polarization on the organic carbon content in soil is currently inconclusive and requires further study.

An assessment of Sentinel‐1 synthetic aperture radar, geophysical and topographical covariates for estimating topsoil particle‐size fractions

AbstractData derived from synthetic aperture radar (SAR) are widely employed to predict soil properties, particularly soil moisture and soil carbon content. However, few studies address the use of microwave sensors for soil texture retrieval and those that do are typically constrained to bare soil conditions. Here, we test two statistical modelling approaches—linear (with and without interaction terms) and tree‐based models, namely compositional linear regression model (LRM) and random forest (RF)—and both nongeophysical (e.g., surface soil moisture, topographic, etc) and geophysical‐based (electromagnetic, magnetic and radiometric) covariates to estimate soil texture (sand %, silt % and clay %), using microwave remote sensing data (ESA Sentinel‐1). The statistical models evaluated explicitly consider the compositional nature of soil texture and were evaluated with leave‐one‐out cross‐validation (LOOCV). Our findings indicate that both modelling approaches yielded better estimates when fitted without the geophysical covariates. Based on the Nash–Sutcliffe efficiency coefficient (NSE), LRM slightly outperformed RF, with NSE values for sand, silt and clay of 0.94, 0.62 and 0.46, respectively; for RF, the NSE values were 0.93, 0.59 and 0.44. When interaction terms were included, RF was found to outperform LRM. The inclusion of interactions in the LRM resulted in a decrease in NSE value and an increase in the size of the residuals. Findings also indicate that the use of radar‐derived variables (e.g., VV, VH, RVI) alone was not able to predict soil particle size without the aid of other covariates. Our findings highlight the importance of explicitly considering the compositional nature of soil texture information in statistical analysis and regression modelling. As part of the continued assessment of microwave remote sensing data (e.g., ESA Sentinel‐1) for predicting topsoil particle size, we intend to test surface scattering information derived from the dual‐polarimetric decomposition technique and integrate that predictor into the models in order to deal with the effects of vegetation cover on topsoil backscattering.

Biochar combined with different nitrogen fertilization rates increased crop yield and greenhouse gas emissions in a rapeseed-soybean rotation system

Biochar as agricultural soil amendment has been extensively investigated for its potential to sequester carbon, to mitigate greenhouse gases (GHGs) emissions, to enhance soil fertility and enhance crop yields. In this study, we investigated the impact of varying N fertilization rates in conjunction with biochar on soil properties, crop yield, and GHGs emissions in a rapeseed (Brassica napus L.)-soybean (Glycine max (L.) Merrill) rotation system for one year. Biochar and N fertilizer were applied following a factorial combination design of three biochar (B0: 0 t hm−2, B1: 15 t hm−2, and B2: 60 t hm−2) and three N fertilizer application rates (H: 100%, M: 75%, and L: 50% of the conventional application rates). In general, there was no significant effect of N fertilizer and its interaction with biochar application on soil water content, pH, and total carbon content, but the addition of biochar significantly increased these parameters (P < 0.05). The yield of both crops were significantly augmented by biochar up to 75% compared to using N fertilization alone, potentially due to enhanced N use efficiency. However, biochar significantly increased the cumulative N2O and CH4 emissions by as much as 2.2 times and 19 times, respectively, during the rapeseed season, thereby elevating the global warming potential (GWP) and the yield-scaled GWP. Nevertheless, the significantly increased soil carbon content following biochar addition might boost soil carbon sequestration, which could counterbalance the escalating GWP induced by GHGs. Therefore, we recommend a comprehensive and long-term evaluation of biochar's impact by considering crop yield, GHGs emissions, and carbon sequestration in agricultural systems to ensure sustainable agricultural management.

The Impact and Invasive Mechanisms of Pueraria montana var. lobata, One of the World's Worst Alien Species.

Pueraria montana var. lobata is native to East Asia, and was introduced to many countries due to its potential for multiple uses. This species escaped under the management conditions soon after its introduction, and became a harmful weed species. This species has been listed in the top 100 of the world's worst invasive alien species. P. montana stands expand quickly and threaten the native flora and fauna including microbiota. This species affects the concentration of carbon and nitrogen in soil and aquatic environments, and increases the amount of pollutants in the local atmosphere. Its infestation also causes serious economic losses on forestry and agriculture. Its characteristics of fast growth, thick canopy structure, enormous vegetative reproduction, and adaptative ability to the various environmental conditions may contribute to the invasiveness and naturalization of this species. The characteristics of P. montana regarding their defense functions against their natural enemies and pathogens, and allelopathy may also contribute to the invasiveness of this species. Potential allelochemicals such as xanthoxins, p-coumaric acid, caffeic acid, methyl caffeate and daidzein, and two isoflavones with anti-virus activity were identified in this species. In addition, fewer herbivore insects were found in the introduced ranges. These characteristics of P. montana may be involved in the invasive mechanisms of the species. This is the first review article focusing on the invasive mechanisms of this species.

Deterministic Development of Soil Microbial Communities in Disturbed Soils Depends on Microbial Biomass of the Bioinoculum.

Despite its enormous importance for ecosystem services, factors driving microbial recolonization of soils after disturbance are still poorly understood. Here, we compared the microbial recolonization patterns of a disturbed, autoclaved soil using different amounts of the original non-disturbed soil as inoculum. By using this approach, we manipulated microbial biomass, but did not change microbial diversity of the inoculum. We followed the development of a new soil microbiome after reinoculation over a period of 4 weeks using a molecular barcoding approach as well as qPCR. Focus was given on the assessment of bacteria and archaea. We could show that 1 week after inoculation in all inoculated treatments bacterial biomass exceeded the values from the original soil as a consequence of high dissolved organic carbon (DOC) concentrations in the disturbed soil resulting from the disturbance. This high biomass was persistent over the complete experimental period. In line with the high DOC concentrations, in the first 2 weeks of incubation, copiotrophic bacteria dominated the community, which derived from the inoculum used. Only in the disturbed control soils which did not receive a microbial inoculum, recolonization pattern differed. In contrast, archaeal biomass did not recover over the experimental period and recolonization was strongly triggered by amount of inoculated original soil added. Interestingly, the variability between replicates of the same inoculation density decreased with increasing biomass in the inoculum, indicating a deterministic development of soil microbiomes if higher numbers of cells are used for reinoculation.

Effects of Combined Application of Biochar and Different Types of Nitrogen Fertilizers on Rapeseed Root Growth and Properties of Purple Soil in Southwest China

To demonstrate the effects of combined application of biochar and different types of nitrogen fertilizers on the growth of plant roots and on purple soil properties such as soil nutrients, soil carbon content and soil respiration, a 206-day greenhouse pot experiment with rapeseed was conducted. Three types of nitrogen fertilizer were used: urea (UR), controlled-release urea (RU), a mixture of 60% urea and 40% controlled-release urea (40% RU), and biochar was added at mass fractions of 0% (C0), 2% (C1) and 4% (C2), with a control treatment (CK) without nitrogen fertilizer and biochar. The results showed that biochar significantly improved soil nutrient status, with the best effect observed when 40%RU was co-applied with biochar. The addition of biochar significantly increased soil total organic carbon (TOC) and particulate organic carbon (POC). Soil respiration increased with increasing biochar application, and the combination of 2% biochar and 40% RU showed a reduction in carbon emissions compared to the UR and RU treatments. The number of rapeseed root tips (NT), forks (NF) and crossings (NC) increased significantly with the addition of biochar, and the combination of biochar and 40% RU was more beneficial for root growth and development than RU and UR. Considering the improvement in soil nutrition, increased soil organic carbon content, reduced carbon emissions, and enhanced rapeseed growth and development, the co-application of 2% biochar and 40% RU is recommended for large-scale application in rapeseed cultivation in the hilly purple soil of southwest China.

Variations in Microbial Residue and Its Contribution to SOC between Organic and Mineral Soil Layers along an Altitude Gradient in the Wuyi Mountains

Microbes are crucial components of soil, and their residue carbon plays a significant role in the formation and stabilization of soil carbon pools. However, current research on microbial residue carbon has predominantly focused on surface soils, with limited studies on deep soils. The patterns of variation along soil profiles and their controlling factors remain unclear. Therefore, this study aimed to investigate the soils from different elevations in the Wuyi Mountains, specifically focusing on the organic layers (0–10 cm) and mineral layers (30–40 cm). Amino sugars were utilized as biomarkers for the microbial residue, and the RDA (redundancy analysis) method was employed to analyze the patterns of microbial residue carbon in different soil layers and to identify the factors that control them. The results indicate that there are significant differences in the microbial residue carbon content and its contribution to soil organic carbon (SOC) between the different soil layers. Specifically, between the organic layer and the mineral layer, the microbial residue carbon content exhibited an increasing trend, whereas its contribution to SOC decreased. This finding suggests that soil layer type has a notable impact on microbial residue carbon content and its contribution to SOC. Moreover, fungal residue carbon content was found to be higher than bacterial residue carbon content in both soil layers. However, the ratio of fungal residue carbon to bacterial residue carbon gradually decreased between the organic layer and the mineral layer. This implies that although fungal residue carbon remains dominant, the contribution of bacterial residue carbon to the soil carbon pool increases as the soil transitions to the mineral layer. The total soil carbon content, elevation, and C/N ratio exhibited positive correlations with fungal and bacterial residue carbon, indicating their significant roles in the accumulation of microbial residue carbon in soils. Notably, elevation emerged as a key regulating factor in the accumulation of microbial residue carbon, explaining 85.8% and 67.9% of the variations observed in the organic layer and the mineral layer respectively. These research findings contribute to a better understanding of the soil carbon cycling process and its mechanisms, providing a scientific basis for developing strategies to enhance soil carbon sequestration by manipulating micro-organisms.

Positive and Negative Impact of Nitrogen Fertilizer on Soil Properties and Nutrient Dynamic

Our study was conducted over the period of two years and explored the impact of nitrogen fertilization and non-fertilization systems on soil health indicators and crop yield. Our study hypothesized that no fertilization coupled with cover cropping would enhance soil health, carbon content, and bulk density. This study found that excessive nitrogen fertilization had negative impact on soil health factors such as bulk density increment and carbon content decline through deeper profiles. In contrast, the no-fertilization system exhibited improved bulk density and better carbon distribution near the soil surface, suggesting that reducing or eliminating nitrogen can promote soil health and prevent long-term fertility decline. The study also highlighted the imbalanced carbon to nitrogen ratio resulting from high nitrogen fertilizer rate can negatively impact soil microbial activity and nutrient mineralization.

Ligneous amendments increase soil organic carbon content in fine-textured boreal soils and modulate N2O emissions.

Organic soil amendments are used to improve soil quality and mitigate climate change. However, their effects on soil structure, nutrient and water retention as well as greenhouse gas (GHG) emissions are still poorly understood. The purpose of this study was to determine the residual effects of a single field application of four ligneous soil amendments on soil structure and GHG emissions. We conducted a laboratory incubation experiment using soil samples collected from an ongoing soil-amendment field experiment at Qvidja Farm in south-west Finland, two years after a single application of four ligneous biomasses. Specifically, two biochars (willow and spruce) produced via slow pyrolysis, and two mixed pulp sludges from paper industry side-streams were applied at a rate of 9-22 Mg ha-1 mixed in the top 0.1 m soil layer. An unamended fertilized soil was used as a control. The laboratory incubation lasted for 33 days, during which the samples were kept at room temperature (21°C) and at 20%, 40%, 70% or 100% water holding capacity. Carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) fluxes were measured periodically after 1, 5, 12, 20 and 33 days of incubation. The application of ligneous soil amendments increased the pH of the sampled soils by 0.4-0.8 units, whereas the effects on soil organic carbon content and soil structure varied between treatments. The GHG exchange was dominated by CO2 emissions, which were mainly unaffected by the soil amendment treatments. The contribution of soil CH4 exchange was negligible (nearly no emissions) compared to soil CO2 and N2O emissions. The soil N2O emissions exhibited a positive exponential relationship with soil moisture. Overall, the soil amendments reduced N2O emissions on average by 13%, 64%, 28%, and 37%, at the four soil moisture levels, respectively. Furthermore, the variation in N2O emissions between the amendments correlated positively with their liming effect. More specifically, the potential for the pulp sludge treatments to modulate N2O emissions was evident only in response to high water contents. This tendency to modulate N2O emissions was attributed to their capacity to increase soil pH and influence soil processes by persisting in the soil long after their application.

Afforested and abandoned land ecosystems exhibit distinct soil microbial biomass stoichiometric homeostasis over chronosequence

AbstractRevegetation influences microbial biomass stoichiometry by altering the substrate conditions, yet the differences in microbial stoichiometry homeostasis and the underlying drivers under different revegetation approaches remain unexplored. Here, we selected sites across three age classes of Robinia pseudoacacia plantation (RP) and abandoned land (AL), and quantified the microbial stoichiometric characteristics during farmland‐initiated restoration. Plant community composition, leaf and soil nutrients, and microbial community composition and diversity were also measured. We found that revegetation of former farmland under both restoration types resulted in non‐isometric changes in soil carbon (C), nitrogen (N), and phosphorus (P) contents, that is, decoupling of soil C and N from P. However, AL and RP succession exhibited homeostatic and plastic microbial biomass stoichiometry, respectively, in response to altered substrate stoichiometry. These differences were associated with adjustments in the above‐ and belowground biomes. Specifically, the synergistic increase of Compositae and Actinobacteria in the late AL succession allowed the ecosystem to reduce P demand and maintain microbial stoichiometric homeostasis. In contrast, higher leaf C and N input during RP succession may have resulted excessive microbial storage of elements, which in turn leads to stoichiometric convergence between microbial biomass and soil resources. In addition, RP succession caused changes in microbial community structure, mainly the continuous increase of Proteobacteria (copiotrophs, r‐strategists), which also potentially increased the requirement for resources to maintain homeostasis and ensure the rapid growth. These findings demonstrate that AL has a comparatively greater efficacy in maintaining microbial stoichiometric homeostasis during long‐term revegetation. Our study also highlights the importance of appropriately managing existing RP plantations to alleviate the pressure of P deficiency and sustainably maintain this fragile ecosystem.

Analysis on Change in Soil Organic Carbon Content of Farmland in Yangtze River Economic Belt Under Different Fertilizing Measures

The literature from a long-term fertilization experiment in the Yangtze River Economic Belt from January 1992 to May 2022 was collected, and the data of farmland soil organic carbon were extracted and integrated. Using the normalization treatment and the analysis method of relative annual variation, the overall change in soil organic carbon content in farmland in the Yangtze River Economic Belt under different long-term fertilization measures was studied, and the change differences of soil organic carbon content under three tillage modes were compared so as to judge and analyze the influence of the duration of the experiment on soil organic carbon dynamics. The results showed that under different long-term fertilization measures, the organic carbon content of farmland soil in the Yangtze River Economic Belt in China showed an overall upward trend. The NP, NPK, O, and NPKO treatments all increased the organic carbon content of agricultural soils, with that of the NPKO treatment being the largest. The sole application of inorganic nitrogen fertilizer reduced the organic carbon content of the soil. The rates of change in soil organic carbon content were 0.22 g·(kg·a)-1, 0.24 g·(kg·a)-1, and 0.16 g·(kg·a)-1for dryland, paddy, and water-dry rotation farmland, respectively. Additionally, the relatively rapid increase effect of organic carbon brought by the O and NPKO treatments could last for no more than 28 years in dryland soil but could still last for more than 28 years in paddy field and paddy-upland rotation soil. There was some variation in the rate of change of soil organic carbon content between soil types. The average rate of change of organic carbon was 0.25 g·(kg·a)-1for red soils, 0.14 g·(kg·a)-1 for brown soils, 0.19 g·(kg·a)-1 for tidal soils, and 0.15 g·(kg·a)-1 for rice soils. The trend of NPKO>O>NPK>NPK>NP>N was basically maintained for the rate of change in soil organic carbon content. The NPKO treatments were all significantly higher than the chemical fertilizer (N, NP, and NPK) treatments alone. The N treatment showed a reduction in organic carbon content in both red soil and rice soils. Considering the carbon fixation of farmland soil, the combined application of organic and inorganic fertilizers is a more suitable fertilization method in this area.

Impact of Climate Warming on Paddy Soil Organic Carbon Change in the Sichuan Basin of China

Climate warming can increase soil temperature and lead to soil carbon release, but it can also increase soil organic carbon by increasing primary productivity. Cropland soils are considered to have a huge potential to sequester carbon; however, direct observations for the responses of cropland soil organic carbon to climate warming over broad geographic scales are rarely documented. Paddy soil is one of the important cultivated soils in China. Based on the data of 2217 sampling points obtained during the second national soil survey and the data of 2382 sampling points collected during 2017-2019, this study analyzed the change characteristics of soil organic carbon content of paddy surface soil in Sichuan Basin of China and explored the relationships between the soil organic carbon change of paddy soil and temperature, precipitation, cropland use type, fertilization intensity, and grain yield. The results showed that the content of soil organic carbon of paddy soil changed from 13.33 g·kg-1to 15.96 g·kg-1, with an increase of 2.63 g·kg-1, suggesting that soils in the Sichuan Basin have acted as a carbon sink over past 40 years. The soil organic carbon increment of paddy soil varied with different geomorphic regions and different secondary basins. The increase in SOC content in paddy soil was positively correlated with annual average temperature; negatively correlated with annual average precipitation; and initially increased and then decreased with annual average fertilizer application, annual average increase rate of fertilizer application, annual average grain yield, and annual average grain yield growth rate. The relationship between the increase in SOC content and the annual average temperature growth rate was different under different farmland utilizations, and the increase in the annual average temperature growth rate had significant effects with the increase in SOC content only on paddy-dryland rotation. These results indicate that the paddy soil organic carbon change in Sichuan Basin was co-affected by various factors, but climate warming was an important factor leading to the paddy soil organic carbon change, and its influence was controlled by the water conditions determined by farmland use.

Agricultural soil plastic as a hidden carbon source stimulates microbial activity and increases carbon dioxide emissions

Plastic film mulching is an important agricultural practice, but its accumulation in soil threatens soil health. Here, we explored the effects of plastic film on soil carbon cycling through microcosmic incubation and estimated the excess carbon dioxide (CO2) emissions of farmland soils through Meta-analysis. The results showed that plastic film released dissolved organic carbon (DOC) into the soil, which was rapidly used by microorganisms and accelerated the decomposition of soil organic carbon (SOC), increasing CO2 emissions. Soil moisture content and soil carbon content affected the rate of DOC release from plastic. We estimated that residual plastic film farmland in six northwest provinces of China, 1.39 × 105 tons of excess CO2 emissions in 2020. The soil excess CO2 emissions was influenced by polyethylene (PE) plastic concentration and soil type. Replace PE plastic film with biodegradable film, 1.05 × 106 tons of excess CO2 emissions, 7.5 times that of PE plastics.

Impact of organic fertilization by the digestate from by-product on growth, yield and fruit quality of tomato (Solanum lycopersicon) and soil properties under greenhouse and field conditions

BackgroundThe application of organic fertilizer is a sustainable approach to maintain soil fertility in agricultural crop production. In contrast to other organic fertilizers, the digestate from by-products of anaerobic digestion has not been well characterized in terms of its agronomic properties. In this study, different fertilization treatments were investigated to evaluate their impacts on growth, yield and fruit quality of tomatoes and on soil properties under greenhouse and field conditions. The experiments comprised a control (unfertilized) and three treatments with the same nitrogen dose: chemical fertilizer, digestate from by-product (organic fertilizer) and digestate combined with chemical fertilizer.ResultsThe results showed that the application of digestate significantly increased the growth and fruit quality of tomato including height, stem diameter, leaf chlorophyll content index, and photosynthetic rate of tomato plant and sugar–acid ratio, protein content, and ascorbic acid content of the fruit. The nitrate contents in tomato fruit were lower in the digestate treatment and digestate combined with chemical fertilizer treatment than in the chemical fertilizer. The digestate combined with chemical fertilization resulted in the greatest increase in tomato yield, up to 26.29% and 10.78% higher than that in the chemical fertilizer treatment under field and greenhouse conditions, respectively. Moreover, fertilization with digestate treatment and digestate combined with chemical fertilizer treatment increased soil fertility, including soil nitrogen and carbon contents, and enhanced soil enzyme activities under both field and greenhouse conditions. In addition, the growth, yield, and fruit quality of tomato were significantly correlated with soil chemical characteristics and soil enzyme activities.ConclusionsThe effects of digestate treatments to maintain a stable tomato yield and improve fruit quality may be due to the enhanced soil enzymatic activities and chemical properties. These results suggest that the use of digestate as a full or partial replacement for chemical fertilizer could improve the growth and fruit quality of tomato, maintain the yield, and reduce the use of inorganic fertilizers in tomato production.Graphical

Non-intrusive soil carbon content quantification methods using machine learning algorithms: A comparison of microwave and millimeter wave radar sensors

Agricultural and forestry biomass can be converted to biochar through pyrolysis gasification, making it a significant carbon source for soil. Applying biochar to soil is a carbon-negative process that helps combat climate change, sustain soil biodiversity, and regulate water cycling. However, quantifying soil carbon content conventionally is time-consuming, labor-intensive, imprecise, and expensive, making it difficult to accurately measure in-field soil carbon’s effect on storage water and nutrients. To address this challenge, this paper for the first time, reports on extensive lab tests demonstrating non-intrusive methods for sensing soil carbon and related smart biochar applications, such as differentiating between biochar types from various biomass feedstock species, monitoring soil moisture, and biochar water retention capacity using portable microwave and millimeter wave sensors, and machine learning. These methods can be scaled up by deploying the sensor in-field on a mobility platform, either ground or aerial. The paper provides details on the materials, methods, machine learning workflow, and results of our investigations. The significance of this work lays the foundation for assessing carbon-negative technology applications, such as soil carbon content accounting. We validated our quantification method using supervised machine learning algorithms by collecting real soil mixed with known biochar contents in the field. The results show that the millimeter wave sensor achieves high sensing accuracy (up to 100%) with proper classifiers selected and outperforms the microwave sensor by approximately 10%–15% accuracy in sensing soil carbon content.

Mammal traits and soil biogeochemistry: Functional diversity relates to composition of soil organic matter.

Mammal diversity affects carbon concentration in Amazonian soils. It is known that some species traits determine carbon accumulation in organisms (e.g., size and longevity), and are also related to feeding strategies, thus linking species traits to the type of organic remains that are incorporated into the soil. Trait diversity in mammal assemblages - that is, its functional diversity - may therefore constitute another mechanism linking biodiversity to soil organic matter (SOM) accumulation. To address this hypothesis, we analyzed across 83 mammal assemblages in the Amazon biome (Guyana), the elemental (by ED-XRF and CNH analysis) and molecular (FTIR-ATR) composition of SOM of topsoils (401 samples) and trait diversity (functional richness, evenness, and divergence) for each mammal assemblage. Lower mammal functional richness but higher functional divergence were related to higher content of carbonyl and aliphatic SOM, potentially affecting SOM recalcitrance. Our results might allow the design of biodiversity management plans that consider the effect of mammal traits on carbon sequestration and accumulation in soils.

Seasonal dynamics of soil nitrogen mineralization and their influencing factors during shrub anthropogenic introduction in desert steppe.

We selected enclosed grassland, grazed grassland and shrublands with different planting years (3, 12, 22 years)/densities (intervals of 2, 6, 40 m) to investigate soil N mineralization dynamics in the growing season (April-October) and its influencing factors during the process of desert steppe-degradation-shrub introduction. The results showed that soil moisture at 0-200 cm layer was decreased with increases of shrub age and density, and that the variations of soil moisture at 0-10 cm layer coincided with seasonal change. Compared with grazed grassland and enclosed grassland, the positive effect of shrubs on soil carbon, nitrogen and phosphorus contents first increased and then decreased with the increases of age and density. Moreover, soil N mineralization significantly varied across months and sites. Soil NO3- content and microbial biomass carbon and nitrogen were significantly higher from June to August. The proportion of NO3- to inorganic nitrogen significantly increased from 30.5% in enclosed grassland to 69.5% in shrublands. NH4+ content was mainly affected by months compared with sites. In the process of steppe-degradation-shrub introduction, the increases of shrub age and density significantly enhanced seasonal differences of soil nitrification and ammonification, but not on the seasonal mineralization of microbial biomass carbon and nitrogen. Soil NH4+ and NO3- contents were significantly and positively correlated with total nitrogen, organic carbon and N/P. Soil stoichiometric ratios (C/N and N/P) directly regulated N mineralization process.

Effects of thaw slump on soil bacterial communities on the Qinghai-Tibet Plateau

The rapid permafrost degradation caused by climate warming can lead to thermokarst development, which in turn greatly alter soil parameters and impact the soil bacterial communities. However, the effects of thermokarst development on soil bacterial communities largely remain unclear. Here we selected a typical thaw slump in the Qinghai-Tibet Plateau. We classified three microfeatures in the thaw slump areas, i.e., control, slumping and exposed and collected surface 30 cm soils at a depth interval of 10 cm using a soil auger. The results showed that thaw slump decreased soil carbon and nitrogen contents especially for the topsoil (0–10 cm). Thaw slump increased the relative abundance of Gemmatimonadaceae, but decreased the relative abundance of Micrococcaceae. The richness indices including OTU numbers, Ace, Chao 1 and Simpson indices were the largest in the exposed area and lowest in the slumped area, and these trends were opposite to the Shannon index. Correlation analysis revealed that the relative abundance of Micrococcaceae was negatively correlated with moisture, Anaerolineaceae was positively correlated with organic carbon content. The Nitrospira, RB41 and Gemmatimonadaceae were negatively associated with total nitrogen, but Anaerolineaceae and JG30-KF-CM45 were positivity correlated with total nitrogen. C/N ratio was positively correlated with RB41 but negatively correlated with JG30-KF-CM45. We concluded that soil organic carbon, total nitrogen and C/N ratio were the most important factors shaping the bacterial community structure among the three microfeatures. The bacterial community diversity was the highest in the exposed area and lowest in the slumping area. The bacterial structure community was related with total nitrogen, soil organic carbon contents and C/N ratios. Overall, our findings showed thaw slump can decrease soil organic carbon and nitrogen content for the surface soils in the alpine meadow and further change the soil bacterial communities.