Particulate Matter Organic Carbon Research Articles

Hydrodynamics Mediates Biogeochemical Dynamics of Particulate Organic Matter in the Shelf of the Northern South China Sea During Summer

AbstractEnvironmental conditions, physiology and community composition of phytoplankton and the carbon and nitrogen isotope signature (δ13CPOC and δ15NPN) of particulate organic matter (POM) often covary across marine environments. However, little was known on the link of δ13CPOC and δ15NPN and the community and biochemical composition of phytoplankton. In this study, particulate organic carbon (POC) and nitrogen (PN), δ13CPOC, δ15NPN, phytoplankton community composition and biomass were determined during summer, along with environmental variables, in the shelf of the northern South China Sea influenced by the Pearl River plume, upwelling and anticyclonic eddy. Our results show that variability in δ13CPOC and δ15NPN along an environmental gradient is coupled with shifts in phytoplankton community composition and carbon to chlorophyll a (C:Chl a) ratio of phytoplankton. Low δ13CPOC values (−28.4 to −27.0‰) at nearshore stations (salinity <21) were primarily due to terrestrial POM input. High δ13CPOC (>−21.0‰) and δ15NPN (>5.6‰) values are most likely attributed to high abundance of diatoms induced by riverine nutrients in the plume‐impacted waters with intermediate salinity (21< salinity <33). Low δ13CPOC (<−22.0‰) and δ15NPN (−1.1–3.7‰) values are associated with high abundance of slow‐growing cyanobacteria in the oligotrophic area (salinity >33), where the lowest δ15NPN is most likely attributed to high abundance of N2‐fixing Trichodesmium spp., due to the influence of the anticyclonic eddy. Therefore, hydrodynamics modulates the biochemical composition and community composition of phytoplankton, leading to changes in δ13CPOC and δ15NPN. Our findings advance our understanding of the coupling of physical and biogeochemical processes in marginal seas.

Stable isotope spatial patterns for the Southwest Atlantic Ocean towards polar waters

Mapping stable isotope gradients (isoscapes) has become a powerful tool to understand and forecast the status and variability of marine ecosystems at different levels of ecological organization. To differentiate five marine areas from the Southwest Atlantic Ocean towards oceanic and polar waters, a key foraging area for many marine consumers, we built isoscapes at different spatial scales using carbon (δ13C) and nitrogen (δ15N) isotope values of phytoplankton, zooplankton and particulate organic matter in sediment. We analyzed the isotopic variability between marine areas in relation with oceanographic parameters (e.g. temperature, salinity) and geographical sampling site data (e.g. latitude, longitude). We collected samples during 6 oceanographic surveys conducted in spring and autumn between 2014 and 2019 at the Beagle Channel, the Atlantic coast of Tierra del Fuego and Burdwood Bank. We included also published isotopic data of zooplankton from two other oceanic areas (the Polar Frontal Zone and Polar Antarctic Peninsula waters) to construct large-scale isoscapes. We found that the marine areas analyzed have substantially different δ13C and δ15N baselines; some differences exist between spring and autumn but the general pattern of isotopic variability remains similar. Combining different biological components and spatial scale analysis, isotopic variability was found to be related to variables such as seawater temperature, depth, chlorophyll and nutrients. The generated data will enhance the efficacy of isoscapes in long-term monitoring initiatives that documents alterations in attributes and features across marine expanses. This is particularly pertinent to areas under legal protection, such as the oceanic Marine Protected Areas (MPAs) established in Argentine waters.

A comparative analysis of soil organic carbon stock and soil aggregation in two crop sequences in the Rolling Pampa (Argentina)

Understanding how farming practices affect soil organic carbon (SOC) accumulation is essential for sustainable agriculture. Agronomic decisions, such as crop sequence, significantly influence various soil properties. However, the overall benefits of crop rotation on soil structure and SOC storage remain uncertain. We compared the effects of soybean (Glycine max L.) monocropping with a three-year crop rotation comprising wheat (Triticum aestivum L.)/soybean double crop, maize (Zea mays L.), and soybean on the vertical distribution of SOC up to one metre depth. Additionally, we examined carbon accumulation as particulate organic matter-carbon (POM-C), soil aggregation, and structural stability in the topsoil. Compared to monocropping, crop rotation increased SOC concentrations (19 vs. 16 gC kg soil⁻¹), stock (12 vs. 10.7 MgC ha⁻¹), and POM-C content (6 vs. 3.2 gC kg soil⁻¹) in the first 5 cm of soil. At 20–65 cm depth, rotation showed a marginal increment of SOC stock with respect to soybean monocropping. The increased surface SOC content in the rotation positively affected the POM-C content and macro-aggregation. However, soil structural stability showed a tendency to be higher in the monocropping, especially at a depth of 5–20 cm. Overall, crop rotation demonstrated potential for enhanced carbon sequestration in temperate agroecosystems within three years, despite not significantly improving soil structural stability.

Quantitative evaluation of soil health based on a minimum dataset under various short-term crop rotations on the Canadian prairies

Maintaining and improving soil health (SH) is essential for the long-term sustainability and productivity of agriculture, notably in the face of climate change. This study addressed the challenge of selecting appropriate soil indicators, scoring methods, and indexing approaches for SH evaluation under no-till crop rotations. This study aimed to develop minimum datasets (MDS) and assess SH in six crop rotations (denoted as conventional, diversified, high-risk and high-reward, market-driven, pulse-oilseed intensified, and soil health-enhanced rotations) at three sites on the Canadian prairies. Fourteen soil indicators in the total dataset (TDS) were examined, encompassing both chemical (0–7.5 cm depth) and physical (5–10 cm depth) properties. Principal component analysis (PCA) identified MDSs from the TDS. Two scoring [linear (L) and non-linear (NL)] and two SH indexing approaches [additive (A) and weighted additive (WA)] were used to calculate the SH index (SHI). One-way ANOVA evaluated the SHI among crop rotations. The PCA revealed variations in the number of indicators in the MDS across sites, with soil organic carbon, bulk density, macroporosity, and plant-available water capacity as the common indicators for MDS across sites. Other indicators such as particulate organic matter carbon, aggregate stability, field capacity, and microporosity were found to be important, depending on the site. The non-linear weighted additive SH indexing (SHI.NLWA) proved to be the most sensitive and effective for differentiating among crop rotations in the short-term across study sites (R2 = 0.89–0.94, P < 0.05). Crop rotations significantly influenced SHI, with the diversified and high-risk and high-reward rotations having the highest SHI at Lethbridge and Scott, respectively. Overall, the diversified rotation at Lethbridge and Swift Current, along with the high-risk and high-reward rotation at Scott, exhibited better soil function than other rotations. Monitoring SHI over time and selecting crop rotations that improve SH can collectively enhance soil functions and agroecosystem productivity.

Source apportionment of suspended particulate organic matter in a shallow eutrophic lake of Southwest China using MixSIAR model

Eutrophication has become prominent in many lakes of the world, resulting in a continuous rise of suspended particulate organic matter (POM) that can be of vital consequence for water quality and carbon cycling. While the accumulation and decomposition of POM can enhance nutrient cycling at a rate depending on the property of lake-water organic carbon, it is important to identify the source of suspended POM for evaluating eutrophication and carbon burial. Here we analyzed the distribution of stable isotopic ratios (δ13C and δ15N) and the carbon/nitrogen ratio (C/N) in suspended POM in a shallow eutrophic lake of subtropical China, for apportioning the POM sources using Bayesian mixing model. Specifically, we collected seasonal samples of lake-water POM (>0.7 μm) from 20 sites in Yilong Lake from September 2020 to June 2022, as well as six types of modern samples covering the main carbon sources in the catchment. The spatial surveys showed that in the dry year (low water level) the δ13C of POM was more enriched in the western basin than those in the central and eastern basins, while the seasonal surveys showed the most enriched δ13C of POM in September. However, this spatio-temporal heterogeneity disappeared in the wet year (high water level). It was also found that the δ13C, δ15N and C/N values of POM varied significantly with those of phytoplankton across sites and seasons. Application of the MixSIAR model further showed that phytoplankton was the predominant source of POM in Yilong Lake (79.8 ± 13.4 %), but with large annual difference, 68.9 ± 10.3 % in the dry year and 90.7 ± 3.7 % in the wet year. In comparison, the contribution of the other five endmembers was much more moderate. In particular, the proportion of allochthonous organic carbon in POM was relatively low, with terrestrial plants and soils contributing 6.1 ± 4.8 % and 4.3 ± 2.5 % of POM, respectively. Our quantitative evidence for the dominance of the autochthonous source (i.e., phytoplankton) in lake-water POM over time and space suggested a determining role of eutrophication in the composition of lake organic carbon. Therefore, the coupling of algal blooms with organic carbon cycling in inland waters can be enhanced with continuous catchment development and regional warming.

Soil organic matter and aggregate stability dynamics under major no-till crop rotations on the Canadian prairies

There is a need to develop and adopt novel, more resilient, or “climate-smart” cropping strategies on the Canadian prairies, which are crucial for sustainable agroecosystem management. To examine how crop rotation influences soil organic matter and aggregate stability (AS) dynamics, six crop rotations: (i) conventional (control), (ii) pulse/oilseed intensified, (iii) diversified, (iv) market-driven, (v) high-risk and high-reward, and (vi) soil health-enhanced were established in 2018 at three field sites: Lethbridge, Alberta and Swift Current and Scott, Saskatchewan under no-till management. After 4-year, soil organic carbon (SOC), total nitrogen (TN), particulate organic matter carbon (POM-C) and nitrogen (POM-N), or mineral-associated organic matter C (MAOM-C) and N (MAOM-N) concentrations were not significantly affected by crop rotation in the 0–7.5 cm soil depth. However, crop rotation significantly altered AS at two of three sites, with both soil health-enhanced and high-risk and high-reward rotations having the highest AS at Lethbridge and Swift Current. Across all three sites, strong positive correlations were found among SOC, TN, MAOM, and AS. Moreover, MAOM-C and MAOM-N showed stronger relationships with AS than POM, perhaps suggesting a positive feedback loop on the stability of SOC and aggregation. Overall, the inclusion of pulses in rotations showed the potential to sustain soil quality, likely by offsetting low residue quantity with better residue quality and diversity, thereby supporting SOC accrual and AS similar to or greater than conventional cereal- or oilseed-dominated rotations.

Multiple nitrogen sources for primary production inferred fromδ13C andδ15N in the southern Sea of Japan

Abstract. Carbon and nitrogen dynamics in the Sea of Japan (SOJ) are rapidly changing. In this study, we investigated the carbon and nitrogen isotope ratios of particulate organic matter (δ13CPOM and δ15NPOM, respectively) at depths of ≤100 m in the southern part of the SOJ from 2016 to 2021. δ13CPOM and δ15NPOM exhibited multimodal distributions and were classified as belonging to four classes (I–IV) according to the Gaussian mixed model. A majority of the samples were classified as class II (n=441), with a mean ± standard deviation of δ13CPOM and δ15NPOM of -23.7±1.2 ‰ and 3.1 ± 1.2 ‰, respectively. Compared to class II, class I had significantly low δ15NPOM (-2.1±0.8 ‰, n=11), class III had low δ13CPOM (-27.1±1.0 ‰, n=21), and class IV had high δ13CPOM (-20.7±0.8 ‰, n=34). All the class I samples, whose δ15NPOM showed an outlier of total datasets, were collected in winter and had a comparable temperature and salinity originating in Japanese local rivers. The generalized linear model demonstrated that the temperature and chlorophyll-a concentration had positive effects on δ13CPOM, supporting the idea that the active photosynthesis and phytoplankton growth increased δ13CPOM. However, the fluctuation in δ15NPOM was attributed to the temperature and salinity rather than nitrate concentration, which suggested that the δ15N of source nitrogen for primary production is different among the water masses. These findings suggest that multiple nitrogen sources, including nitrates from the East China Sea, Kuroshio, and Japanese local rivers, contribute to the primary production in the SOJ.

The planktonic food web in the Gulf of Naples based on the analysis of carbon and nitrogen stable isotope ratios

AbstractPlankton play a key role in marine food webs by producing and transferring organic matter and energy to higher trophic levels. To define the trophic structure and interactions within the planktonic communities in the Gulf of Naples, we determined carbon and nitrogen stable isotope ratios in particulate organic matter (POM, &lt;20 μm), phytoplankton (20–200 μm), and bulk (unsorted) and sorted mesozooplankton (200–2000 μm) on a weekly basis in 2019. The stable isotope values of POM and, to a lesser extent, phytoplankton reflected the short‐term (weekly) alternation between offshore and coastal waters within seasonal variability. Although the isotopic signatures of coastal and offshore sources were still detectable in bulk mesozooplankton, δ13C and δ15N of single groups remained almost unchanged throughout the year. The trophic niches of mesozooplankton groups defined using the Stable Isotope Bayesian Ellipses in R software showed a high degree of overlap among them, which was corroborated by the tendency of most groups toward omnivory, beyond their known feeding habits, as indicated by MixSIAR models. Collectively, our results highlight that the complex network of interactions within the planktonic community in the Gulf of Naples can buffer natural variability due to the specific hydrographic features of the system. This characteristic makes the trophic structure of this community an ideal model for monitoring the response of planktonic food webs to climate‐ and anthropic‐driven changes.

Diversifying with grain legumes amplifies carbon in management-sensitive soil organic carbon pools on smallholder farms

Crop diversification with grain legumes has been advocated as a means to increase agroecological resilience, diversify livelihoods, boost household nutrition, and enhance soil health and fertility in cereal-based cropping systems in sub-Saharan Africa and around the world. Soil organic carbon (SOC) is a primary indicator of soil health and there is limited data regarding SOC pools and grain legume diversification on smallholder farms where soils are often marginal. In Malawi, a range of legume diversification options are under investigation, including rotations and a doubled-up legume rotation (DLR) system in which two compatible legumes are intercropped and then rotated with a cereal. The impact of the DLR system on SOC has not yet been determined, and there is a lack of evidence regarding SOC status over a gradient of simple to complex grain legume diversified systems. We address this knowledge gap by evaluating these systems in comparison to continuous sole maize (Zea mays L.) at three on-farm trial sites in central Malawi. After six years of trial establishment, we measured SOC in bulk soils and aggregate fractions and in faster cycling SOC pools that respond more rapidly to management practices, including water extractable organic carbon (WEOC), particulate organic matter carbon (POM-C), potentially mineralizable carbon (C), and macroaggregate C. Cropping treatment differences were not seen in bulk SOC or total N, but they were apparent in SOC pools with a shorter turnover time. The DLR system of intercropped pigeonpea (Cajanus cajan (L.) Millsp.) and groundnut (Arachis hypogaea L.) rotated with maize had higher WEOC, POM-C, potentially mineralizable C, macroaggregate and microaggregate C values than continuous maize. Of the single legume rotations, the pigeonpea-maize rotation had more mineralizable C and microaggregate C compared to continuous maize, while the groundnut-maize rotation had similar C values to the maize system. Overall, this study shows the potential for crop rotations diversified with grain legumes to enhance C in management sensitive SOC pools, and it is one of the first reports to show this effect on smallholder farm sites.

Long-term impact of manuring on soil organic matter quality indicators under field cropping systems

Introduction: Soil organic matter (SOM) quality is the major driving force for nutrient cycles impacting the productivity of cropping systems. Identification of sensitive indicators and developing metrics to assess SOM quality is a major challenge under field conditions.Methods: Data from a continuing long-term experiment since 2005 at Modipuram, India, were analyzed with key objectives to 1) observe the long-term effect of vermicompost/crop residues alone or in conjunction with NPK chemical fertilizers on crop yield and quality of SOM, 2) identify and develop SOM quality indicators (SOMQI) by encompassing sensitive indicators, and 3) predict system productivity by using SOMQI under rice (Oryza sativa L.)–potato (Solanum tuberosum L.)–wheat (Triticum aestivum L.) (RPW) and maize (Zea mays L.)–potato–onion (Allium cepa L.) (MPO) cropping systems. The treatments comprised of 100% NPK fertilizer; 100% N from vermicompost (N-VC); 50% NPK from fertilizer + 50% N from VC; 100% NPK from fertilizer + crop residue (CR); 100% N from VC + CR.Results: Results showed that continuous application of 100% N-VC and 100% N-VC+CR for eight years considerably increased the soil’s particulate organic matter carbon (POM-C), light fraction organic matter carbon (LFOM-C), and nitrogen (LFOM-N), dissolved organic carbon (DOC) and nitrogen (DON), as well as the available N (AN), available P (AP) and available S (AS) over control. Principal component analysis (PCA) identified AN, POM-C, LFOM-C: N, and DON in RPW and AN, POM-C, microbial biomass carbon (MBC), and LFOM-C: N in MPO cropping system as sensitive SOM quality indicators for the development of SOMQI. Under the MPO cropping system, results were more pronounced with 100% N-VC and 50% NPK+50% N-VC at 0–15 cm soil depth. Furthermore, at 15–30 cm depth, the effect was more prominent in 100% NPK + CR over other treatments.Discussion: Overall MPO cropping system exhibited better SOMQI than the RPW system. Rice, wheat, and maize yields increased significantly under different fertilizer treatments with organic or inorganic amendments. Substitution of fertilizer N with organic sources showed comparable yields obtained under 100% NPK treatment. Partial substitution of chemical fertilizers either by VC and/or CR enhanced the SOM quality and productivity under both cropping systems. The use of PCA-based SOMQI can be helpful in assessing SOM quality and predicting the productivity of cropping systems.

Limited impacts of occasional tillage on dry aggregate size distribution and soil carbon and nitrogen fractions in semi-arid drylands

Tillage management that minimizes the frequency and intensity of soil disturbance can increase soil carbon (C) and nitrogen (N) sequestration and improve the resilience of dryland cropping systems, yet the impact of occasional disturbance on soil aggregate formation and the soil organic carbon (SOC) storage within aggregates has not been studied well. We evaluated the effect of four tillage management practices on soil dry aggregate size distribution, aggregate-protected C and N, mineral-associated organic matter carbon (MAOM-C), particulate organic matter carbon (POM-C), and corn (Zea mays L.) and sorghum (Sorghum bicolor (L.) Moench) yields in a semi-arid dryland cropping system. Treatments included conventional tillage (CT), strip-tillage (ST), no-tillage (NT), and occasional tillage (OT) management in a corn-sorghum rotation. Soil macro-aggregates were 51–54% greater under ST, NT, and OT, while small and micro-aggregates were greater in CT. Conventional tillage reduced soil aggregate-associated C by 28–31% in macro-aggregates and 47–53% in small aggregates at 26 months (M) sampling compared to ST, NT, and OT. In clay + silt fraction, CT had 14–16%, 21–26%, and 36–43% less SOC at 7, 14, and 26M samplings, respectively, than ST, NT, and OT. Aggregate associated N was generally similar under ST, NT, and OT, which was greater on average than CT. Soil MOAM-C and POM-C under ST, NT, and OT were generally greater than respective SOC fractions under CT at 19 and 26 M after OT implementation. Corn and sorghum yields were similar among tillage systems in 2020, but greater under ST, NT, and OT than CT in 2021. Our results suggest that while frequent intensive tillage can lower SOC and N storage, a single stubble mulch occasional tillage after several years of NT does not lead to soil C and N losses and soil structural instability in semi-arid drylands.

Rapid increase of surface water pCO2 revealed by settling particulate organic matter carbon isotope time series during 2001–2009 in Sagami Bay, Japan

Rapid increase of surface water pCO2 revealed by settling particulate organic matter carbon isotope time series during 2001–2009 in Sagami Bay, Japan

ESTOQUES DE CARBONO DO SOLO E COMPARTIMENTOS DA MATÉRIA ORGÂNICA SOB SISTEMAS CONVENCIONAIS NO SEMIÁRIDO BRASILEIRO

ABSTRACT The objective of this study was to evaluate the effect of the conversion of secondary native vegetation (NV) to conventional systems (agriculture and pasture) in soil organic carbon (SOC) and carbon of fractions particulate organic matter (POM) and mineral-associated organic matter (MAOM) in the Brazilian semi-arid region. The study was carried out in the municipalities of Delmiro Gouveia, Inhapi and Pariconha, in Alagoas, Brazil. Soils were collected in the layers of 0-0.1, 0.1-0.2 and 0.2-0.3 m. The treatments analyzed were: agricultural crops with 4, 15 and 30 years and pasture with 10 years. As a reference, the secondary Caatinga was used. The results show that in soils with sandy texture (Neossolos Quartzarênico and Regolítico – Arenosols and Regosols, respectively), there were reductions in SOC levels and carbon in the compartment associated with minerals. The inverse can be observed in the clay-textured Argissolo (Acrisols), with 30 years of cultivation, in which there was an increase in SOC and C in the quantitative fractions of soil organic matter. In addition, despite the sandy texture of the Neossolo Regolítico, POM levels were increased in the pasture system in comparison to native vegetation, but it was not enough to recover the original SOC content of this system.

Does the accretion of carbon fractions and their stratification vary widely with soil orders? A case‐study of an Alfisol and an Entisol of sub‐tropical eastern India

AbstractComparison of the carbon (C) stocks among different soil orders allows us to explore the role of various soil characteristics in long‐term C storage and their vulnerabilities. This study quantified and compared the accumulation rates of soil organic carbon (SOC) fractions (in 0–60 cm soil profile) in an Alfisol of Malda (25°27′33.9″N, 88°19′10.2″E) and an Entisol of Cooch Behar (26°09′62.7″N, 89°53′51.7″E) districts of West Bengal, India. We noticed a greater level of SOC (0–60 cm depth) in the Alfisol than the Entisol as the former soils were clayey in nature (fine textured) which provided the maximum stabilization of SOC compared to the Entisol (sandy textured). However, the storage of C fractions showed some peculiar results. The concentration of mineral‐associated carbon (Min‐C) was more or less similar in both the soil orders, but its stock was maximum in the Alfisol. While in the Entisol, permanganate oxidizable carbon (POX‐C) and particulate organic matter carbon (POM‐C) stocks recorded maximum among all the studied depths. A positive relation of SOC fractions and stocks with clay (r2 = &gt;0.500 in the Alfisol; r2 = &gt;0.700 in the Entisol) indicated the importance of finer fractions in profile storage of C. Min‐C contributed to SOC of about 75%–85% followed by POM‐C (3.27%–17.87%) and POX‐C (2.57%–4.22%). Higher stratification of SOC and POX‐C and POM‐C fractions was observed in Entisol; while in Alfisol, stratification of Min‐C was greater. Overall, this research demonstrated that the Alfisol has a greater potential in stabilizing Min‐C than the Entisol with POM‐C and POX‐C and the distribution of these fractions varied as per its stabilization.

Sources and Distribution of Organic Matter in Coastal Area of Muang Chonburi District, Eastern Thailand: Using Carbon and Nitrogen Stable Isotopes

The sources and spatial distribution of organic matter were investigated in the nearshore area receiving untreated urban wastewater and offshore areas containing bivalve mariculture in Muang Chonburi District. Content, elemental, carbon, and nitrogen isotopic analyses in particulate organic matter (POM) and surface sediments were performed. We found particulate organic carbon (POC), δ13C, and δ15N of POM ranging from 435.0-5,247.7 µg/L, -27.7 to -22.0 ‰, and 1.7-8.6 ‰, respectively, whereas total organic carbon (TOC), total nitrogen (TN), δ13C and δ15N in sediment were 3.5-76.9 µg/g, 0.8-8.3 µg/g, -25.7 to -22.9 ‰ and 2.6-6.0 ‰, respectively. These values show significant differences between nearshore and offshore sampling stations wherein accumulation of organic matter was high in the nearshore and decreased with greater distance offshore, with some retained in the bivalve farming area. The results from a mixing model indicated that organic matter in POM and sediment were initially derived from anthropogenic organic matter. In contrast to the offshore water which had organic matter derived from marine organic matter. This study highlights the distribution of anthropogenic organic waste released to coastal waters with plenty of bivalve farms such as green mussels and oysters. The results can be used to advise national strategies regarding bivalve aquaculture zoning and seafood safety policies going forward.

An Original Experimental Design to Quantify and Model Net Mineralization of Organic Nitrogen in the Field

Improving the assessment and prediction of soil organic nitrogen (N) mineralization is essential: it contributes significantly to the N nutrition of crops and remains a major economic and environmental challenge. Consequently, a network of 137 fields was established in Brittany, France, to represent the wide diversity of soils and cultivation practices in this region. The experimental design was developed to measure net N mineralization for three consecutive years, in order to improve the accuracy of measuring it. Net N mineralization was quantified by the mineral N mass balance, which was estimated from March to October for a maize crop with no N fertilization. The effect of climate on mineralization was considered by calculating normalized time (ndays) and, then, calculating the N mineralization rate (Vn) as the ratio of the mineral N mass balance to normalized time. Strict screening of the experimental data, using agronomic and statistical criteria, resulted in the selection of a subset of 67 fields for data analysis. Mean Vn was relatively high (0.99 kg N ha−1 nday−1) over the period and varied greatly, from 0.62 to 1.46 kg N ha−1 nday−1 for the 10th and 90th percentiles, respectively. The upper soil layer (0–30 cm) was sampled to estimate its physical and chemical properties, particulate organic matter carbon and N fractions (POM-C and POM-N, respectively), soil microbial biomass (SMB), and extractable organic N (EON) determined in a phosphate borate extractant. The strongest correlations between Vn and these variables were observed with EON (r = 0.47), SMB (r = 0.45), POM-N (r = 0.43), and, to a lesser extent, the soil N stock (r = 0.31). Vn was also strongly correlated with a cropping system indicator (r = 0.39). A modeling approach, using generalized additive models, was used to identify and rank the variables with the greatest ability to predict net N mineralization.

Stable and unstable carbon fraction under different vegetable farming system on Mt. Merbabu’s andisols, Central Java

This study aims to find out the effect of vegetable cultivation systems that are managed organically, semi-organic, and conventionally on the unstable and stable carbon fraction of Andisol soil on the north slope of Merbabu. Field research was carried out using a sampling method in 3 different farming systems, namely organic (O), semi-organic (SO), and conventional (K) and 3 soil depths, namely 0-20 cm, 20-40 cm, and 40-60 cm. The parameters measured include the physical, chemical, and biological properties of the soil. The physicochemical properties of the soil analyzed included texture, volume weight of soil, pH-H2O, pH-NaF, organic matter, cation exchange capacity, total-N, Al/Fe extracted oxalate and pyrophosphate. The carbon fractions analyzed included particulate organic matter carbon, water-soluble carbon, soil organic carbon mineralization, microbial biomass carbon, humic acid, and fulvic acid. Analysis of Variance (ANOVA) was conducted to determine the effect of farming system and soil depth on soil physicochemical properties, while the difference between the two-treatment means was analyzed by DMRT. Regression-correlation analysis was carried out to determine the close relationship between the independent and dependent variables. The results showed that the farming system and soil depth had a significant effect on soil physical and chemical properties. Parameters of soil chemical properties that significantly affect the farming system and soil depth are pH-H2O, pH NaF, organic matter, cation exchange capacity, total-N, and Al/Fe pyrophosphate extracted. Organic farming systems have an unstable and stable organic carbon fraction that is more dominant than semi-organic and conventional farming systems. Parameters of soil chemical properties such as organic matter, total organic carbon, and total-N are closely related to particulate organic matter carbon, water-soluble carbon, microbial biomass carbon, soil organic carbon mineralization, soil humic and fulvic acid. The organic farming system has been proven to improve the physical and chemical properties of the soil and increasing the availability of organic carbon fraction in Andisol soil.

Composition of Particulate Matter Emitted from Lean Burn Gas Engine with Pre-chamber Spark-plug Ignition System and Comparing Emissions with Those from Diesel Engines

When investigating the sources of particulate matter (PM) and its reduction methods, it is important to clarify its composition. In this study, PM emitted from a lean burn gas engine with a pre-chamber spark plug ignition system was analyzed by quantifying emission factors of PM components, namely Elemental Carbon (EC), Organic Carbon (OC), sulfate and nitrate, as well as “the other components” . These emission factors were compared with previous results of PM constituents emitted from diesel engines in an attempt to gauge how this gas engine could contribute to reducing PM emissions. At 75% engine load, the percentages of EC, OC, sulfate and nitrate in PM were less than 3%, 70%, less than 1% and 10% respectively with the other components being the remaining 18%. The low proportion of EC was caused by lean fuel conditions inside the gas engine. OC, which accounted for a majority of PM, is thought to have derived from vaporized lubricant oil. A slight amount of sulfur may have originated in either sulfur contents in lubricant oil or odorous components in city gas. At any engine load, the gas engine’s PM emissions were more than 70% lower than those from diesel engines. Two-thirds of reductions in PM emissions came from EC and the remaining one-third were due to a drop in emissions of the other components.

Characteristics of emission and light-absorption of size-segregated carbonaceous aerosol emitted from four types of coal combustion at different combustion temperatures

Coal consumed in domestic cooking and heating in rural areas of China is considered as a major source of air pollution. To efficiently represent the emission of coal burnt for residential living at various combustion regimes, four coal samples are selected for combustion experiments in the simulated air state at three different temperatures in a drop-tube furnace system in this study. Size-segregated particulate matter in flue gas from combustion of the four coal samples at different temperatures were collected by a TISCH-type Andersen eight-stage impact sampler operating synchronously with the furnace system. The emission factors of the particulate matter samples show that OC2 and OC3 are the main carbonaceous products of bituminous coal and lignite combustion. It is also found that the particulate matter from lignite flue gas contains EC1 in a large proportion and a small amount of highly-refractory EC2 and EC3 from bituminous coals. Meanwhile, in order to evaluate the light-absorption of organic carbon in particulate matter, the mass absorption cross efficiency (α/ρ) is investigated. The clear-sky radiative transfer model shows that BrC emitted from low-temperature burning leads to even positive top-of-atmosphere radiative forcing at surfaces with an albedo of 0.19. In the 300–700 nm spectral band, the simple forcing efficiency (SFE) of particulate matter sampled significantly decreases as combustion temperature and coal maturity increase. The particulate matter presents a high SFE in the range of 0.4–1.1 μm in terms of particle size.

Response of soil carbon fractions in a Haplic Cambisol to crop rotation systems and residue management practices under no tillage in the Eastern Cape, South Africa

Soil organic carbon (SOC) is a major indicator of soil quality and/or health but its slow short-term response to management changes has prompted the search for more sensitive indicators for monitoring short-term changes in soil organic matter (SOM). This study aimed to investigate the short-term effects of crop rotation systems and residue management practices under no tillage on selected soil carbon fractions of a Haplic Cambisol, using plots from a conservation agriculture (CA) field trial (split plot design replicated in three blocks). The main plots were comprised of the crop rotation systems: maize-fallow-maize (MFM), maize-fallow-soybean (MFS), maize-wheat-maize (MWM) and maize-wheat-soybean (MWS). Residue management practices that included residue removal (R−) and residue retention (R+) were allocated to the sub-plots. The carbon fractions measured were SOC, microbial biomass carbon (MBC), mineralisable carbon (Cmin) and particulate organic matter carbon fractions (POM-C). Crop rotation systems significantly (p < 0.05) influenced Cmin and POM-C fractions whereas residue management practices significantly (p < 0.05) affected all the carbon fractions. Crop residue retention as opposed to its removal enhanced all the carbon pools. The POM-C and Cmin fractions were more sensitive to short-term CA management interventions than SOC and MBC, therefore they can be used for monitoring SOM changes and microbial activities.