Humin Fraction Research Articles

Changes in Soil Humin Macromolecular Structure Resulting from Long-Term Catch Cropping.

The aim of this study was to assess the effect of long-term catch crop application on the structural properties of humin, which is considered the most recalcitrant fraction of soil organic matter. Soil samples from a 30-year field experiment on triticale cultivated with and without catch crops were analysed to determine the total organic carbon content and fractional composition of humic substances. Meanwhile, humin isolated from bulk soil was analysed to determine its elemental composition and spectroscopic properties measured with UV-Vis, fluorescence, and 13C-CPMAS-NMR. It was found that catch crop farming enhanced the formation of highly reactive humus substances, like low-molecular-weight fractions and humic acids, while decreasing the humin fraction. The higher H/C and O/C atomic ratios of humin and the UV-Vis, fluorescence, and 13C-CPMAS-NMR results confirmed a higher share of oxygen-containing functional groups in humin isolated from the soil with catch crop rotation, also corroborating its greater aliphatic nature. Under the conditions of our field experiment, the results indicated that organic residues from catch crops quickly undergo the decay process and are transformed mainly into highly reactive humus substances, which can potentially improve soil health, while mineral fertilisation alone without catch crops favours the stabilisation and sequestration of carbon.

Carbon stocks in Planosols along a rainfall gradient in Northeast Brazil

Planosols have sandy-textured surface horizons that abruptly cover a dense subsoil with high clay content, which usually limits drainage and influences soil moisture. Here, we investigated changes in C storage through the pedogenic horizons of soil profile, including detailed sampling of A and B horizons along a transect to cover rainfall variation (584–1130 mm year−1) and soil cover of Planosols, including dry land areas in Northeast Brazil. The soil profile located under highest precipitation and with the greatest pedogenic development (150 cm) showed the largest C stock (101.91 Mg/ha), surpassing estimates of other soil classes. In addition, our results suggest that soil cover and pedogenesis impact C storage in Planosols. An average of 64 % of C is stored in subsurface horizons that present abundant clay fraction; thus, the dynamics of subsurface soil organic carbon (SOC) appear to be more controlled by soil features than by climate. Values of δ13C indicated the predominance of C3 plant, except in area with sugarcane cultivation (C4 plant). Changes in C distribution within the horizon suggest changes in degree of decomposability of soil organic matter (SOM), mainly in A1 and B1 layers, with A horizon richer in labile compounds. δ15N values indicated that N dynamics differ in the gradient. The thermal analyses showed that around 70 % or more of humin fraction is composed of structures more resistant to degradation, suggesting that C stock in Planosols has relative stability. However, in driest part of the climate transect, SOM may be more vulnerable to losses due to the large relative quantity of aliphatic groups in soil surface and subsurface. This work provides insights into the mechanisms the determine C storage distribution in tropical Planosols and contributes to appropriate use and management of these soils to ensure the valuable ecosystem service of C storage.

Effect of soil management on carbon stock and soil aggregation in an area of natural regeneration and surrounding systems in the Atlantic Forest biome

This study aimed to quantify total organic carbon (TOC), carbon of humic substances (HS), and their stocks and evaluate the soil structural stability of areas with different uses under sandy loam soil texture. Soil samples were collected from managed areas and a reference area: Permanent Pasture (PP), No-Till (NT), Private Natural Heritage Reserve in the process of natural regeneration (PNHR) and Native Forest (FN). Dry mass analysis, carbon stock quantification, chemical fractionation of soil organic matter and soil aggregation were carried out. The NF area had the highest deposition of litter mass (ML). The PP and NT areas had the highest bulk density (Bd). TOC and Stock-C contents were higher in PNHR, followed by NF, and stratification index (STRATI) was also higher in the regeneration area. The NT, PNHR, and NF areas had a higher proportion of carbon fulvic acid fraction (C-FA) than carbon humic acid fraction (C-HA), but the fraction with the highest representation in all areas was carbon humin fraction (C-HUM). The PP, PNHR, and NF areas obtained the best aggregate stability indicators, as well as a higher proportion of macroaggregates, with the NT area having low aggregate stability. Recovery of C contents was observed in recent years in the area of PNHR, leading to a greater storage of C, which shows a quantitative recovery of C in the soil in this area after four years of natural regeneration. Furthermore, the PP and NT areas present a lower capacity for C sequestration, mainly due to the management conditions. Keywords: aggregate stability, climate change, crop production, soil quality.

The Effects of the Interaction of Pesticides with Humin Fraction as Influencing the Sustainable Development of Agroecosystems

Humin (HUM) is the most stable fraction of the soil organic matter, whose properties determine the soil health and sustainable development of agroecosystems. The aim of the paper was to determine changes in the properties of the HUM after interaction with selected pesticides, which can be visualized using photoluminescence methods. The HUM was isolated from the mollic horizon of Phaeozems arable soils derived from different parent materials in Poland. The isolated and purified HUM were saturated in a batch experiment with selected herbicides and insecticides, then analyzed for chemical composition and spectroscopic properties: Electron Paramagnetic Resonance, fluorescence, and delayed luminescence. The research showed that the interaction of the HUM with selected pesticides caused significant changes in the elemental composition of the HUM; however, no changes in their aromaticity/aliphaticity were found. The impact of pesticides was also marked by a reduction in the concentration of radicals, fluorescence and delayed luminescence intensity and properties. Changes in spectroscopic characteristics and their relationship with soil organic matter (SOM) structure properties require further research so that their results can be used in the management of agroecosystems in accordance with the principles of sustainable development.

Mineralization and residue characteristics of chloramphenicol in aerobic soils: evidence from a carbon-14 study.

Chloramphenicol, a broad-spectrum antibiotic employed for controlling bacterial infections, presents an intriguing aspect in terms of its environmental fate in soils. 14C-labeled chloramphenicol was used to explore its mineralization and residue characteristics in three distinct agricultural soils in China. The findings revealed a nuanced pattern in the fate of 14C-chloramphenicol, with notable variations among the different soils under investigation. The chloramphenicol extract residue exhibited a reduction of 18.04% in sandy clay soil, 23.04% in clay loam soil, and 21.73% in loamy clay soil. Notably, the mineralization rate in sandy clay soil was 25.22% surpassed that in the other two soils, particularly during the initial stages of incubation. Over time, the diminishing extract residue underwent conversion into minerals and bound residue. The formation rate of bound residue was increased from 44.59 to 53.65% after adding 10% manure, suggesting that chloramphenicol easily binds with soils rich in organic matter. The bound residue is predominantly localized in the humin fraction across all soils. Additionally, the sterilized soil experiments indicated the pivotal role of microorganisms in influencing the fate of chloramphenicol under the specified experimental conditions. In conclusion, this study offers valuable insights into the environmental dynamics of chloramphenicol in soils, emphasizing the importance of soil composition, organic matter content, and microbial activity. The findings contribute to a scientific understanding of the environmental safety implications associated with chloramphenicol usage.

HORIZONTAL WATERMILL CHRONOLOGIES BASED ON 14C DATING OF ORGANICS IN MORTARS: A CASE STUDY FROM JARASH, JORDAN

ABSTRACTHorizontal watermills in the southern Levant have proved difficult to date. This study investigates the use of radiocarbon (14C) dating of various organic carbon fractions in structural mortars and carbonate deposits to identify terminus post quem (TPQ) construction dates for seven arubah watermills and two chute watermills in northern Jordan. Dating results from the various organic fractions are discussed in the contexts of carbon fraction integrity and mortar type. The arubah watermill construction dates fall into two chronological groups. Four arubah watermills have Middle Islamic (late 12th to early 14th century AD) construction dates based on macrocharcoal and bulk organic fraction ages, whereas the bulk organic fraction ages of two earlier arubah watermills straddle the Byzantine-Early Islamic transition. Their possible fifth to seventh-century construction dates are among the earliest in the southern Levant. Limited 14C data from the chute water mills suggests that the earliest may date to the sixth–seventh century period, concurrent with the older arubah watermills. The study supports the viability of the AMS 14C method to provide estimated TPQ construction dates for watermills, providing caution is exercised. Short-lived macrocharcoals have the highest integrity but are subject to severe sample loss during pretreatment. 14C ages from humic and humin fractions in earthen mortars are influenced by “old carbon” contamination, possibly a soil reservoir effect, and are centuries older than the probable construction date. Attention is drawn to the potential use of arubah carbonate deposits as proxy records of water flow, watermill use, and hydroclimate.

THE INFLUENCE OF PLANT SPECIES AND PRETREATMENT ON THE 14C AGE OF CAREX-DOMINATED PEAT PLANTS OF A PEAT CORE FROM JINCHUAN MIRE, NE CHINA

ABSTRACT The comparisons among 126 14C dates of Carex samples including separated leaf and root parts with acid (A)-treatment and acid-base-acid (ABA)-treatment, and 48 published 14C dates of bulk peat plants on a 92-cm core from Jinchuan Mire in NE China, indicate old carbon influence (OCI) on the 14C dates. The OCI varies with plant species, pretreatment and peat depth. In vascular peat plants such as Carex, humin fractions (remains after ABA treatment) and humic acids are representative of the original plant precursor, while fulvic acids are regarded as the secondary mobile product which should be removed for 14C dating. ABA- treatment removes both fulvic acids and humic acids, whereas A-treatment gets rid of only fulvic acids. Carex roots uptake more dissolved CO2 in peat water. Carex leaves may use more CO2 (involving degassing CO2) above the peat surface. By removing humic acids throughout ABA treatment, the OCI may vary differently over depth (time). ABA treatment cannot eliminate the fixed OCI in humin fractions of vascular peat plants, instead, this treatment may enhance OCI by removing humic acid which may represent the true age of the plants. In addition, Bacon model results on this core could not show rapid changes in accumulation rate.

Effects of Long-Term Management on Soil Organic Carbon in Tropical Peatlands

Objective: The aim of this study was to evaluate the effects of Histosols management on soil organic matter (SOM) characteristics. Theoretical framework: Histosols are soils that provide ecosystem services, especially carbon stocks. Among the environments in which these soils are formed, peatlands stand out. The conversion of these areas into agricultural systems requires soil drainage. This practice causes reductions in carbon content and changes in the structure of the SOM. Methodology: The study was conducted in the municipality of Rio de Janeiro, Brazil. The soils were classified as Histosols. Three areas were selected: a) cassava (Manihot esculenta) cultivation for 80 years; b) forest fragment for 20 years; c) consortium of coconut palm (Cocos nucifera) and cassava for 20 years. Total organic carbon (TOC); particulate organic carbon (COP); organic carbon associated with minerals (COam); fulvic acid fraction carbon (CAF); humic acid fraction carbon (CAH) and; humin fraction carbon (CHUM) were determined. Solid-state spectroscopy (UV-vis, ATR-FTIR and 13C NMR CP/MAS) was carried out to characterize the structure of the SOM. Results and conclusion: The results showed that management and drainage have an impact on the TOC content, fractions and chemical structure of the SOM. The management adopted in the cassava area had an impact on the labile and humified fractions of the SOM. Spectroscopy showed that labile structures were lost in the humic acids (HA), while in the forest area only recalcitrant structures were preserved. Research implications: The conversion of Histosols to agricultural production using the drainage technique promotes quantitative and qualitative changes in SOM in the long term. In order to reduce greenhouse gas emissions, it is necessary to use techniques that promote carbon stocks in the soil. Originality/value: This study uses spectroscopic and chemometric techniques to highlight the effects of long-term soil management on the chemical structure of the SOM and to quantify the total carbon content and SOM fractions.

Impact of Diverse Agricultural Land Uses on Soil Organic Matter Fractions: A Comprehensive Evaluation

Organic matter is a crucial component of soil that influences various soil properties and functions, including nutrient cycling, soil structure, water holding capacity and microbial activity. Different agricultural land uses significantly influence the quantity and quality of soil organic matter (SOM) fractions. The primary constituent of SOM is humic substances, also known as humus. These are stable compounds originating from the decomposition of organic matter derived from plants, animals, and microorganisms. The soil humic fraction is categorized into humic acid (HA), fulvic acid (FA) and humin (HN) based on the solubility in acid and alkaline medium. The structural arrangement, chemical constitution and stability of the humic substances in soil are affected by various factors, including climate, parent material, altitude, vegetation and the management practices employed in the area. In this context the present study was proposed to assess the impact of various agricultural land use systems on humic acid, fulvic acid and humin fraction in soils of different agro-ecological units (AEUs) of southern Kerala. The study focused on specific AEUs in southern Kerala, including the southern coastal plain (AEU 1), Onattukara sandy plain (AEU 3), southern laterites (AEU 8), south central laterites (AEU 9) and southern and central foothills (AEU 12). Within each AEU, various agricultural land use categories such as, coconut, rice, rubber and uncultivated land were selected as specific focal points for this investigation. The HA, FA and HN content in soil exhibited varying ranges across different AEUs, ranging from 0.57 to 2.06, 0.73 to 2.33, and 0.62 to 1.59 per cent respectively. Among the various land uses, rubber exhibited significantly higher levels of HA (1.72%), FA (2.01%) and HN (1.44%) compared to coconut, rice and uncultivated land. Among the different organic matter fractions, FA (32.30-36.18 %) contributed more towards SOM than HA (29.40-32.51 %) and HN (26.43-29.25 %).

Soil and litter properties from a riparian to non-riparian zone in a tropical dry forest

Riparian zones of dry tropical forests are important due to their effect on nutrient cycling and carbon dynamics. It’s important to evaluate the changes that occur when these areas are altered, in order to ascertain the magnitude of nutrient gains or losses. This work evaluates chemical changes in soil and litter transitioning from a riparian to a non-riparian zone. Plots were established for soil and litter sampling in riparian and non-riparian zones. For chemical analysis, litter and soil surface sampling were performed at depths of 0.0 to 0.10 m and 0.10 to 0.20 m. The descriptive and principal component analysis assessed chemical attribute sets' soil and litter characteristics. We observed higher P, K, and Ca content at both depths in soils of the non-riparian zone. The total soil organic carbon content in the non-riparian zones was 1.28 and 1.51 times greater at 0-10 and 10-20 cm depths, respectively than in the riparian zones. This study revealed that despite the chemical and organic inputs in the non-riparian zones, no significant differences were observed regarding the chemical properties of the soils of riparian areas as opposed to the soils of non-riparian areas since the litter of the riparian zones was richer in nutrients. Additionally, this study suggests that the humic acid and humin fractions are responsible for maintaining fertility in riparian areas due to strong correlations with soil nutrients.

Sorption of pendimethalin by humin fraction isolated from Mollic horizon of Chernozems

Sorption of pendimethalin by humin fraction isolated from Mollic horizon of Chernozems

Chemical and Spectroscopic Characteristics of Humic Acids Under No-Tillage and Forest Systems

ABSTRACT This study aims to evaluate the no-tillage system (NT) with different implantation times and vegetation cover on changes in the chemical and structural compositions of soil humified organic matter. Five areas with different NT management histories were studied; for 6 (NT6), 14 (NT14), 22 (NT22) years with succession of soybean/corn crops; for 12 years and 4 more years with corn and Brachiaria (NT+B), pasture for 39 years and native forest. Soil samples were collected at the depths of 0.0–0.05 and 0.05–0.10 m. The changes in the quality of humic acid (HA) were evaluated by several chemical techniques (total organic carbon (TOC), fulvic acid fraction (FA), humic acid fraction (HA) and humin fraction (HU), ionizable functional groups, elemental composition) and spectroscopic techniques (UV–Vis absorption, fluorescence, and Fourier transform mid-infrared photoacoustic spectroscopy, called FTIR-PAS). On the surface, the TOC, carbon of the HA and HU fractions, total acidity, phenolic acidity, Carbon, Nitrogen, Sulfur, Hydrogen and Hydrogen/Carbon ratio were higher in the areas of forest, pasture and NT22. On the subsurface, the responses are the same as on the surface. However, the NT22 system presents higher FA, HA, carboxylic acidity and humification degree (HD). UV–Vis absorption spectroscopy, fluorescence spectroscopy and FTIR-PAS can discriminate soils under different managements and under natural conditions. Agronomic practices have strongly affected the soil organic matter, in which the NT promotes the formation of HA with characteristics closer to those of the forest, as the implantation time increases, such as 22-year-old NT and pasture. This indicates that care must be taken in managing the no-till system to maximize its potential to promote stabilization of organic matter, thereby contributing to carbon sequestration.

The Interaction of Pesticides with Humin Fractions and Their Potential Impact on Non-Extractable Residue Formation.

The constant influx of pesticides into soils is a key environmental issue in terms of their potential retention in the soil, thus reducing their negative impact on the environment. Soil organic matter (SOM) is an important factor influencing the environmental fate of these substances. Therefore, the aim of this research was to assess the chemical behavior of pesticides (flufenacet, pendimethalin, α-cypermethrin, metazachlor, acetamiprid) toward stable soil humin fractions (HNs) as a main factor affecting the formation of non-extractable residues of agrochemicals in soil. This research was conducted as a batch experiment according to OECD Guideline 106. For this purpose, HNs were isolated from eight soils with different physicochemical properties (clay content = 16-47%, pHKCl = 5.6-7.7, TOC = 13.3-49.7 g·kg-1, TN = 1.06-2.90 g·kg-1, TOC/TN = 11.4-13.7) to reflect the various processes of their formation. The extraction was carried out through the sequential separation of humic acids with 0.1 M NaOH, and then the digestion of the remaining mineral fraction with 10% HF/HCl. The pesticide concentrations were detected using GC-MS/MS. The pesticides were characterized based on the different sorption rates to HNs, according to the overall trend: metazachlor (95% of absorbed compound) > acetamiprid (94% of absorbed compound) > cypermethrin (63% of partitioning compound) > flufenacet (39% of partitioning compound) > pendimethalin (28% of partitioning compound). Cypermethrin and metazachlor exhibited the highest saturation dynamic, while the other agrochemicals were much more slowly attracted by the HNs. The obtained sorption kinetic data were congruous to the pseudo-first-order and pseudo-second-order models related to the surface adsorption and interparticle diffusion isotherm. The conducted research showed that the processes of pesticide sorption, apart from physicochemical phenomena, are also affected by the properties of the pollutants themselves (polarity, KOC) and the soil properties (SOM content, clay content, and pHKCl).

Soil management effects on soil organic matter properties and carbon sequestration (SOMPACS)

SOMPACS is a project recommended by EJP SOIL for funding under the 1st External Call "Towards Healthy, Resilient and Sustainable Agricultural Soils". The goal of this project is to assess management practices that enrich organic matter pools that are resilient to rapid microbial decomposition. The project started in 2022 as a consortium of 12 research institutions from Poland, Germany, Ireland, Lithuania, UK, Italy and USA for a period of three years. Soil and vegetation samples from eight long-term experiments that differ in soil management practices (i.e., conventional vs. no-tillage; mineral vs. organic fertilization; with and without catch crop; and arable land vs. undisturbed grassland) are investigated. Study sites include: 22- and 54-year long experiments in Lithuania; 26-year long experiment in Italy; 30- and 40-year long experiments in Ireland; 30- and 46- and 100-year long experiments in Poland; and 178-year long Broadbalk experiment in Great Britain. Additional experimentation includes assessing the impact of root growth promoting amendments (commercially available humic substances, biochar and biogas digestate) on stable organic matter pools. In parallel with soil sampling, plant productivity are measured in all field experiments. This investigation is couples fields studies with small-scale experimental plots and laboratory incubations under controlled conditions. In addition to assessing basic soil properties, the following state-of-the-art analyses are conducted: SOM composition and stability by Py-GC-MS; fractionation of aggregate size classes and C pools of increasing physicochemical protection; isotopic analysis of δ13C and δ15N performed on different SOM pools; microbiological properties (community-level physiological profiling, selected functional genes involved in C and N cycles, microbiome and mycobiome analyses by next-generation sequencing, genetic diversity using terminal restriction fragment length polymorphism); enzymatic activity; soil water retention and soil water repellency; mineral composition of clay fraction; (8) soil structure stability. SOM composition and stability by Py-GC-MS; fractionation of aggregate size classes and C pools of increasing physicochemical protection; isotopic analysis of δ13C and δ15N performed on different SOM pools; microbiological properties (community-level physiological profiling, selected functional genes involved in C and N cycles, microbiome and mycobiome analyses by next-generation sequencing, genetic diversity using terminal restriction fragment length polymorphism); enzymatic activity; soil water retention and soil water repellency; mineral composition of clay fraction; (8) soil structure stability. The most resistant SOM pool (humin) are isolated by different methods (isolation vs. extraction) and examined for chemical composition and structure, using spectrometric and spectroscopic techniques (mass spectrometry, NMR, FTIR, EPR, UV-Vis-NIR, fluorescence). The carbon stocks in the soil profile will be evaluated and the carbon extractable in cold water will be determined to assess the potential carbon leaching and microbial availability. Additionally, in-field soil carbon dioxide (CO2) fluxes from selected experiments is monitored. Thus far, soil samples (0-100 cm depth) were collected and the humin fraction from surface A horizon was isolated for spectroscopic studies. Crop yield and vegetation productivity was also assessed. The research was financed by NCBR (EJPSOIL/I/78/SOMPACS/2022).

Soil chemical attributes under west indian cherry fertigated with nitrogen and humic substances

The use of humic substances (HS) in the soil can increase the efficiency of nitrogen fertilizers and contribute to the increment in soil organic matter and plant nutrient availability. Hence, this study aimed to evaluate, in two production cycles, the effect of applying HS and different nitrogen (N) doses on the chemical attributes and organic matter fractions of a soil cultivated with West Indian cherry in the Brazilian semiarid region. The experiment was set up in split plots, arranged in strips with four replicates. The absence or presence of HS using KS100 as the source was tested in the plots, and N fertilization (50; 75; 100; 125 and 150% of the recommended dose), using urea, was tested in the subplots. Soil pH, H+Al, Al3+, and Na+, K+, P, Ca2+, Mg2+, Fe2+, Mn2+ and Zn2+ contents were determined, and cation exchange capacity and bases saturation (V %) in the 0-0.2 and 0.2-0.4 m layers were calculated. Analyses of stocks of total organic carbon and carbon (C) of the humic acid, fulvic acid and humin fractions, and humic substances were performed. It was possible to observe that, in the second production cycle of West Indian cherry, the soils showed higher contents of nutrients available to plants. Increase in N availability did not enable a clear trend in the behavior of chemical attributes and organic C stocks in the soil. Under the studied conditions, KS100 application allowed a reduction in the C stocks of the HS of the soil.

Influence of Plant Growth Retardants and Nitrogen Doses on the Content of Plant Secondary Metabolites in Wheat, the Presence of Pests, and Soil Quality Parameters

Wheat is the cereal most susceptible to lodging, particularly during the flowering period and at the early ripening stage. The use of plant growth retardants (PGRs) is especially recommended when intensive nitrogen (N) fertilisation is applied, which increases the susceptibility of plants to lodging. This paper presents the results of tests into the effects of PGRs (PGR0—control; PGR1—chlormequat chloride (CCC) + trinexapac-ethyl (TE); PGR2—chlormequat chloride (CCC) + ethephon (ET)), and N dose—N0, N20, N40, and N60 [0, 20, 40, and 60 kg N ha−1] on the content of selected plant secondary metabolites (PSM) in the Indian dwarf wheat (Triticum sphaerococcum Percival) of the Trispa cultivar, and on the abundance of insect pests. In the developmental stage of wheat (BBCH 39), insects were collected with an entomological net. The study also investigated the effect of experimental factors on the physicobiochemical properties of the soil (pH in KC, granulometric composition, total organic carbon TOC, total nitrogen TN, fractional composition of humus, and the activity of enzymes). An increase in the plant secondary metabolite (PSM) and FRAP (ferring reducing ability of plasma) contents following the application of PGRs and N fertilisation already from as low a rate as 20 kg ha−1 was demonstrated. A significant positive correlation was noted between the abundance of Oulema spp. and the contents of total polyphenols, chlorogenic acid, and FRAP. No such relationship was noted for Aphididae or Thysanoptera. TOC content was higher on the plots on which N fertilisation was applied at the highest rate and after the application of PGRs. The factor determining the TN content was N fertilisation. Soil samples of the PGR0 N0 treatment were characterised by the greatest proportion of carbon in the humic and fulvic acid fractions and by the smallest proportion of carbon in the humin fraction. N fertilisation increased the proportion of carbon in the humin fraction on the plots on which no PGRs were applied. The study demonstrated an increase in the activity of oxidoreductive enzymes following the application of higher N rates. The application of PGRs resulted in no inhibition of enzymes in the soil compared to the control (PGRs0).

Sorption in soils and bioaccumulation potential of 2,2′-DiBBPA

2,2′-Dibromobisphenol A (2,2′-DiBBPA) is frequently detected in the environment. However, the mobility of 2,2′-DiBBPA in the soil environment is poorly understood. The present study examined the effects of soil components such as the NaClO-resistant fraction, dithionite-citrate-bicarbonate -demineralized fraction, humin fraction, black carbon, DOC-removed fraction, exogenous dissolved organic carbon and heavy metal cations on the adsorption of 2,2′-DiBBPA on several types of agricultural soils. The adsorption isotherms on soils and soil components were well fitted to the linear isotherm equation. 2,2′-DiBBPA sorption onto soils was dominated by soil organic matter content (SOM) and affected by exogenous dissolved organic carbon. Linear regression relationships between adsorption capacity (Kd) and soil characteristics were evaluated to predict partitioning of 2,2′-DiBBPA. Black carbon played a predominant role in the adsorption of 2,2′-DiBBPA. Heavy metal ions significantly inhibited the adsorptive behavior of 2,2′-DiBBPA under alkaline conditions. Semiempirical linear relationships were observed between biota-sediment accumulation factors (1.18–2.47)/logarithm of bioconcentration factors (BCFs, 2.49–2.52) of 2,2′-DiBBPA in lugworms and Kd. These results allow for the prediction of the bioaccumulation of 2,2′-DiBBPA in other soils. Furthermore, values of log BCF > 1.0 indicate the preferential bioaccumulation of 2,2′-DiBBPA in biota. These data are of significance for understanding the migration of 2,2′-DiBBPA in agricultural soils and bioaccumulation in organisms.

Effects of tillage practice on fungal and actinobacterial cellulolytic community with different humified particle‐size fractions in a double‐cropping paddy field

AbstractSoil cellulose plays a vital role in keeping or increasing carbon (C) cycling and fertility of rice fields. There is a close relation between soil fulvic acid (FA), humin (HM) fractions, and GH48, cbhI genes. However, the effects of different tillage practices on soil humus C content composition, GH48, and cbhI genes abundances in different soil particle‐size fractions of double‐cropping rice fields still need to be further investigated. Therefore, the impacts of different short‐term tillage practices on soil GH48 and cbhI genes abundances in double‐cropping rice fields were conducted. This experiment set up different tillage practices: rotary tillage with crop straw removed as a control (RTO), conventional tillage with crop straw in put (CT), rotary tillage with crop straw in put (RT), and no‐tillage with crop straw retain (NT). The result indicated that the distribution of soil humus, and GH48, cbhI genes abundances were significantly enhanced under combined applied with tillage and crop straw incorporation conditions. Soil FA, HM, and humic acid (HA) C content in 2000–50 μm and >2000 μm fractions with RTO treatment were significantly lower than that of CT, RT, and NT treatments. This result showed that oalkyl and alkyl of HA and FA in 2000–200, 200–50, 50–2, and 2–0.1 μm fractions with CT, RT, NT, and RTO treatments were lower than that of >2000 μm fraction. There was lower ARO% and more AL% of FA and HA in these fractions under the same tillage condition. The result showed that GH48 and cbhI genes abundances in these fractions with CT, RT, and NT treatments were significantly higher than that of RTO treatment. There had significantly positively correlated with GH48, cbhI genes abundances, and soil HA, FA, HM C contents, o‐alkyl C, and AL% of FA. Therefore, it was positively practiced for increasing GH48 and cbhI genes abundances in the double‐cropping rice fields by applying with tillage and crop straw incorporation.

Sequential extraction of labile and recalcitrant fractions of soil organic matter: A case study focusing on antimony (Sb) in humic acids, fulvic acids and humin fractions of long-term aged contaminated soils

Soil organic matter (SOM) plays a key role in environmental chemistry of macro and micro nutrients as well as heavy metal (loids). In this research, a modified sequential extraction scheme was used to isolate labile and recalcitrant SOM from organic rich soils after 18 months of ageing with antimony. Humic substances were extracted with a mixture of 0.5 M sodium hydroxide +0.1 M sodium pyrophosphate solution from soils. Then soils deprived of humic substances were sequentially subjected to extraction with glycerol, citric acid, pre-treated with acid and extracted with boiling alkali mixture. The humic acids (HA) and fulvic acids (FA) of isolated SOM fractions were separated and HAs been characterized using FTIR, 1H NMR, and UV-VIS. Acid-alkali treatment of the most recalcitrant SOM fraction (A1-ROM) led to the extraction of sparingly soluble, highly aromatic compound with considerable amounts of N (44% of the extractable N), possibly due to the breakdown of bounds between aromatic rings and amine functional groups. Nevertheless, the highest content of C and TOC was associated with the glycerol extractable SOM. Substantial amounts of Fe and Al were extracted with glycerol, resulting in a dramatic rise of Sb in SOM extracts. The largest increase (60%) in Sb concentrations was observed after the removal of Fe with citric acid. The humic substances (HS) were responsible for 63% of extractable Sb, whereas even after exhaustive alkali extractions 22% of the total Sb remained in the residual humin fraction. Within the HS fraction, 95% of antimony was associated with the low molecular weight FAs. Antimony concentrations in organic fractions correlated significantly with TOC and N contents, possibly due to the role of amine functional groups in Sb complexation. The results of this research highlight the importance of Fe–Al-SOM bridging and humin fraction in sequestration of Sb in recalcitrant SOM pools.

Compositional changes in the humin fraction resulting from the long-term cultivation of an Irish grassland soil: Evidence from FTIR and multi-NMR spectroscopies

Soil humin (HN), a major long-term sink for carbon in the pedosphere, plays a key role in the global carbon cycle, and has been less extensively studied than the humic and fulvic acids components. There are increasing concerns about the depletions of soil organic matter (SOM) arising from modern soil cultivation practices but there has been little focus on how HN can be altered as the result. This study has compared the HN components in a soil under cultivation for wheat for >30 years with those from an adjacent contiguous soil that had been under long-term grass for all that time. A urea-fortified basic solution isolated additional humic fractions from soils that had been exhaustively extracted in basic media. Then further exhaustive extractions of the residual soil material with dimethyl sulfoxide, amended with sulphuric acid isolated what may be called the “true” HN fraction. The long-term cultivation resulted in a loss of 53 % soil organic carbon in the surface soil. Infrared and multi-NMR spectroscopies showed the “true” HN to be dominated by aliphatic hydrocarbons and carboxylated structures, but with clear evidence for lesser amounts of carbohydrate and peptide materials, and with weaker evidence for lignin-derived substances. These lesser-amount structures can be sorbed on the soil mineral colloid surfaces and/or covered by the hydrophobic HN component or entrained within these which have strong affinities for the mineral colloids. HN from the cultivated site contained less carbohydrate and more carboxyl groups suggesting slow transformations took place resulting from the cultivation, but these were much slower than for the other components of SOM. It is recommended that a study be made of the HN in a soil under long-term cultivation for which the SOM content has reached a steady state and where HN will be expected to dominate the components of SOM.