Carbon Stabilization by Clays in the Environment

The role of biology in the formation, stabilization and degradation of soil structure

Interaction between humic acid and montmorillonite in the presence of calcium ions I. Interfacial and aqueous phase equilibria: Adsorption and complexation

Tillage is one of the oldest practices in agricultural production and offers many short term benefits in agro-ecosystem. These perceived benefits of tillage, however, have been gradually questioned because of its negative long-term consequences on soil and environment. Therefore conservation tillage systems have become the subject of intensive research among scientific communities and common practices among farming communities. However, scientific information on beneficial effects of conservation tillage systems on soil and environment is scattered. Critical analysis and synthesis of such information is helpful for scientific communities, farmers, students, and policy makers.This chapter reviews the impact of conservation tillage on soil organic matter, soil structure stability and soil organisms. Based on the analysis of available literature, it can be concluded that conservation tillage increases soil organic matter content. Most studies state that conservation tillage decreases the loss of carbon from the soil by reducing soil erosion loss and minimizing carbon loss by microbial respiration thus increasing soil organic matter. Some studies also found increased carbon input under conservation tillage system mainly through increased moisture and nutrient use efficiency of plants thereby increasing crop biomass production and its subsequent incorporation into the soil. Conservation tillage also enhances soil structural stability through its positive effects on soil moisture, organic matter and microbial activities. Accumulation of crop residues and organic matter in the surface layer under conservation tillage creates favourable feeding conditions and also provides physical protection to various soil organisms, thereby increasing their abundance as well as diversity. Various studies have shown that conservation tillage increases microbial biomass in soil from 80% to 200% as compared with conventional tillage system. Less soil disturbance, which is the characteristics of conservation tillage, has positive effects on soil properties, soil processes and soil organisms which interact in a complex way and together, they all enhance soil quality for agro-ecosystem productivity.

به‌منظور بررسی تأثیر کودهای آلی (اسید هیومیک و عصاره ورمی‌کمپوست) بر خصوصیات رشدی، مورفولوژیکی و فیتوشیمیایی مرزه خوزستانی (Satureja khuzistanica Jamzad.) آزمایشی در مزرعه تحقیقاتی شرکت دارویی خرمان در شهرستان خرم آباد در بهار 1392 به‌ صورت فاکتوریل در قالب بلوک‌های کامل تصادفی با سه تکرار انجام شد. تیمارهای مورد بررسی شامل سه غلظت 5، 10و 15 درصد عصاره ورمی‌کمپوست و مقادیر 5/1، 5/2 و 5/3 لیتر در هکتار اسید هیومیک بودند که به صورت محلول‌پاشی مورد استفاده قرار گرفتند. فاکتورهای مورد بررسی شامل، ارتفاع بوته، تاج بوته، طول و عرض برگ، عملکرد وزن خشک اندام هوایی، عملکرد وزن خشک برگ، بازده اسانس، عملکرد اسانس، محتوای فنل و فلاونوئید کل بودند. تیمارهای مختلف اسید هیومیک و عصاره ورمی‌کمپوست بر صفات مورفولوژیکی (ارتفاع بوته، تاج بوته، طول و عرض برگ) در طی چهار مرحله نمونه‌برداری قبل از گلدهی تأثیر معنی‌دار نداشتند. نتایج نشان داد که بیشترین مقدار وزن خشک اندام هوایی (460 گرم در متر‌مربع)، وزن خشک برگ (33/195 گرم در متر‌مربع) و عملکرد اسانس (38/6 گرم در متر‌مربع) در تیمار 5/3 لیتر در هکتار اسید هیومیک و غلظت 20 درصد عصاره ورمی‌کمپوست به‌دست آمد، که با تیمار شاهد اختلاف معنی‌داری را نشان داد. بیشترین درصد اسانس (43/3 درصد) در تیمار 5/1 لیتر در هکتار اسید هیومیک و غلظت 20 درصد عصاره ورمی‌کمپوست دیده شد. تیمار 5/2 لیتر در هکتار اسید هیومیک و غلظت 5 درصد عصاره ورمی‌کمپوست با (56/46 میکروگرم گالیک اسید در میلی‌گرم عصاره خشک) و تیمار 5/3 لیتر در هکتار اسید هیومیک و غلظت 5 درصد عصاره ورمی‌کمپوست با (13/749 میکروگرم روتین در میلی گرم عصاره خشک) به ترتیب بیشترین تأثیر را بر محتوای فنل و فلاونوئید داشتند. به نظر می‌رسد مصرف مقادیر مناسب از اسید ‌هیومیک و عصاره‌ ورمی‌کمپوست با افزایش مواد آلی خاک، از طریق بهبود فعالیت‌های میکروبی خاک و نیز فراهمی جذب بیشتر عناصر غذایی، سبب افزایش میزان فتوسنتز و ماده خشک گیاهی می‌گردد و در بین تیمار‌های بررسی شده، تیمار 5/3 لیتر در هکتار اسید هیومیک و غلظت 20 درصد عصاره ورمی‌کمپوست به عنوان یکی از بهترین تیمار شناخته شد.

Purpose The contamination of agricultural soils by heavy metals is a worldwide problem. Organic amendments can be used for the immobilization and binding of heavy metal ions in soils by complexation, adsorption, and precipitation. A field trial was carried out to evaluate the influence of some low-cost organic materials such as rice straw (RS), green manure (GM), and pig manure (PM) on the distribution of Cu and Cd and the retention of these metals by organic matter fractions in heavy metal-polluted soils. Materials and methods The experiment was conducted in Miaoyunao Village, Daye County, Hubei province, China. PM, GM (peanut plants), and RS were obtained from a farm close to the village. Sixteen treatments with three replicates were designed. Soil chemical properties such as soil pH, electrical conductivity (EC), organic matter (OM), and available P were measured by standard methods. Soluble/ exchangeable, organic-bound, inorganic precipitates and residual Cu and Cd in the soil were sequentially extracted and analyzed. The amounts of Cu and Cd bound with soil particulate organic matter (POM) fractions and humic substances were also determined. Results and discussion The addition of organic amendments declined significantly the concentrations of soluble/ exchangeable Cu and Cd, but increased the amounts of these metals in organic-bound and inorganic precipitate forms in the soil. RS was more effective than GM and PM in diminishing the solubility of Cu and Cd. The largest retention for Cu and Cd by humic substances and POM was noticedinRStreatments,whereasthelowestwasfoundinPM treatments. Humic substances showed higher potential in the fixation of Cu and Cd than POM fractions. The conversion of soluble/exchangeable Cu and Cd to other insoluble forms after the application of organic amendments may be ascribed to the increases of soil OM, pH, EC, and available P contents. The highest binding of Cu and Cd with POM fractions and humic substances after the incorporation of RS mainly resulted from the greatest increase of soil OM contents. Conclusions RS, GM, and PM can be employed as good and cheap substances for the immobilization of Cu and Cd in heavy metal-polluted soils. RS was the best amendment in decreasing the solubility of Cu and Cd, and also in enhancing the retention of these metals by humic substances and POM fractions in the soil. Futures studies should focus on the influence of these organic amendments or their mixtures on the phytotoxicity of Cu and Cd for different plants in heavy metal-contaminated soils.

Influence of HCl/HF treatment on organic matter in aquifer sediments: A Rock-Eval pyrolysis study

“Biogenic interference” is that portion of natural organic matter in soil that cannot be distinguished from petroleum in a standard test for contamination. Biogenic interference is normally a small fraction of total natural organic matter. In organic soils, however, biogenic interference alone can exceed “petroleum” limits set by regulatory agencies. A test using a pyrolysis-gas chromatograph/flame ionization detector (GC/FID) was developed to quantify biogenic interference in soil samples from northern Alaska. The samples had no known history of contamination, so all measured “petroleum” was derived from biogenic interference. The pyrolysis test was found to predict biogenic interference in soil samples more accurately than any combination of standard soil tests, including C:N ratio, pH, percent organic carbon, extractable carbon, humic acids, fulvic acids, low molecular weight acids, hydrophobic neutrals, and hydrophilic neutrals. Analysis of samples contaminated in the laboratory confirmed that the pyrolysis test could quantify biogenic interference in soils recently contaminated by petroleum.

The different origin of alginite and soil organic matter may be the reason of differences in their humic acids (HA) chemical structure. One of the aims of this article is to compare the chemical composition of alginite HA and HA isolated from different soil types. Another aim of this article is to compare the chemical structure of humic acids of alginite isolated with two different procedures: modified IHSS (International Humic Substances Society) method and simplified extraction method. The modified IHSS method was applied for the isolation of alginite and soil HA. To obtain sufficient amount of alginate HA for biological experiments, simplified extraction method suited for large volumes of HA was applied. The differences in elemental analysis and ash proportion in HA extracted by modified IHSS method (C = 35.4, H = 43 atomic%, ash content = 0.08%) and simplified extraction method (C = 31, H = 31 atomic%, ash content = 7.42%) can be caused by different concentration of extraction solution and also differences in purification of HA. The differences in chemical structure between alginate HA and HA isolated from different soil types according to the data of elemental analysis (C content of alginite HA = 35.4 atomic%, C content in soils HA = 38.2‒49.1 atomic%) and 13C nuclear magnetic resonance (NMR) spectra (degree of aromaticity of alginite HA = 24.4% and soil HA= 35.9‒53%) were found. Results of 13C NMR show that the content of aromatic carbon was decreasing in the following order: Haplic Chernozem HA > Andic Cambisol HA > Haplic Cambisol HA > alginite HA. Based on the obtained results, it can be concluded that the differences in the chemical structure of alginite and soil HA can be explained by the difference in the origin of organic matter in alginite and soil samples. The source of organic matter in alginite is mainly type II kerogen from algae and that of soil is lignin and cellulose (type III kerogen) of higher plants.

Compost-derived humic acid impacts on the biodechlorination of pentachlorophenol in high organic matter paddy soil

Reversed-phase high performance liquid chromatographic profile of organic fractions extracted by solvents with different polarity as a tool to evaluate the hydrophobic character of soil under different management

<p>Soil organic matter (SOM) is in the focus of research as it plays crucial role in soil fertility, carbon sequestration, and all adsorption related processes in the soil. Nevertheless, its compound and the methods to investigate it are rather diverse. Some approach prefers to define different theoretical carbon pools in the soil based on input and mineralization dynamics using mean residence times. Other studies apply physical and/or chemical fractionations of the soil to separate the various eg. mineral phase associated or aggregate occluded carbon pools to gain less heterogeneous material. However, in practice, these two approaches are hardly met each other. As a considerable part of SOM is strongly associated with the mineral colloid fraction or even cations its investigation reveals the question of extractions. Traditional methods aimed to extract pure SOM fractions such as fulvic and humic acids (FA; HA)  and characterized the whole SOM based on them, even though these pure fractions represented only a small part of the total SOM and were not present under natural conditions. Recent methods try to characterize the SOM using in situ samples where the role of organic mineral complexes is still not fully understood. As a result, findings based on several approaches are hardly comparable with each other. The present study aims to characterize SOM based on parallel in situ solid-phase investigation FA separation, and water dissolved organic matter extraction. The study site is a haplic Luvisol under plowing and conservation tillage. Fourier transform infrared spectroscopy on the solid phase fractions resulted in an inverse proportion between organic carbon content and aromaticity independently from tillage. The aggregate occluded SOM was characterized by the lack of aliphatic components, whereas the fine fraction, and the bulk soil associated SOM seemed to be rich in them. The water-soluble SOM revealed molecular size increase in both the fine fraction related and the aggregate occluded organic matter owing to plowing, nonetheless, aggregates occluded the same sized OM molecules as those attached to the fine fraction. In general, FA fractions provided more humified organic matter, whereas water dissolved SOM showed a more intensive microbiome origin. The photometric properties of the FA fractions did not differ between the tillage systems, except for the SUVA254, which provided higher aromaticity under conservation tillage due to the lack of plowing. Also, the water-soluble part of SOM showed more humified composition and increased aromaticity under conservation tillage compared to plowing tillage. As a consequence, beneath the fingerprint of recent microbial activity, DOM reflects soil organic matter composition as well, therefore it seems to be suitable as a direct SOM proxy. The present research was supported by the Hungarian National Research and Innovation Office (NKFIH) K-123953, which is kindly acknowledged.</p>

Biochar (B), as well as its combination with nitrogen (N) fertilization, can influence soil quality and fertility. Humus formation and aggregation is a long-term process in soils and the impact of combined biochar-N fertilization on its formation remains underexplored for long term studies. The aim of this study was to determine the extent to which combined biochar-N fertilization on the soil organic matter (SOM) content, quality of humic substances (HS), and soil structure. We also aimed at quantifying changes in the relationships between HS and soil structure. Silty loam Haplic Luvisol was sampled from the field after 1- and 9- years from the incorporation of biochar (0, 10, and 20 t ha− 1 of biochar marked as B0, B10, B20) combined with N fertilization (N0, N1, and N2). The results showed that B + N fertilization moderately increased the soil organic carbon (Corg) content in the soil after 1 year of incorporation. After 9 years, the Corg content in the soil was relatively balanced among the treatments. Only in B20N2 did the HS content significantly increase compared to B0N0. In B20N2, the content of microaggregates significantly decreased compared to B0N0 after 9 years. Significant changes in correlations between SOM, HS, and aggregate size fractions suggest potential shifts in their relationships over the decade. The gradual strengthening and changes in the intensity of positive or negative relationships between them suggests the aging of biochar may have long term effects on crop productivity and soil health.

Productivity of cropland soils, especially in semi-arid to arid zones, is declining due to increasing losses of stable organic matter. Therefore, it was found important to evaluate alternative management systems that can control, and if possible combat, these escalating losses of recalcitrant fractions of soil organic matter (SOM). The aim of this study was to quantify the influence of land use changes on humic substances of the semi-arid Plinthustalfs. Topsoil samples from distinctive agro-ecosystems at Harrismith, Tweespruit and Kroonstad were collected in the virgin, cultivated and restored Plinthustalfs and analysed for C and N in crude humic substances (Cs and Ns), extractable humic substances (Ce and Ne), humic acids (Ch and Nh) and fulvic acids (Cf and Nf). The results indicated that cultivation depleted the former virgin soils of crude humic substances, extractable humic substances, humic acids and fulvic acids across the three agro-ecosystems, with the exception of fulvic acids, which were higher in the cultivated soils than in the virgin soils of Kroonstad. Restored soils had substantial amounts of these humic fractions, except fulvic acids that behaved differently in the Kroonstad agro-ecosystem. Some correlations were observed between climate variables and humic fractions. In general, mean annual rainfall (MAR) and aridity index (AI) contributed to the loss of crude humic substances, extractable humic substances, humic acids and fulvic acids, while mean annual temperature (MAT) did not. These three climate variables did not influence the buildup of humic fractions. No trends were observed regarding the C/N ratios of the examined humic fractions; however, most were found to be closer to a range of 10–12, suggesting that SOM was approaching equilibrium state. Although it is known that humic substances are recalcitrant in nature, our results revealed that management practices that prohibit soil disturbance are needed to complement the refractory nature of humic substances against biological oxidation, and hence reduce C and N losses into the atmosphere.

Manure application can restore soil ecosystem services related to nutrient cycling and soil organic matter (SOM) dynamics through biochemical transformations mediated by soil enzymes. Soil enzymes are crucial in soil metabolic functioning, as they drive the decomposition of organic residues, humification processes, transformations leading to the release of plant available nutrients, stabilization of soil structure, and degradation of xenobiotic (foreign or strange) compounds. However, despite the fact that there is an exhaustive amount of literature available on the effects of manure on soil enzyme activities, there is no comprehensive overview of recent research findings that compares different management scenarios, manure types, and potentially new manure products or management. The purpose of this chapter is to provide a review of the response of enzyme activities to manure applications and their potential implications on soil biogeochemical cycling in agroecosystems. Additionally, this chapter intends to provide some perspective on specific areas where more information is warranted and pinpoint avenues for future research.

Speciation of rare earth elements in natural terrestrial waters: assessing the role of dissolved organic matter from the modeling approach