scholarly journals Mineral-associated soil organic matter: characteristics and behavior under diagenesis

2021 ◽  
Vol 4 (4) ◽  
Author(s):  
T. V. Alekseeva
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Isotopic Composition ◽  
Structural Characteristics ◽  
Chemical Properties ◽  
13C Nmr Spectroscopy ◽  
Adsorption Selectivity ◽  
H2o2 Treatment ◽  
Soil Humus ◽  
Carboxylic Groups

The main part of soil organic matter (OM) is mineral-associated: 88 ± 11% of С and even more – 93 ± 9% of N. The aims of the given study were: 1 – to demonstrate experimentally the adsorption selectivity of organic compounds towards minerals with different physico-chemical properties (palygorskite vs montmorillonite); 2 – to characterize mineral-associated OM of buried Late Holocene palaeosols and estimate its diagenetic transformations; 3 – to investigate the OM of humin from modern soils of different genesis and Pleistocene and Holocene palaeosols and estimate its diagenetic transformations. The basic soil properties were determined using standard methods. Clay fractions (<2 um) – natural organo-mineral complexes (OMC) were obtained by sedimentation, their mineralogy was studied by XRD. The elemental composition of OM was studied with CNS-analyzer. The structural characteristics of organic matter were determined with the solid-state 13C-NMR-spectroscopy and FTIR-spectroscopy, isotopic composition of C and N – by mass-spectrometry. The obtained results show that the characteristics of mineral-associated OM depends on the properties of mineral “filter” as well as the fate of OM under diagenesis: how long, in what quantity and quality it will persist. It was shown that palygorskite adsorbed predominantly O-alkyls, which are chemically strongly bound. As a result, the age of fulvic type humus in palygoskite palaeosols can reach 300 My. From other side humus of smectitic paleosols of the same age is present by deeply transformed aromatic structures (“coal”). Mineral-associated OM of buried under kurgans Holocene palaeosols contains more alkyls and carboxylic groups, is less aromatic in a comparison with OM of the respective soils. The specific feature of mineral-associated OM is its enrichment in N-compounds. The later are present by both vegetal and microbial compounds, and demonstrate the large affinity towards the mineral surfaces. The formation of chemical bounds between them provides the persistence of OM in OMC. E.g. H2O2 treatment results in preferential destruction of C-rich compounds and oxidized OM demonstrates larger C/N values. Mineral-associated OM of buried Holocene soils keeps the decreased values of C/N (7–14 vs 14–21 for OM of whole soils). Additionally they are characterized by heavier isotopic composition of δ15N in a comparison with the respective soils (5–11‰ vs 6–9‰). It could be explained either by the accumulation of microbial N, or increasing of the humification degree – the loss of aliphatic C and increasing of aromaticity. Humin is the considerable part of soil humus. Experimentally shown that OM of humins both of soils and OMC is enriched in O-alkyls and C of acetal groups. OM of humins are not homogeneous, and consists from at least two groups: mineral-associated OM and partly mineralized plant fragments. As a consequence, the content of humin in OMC is smaller in a comparison with respective soils. It is concluded that mineral-associated OM and humin as well as soil humus represent dynamic soil systems.

Structural and dynamic properties of soil organic-matter as reflected by 13C natural-abundance, pyrolysis mass-spectrometry and solid-state 13C NMR-spectroscopy in density fractions of an oxisol under forest and pasture

Soil Research ◽  
1995 ◽  
Vol 33 (1) ◽  
pp. 59 ◽  
Author(s):  
A Golchin ◽  
JM Oades ◽  
JO Skjemstad ◽  
P Clarke
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Isotopic Composition ◽  
Particulate Organic Matter ◽  
Organic Materials ◽  
Natural Abundance ◽  
13C Natural Abundance ◽  
Clay Particles ◽  
Density Fractions ◽  
Soil Organic Matter Turnover

Changes in the content and isotopic composition of organic carbon as a consequence of deforestation and pasture establishment were studied in three neighbouring areas on an Oxisol from Australia and used to measure the turnover of forest-derived carbon (C3) under pasture (C4) over 35 and 83 year time scales. The results indicated that the quantity of forest-derived carbon declined rapidly during the first 35 years under pasture but the content remained nearly stable thereafter, suggesting the presence of two pools of carbon with different turnover times. The calculated values for turnover time of labile and resistant fractions of forest-derived carbon were 35 and 144 years respectively. The soil samples were separated into five fractions with densities <1.6 (free and occluded), 1.6-1.8, 1.8-2.0 and >2.0 Mg m-3. Based on the spatial distribution of organic materials within the mineral matrix of soil, the soil organic matter contained in different density fractions was classified as free particulate organic matter (1.6 free), occluded particulate organic matter (<1.6 occluded, 1.6-1.8 and 1.8-2.0) and clay associated organic matter (>2.0 Mg m-3). The 13C natural abundance showed that the free particulate organic matter formed a significant pool for soil organic matter turnover when the forest was replaced by pasture. Compared with free particulate organic matter, the organic materials occluded within aggregates had slower turnover times. The occluded organic materials were in different stages of decomposition and had different chemical stabilities. Comparison of the chemistry and isotopic composition of occluded organic materials indicated that the O-alkyl C content of the occluded organic materials was inversely related to their stabilities whereas their aromatic C content was directly related to their stabilities. In soils under pasture, a considerable amount of forest-derived carbon was associated with clay particles in the fractions .2.0 Mg m-3. The rate of accumulation of pasture-derived carbon was also rapid in this fraction, indicating the presence of two different pools of carbon (C3 and C4) associated with clay particles. The forest-derived carbon had the highest stability in the fractions >2.0 Mg m-3, probably due to strong interaction with active aluminium or iron and aluminium oxides associated with clay surfaces.

scholarly journals Soil fertility, organic carbon and fractions of the organic matter at different distances from eucalyptus stumps

2009 ◽  
Vol 33 (3) ◽  
pp. 571-579 ◽  
Author(s):  
Geraldo Erli Faria ◽  
Nairam Félix de Barros ◽  
Roberto Ferreira Novais ◽  
Ivo Ribeiro Silva
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Organic Carbon ◽  
Soil Layer ◽  
Chemical Properties ◽  
Soil Surface ◽  
Light Fraction ◽  
Forest Residues ◽  
Chemical Attributes ◽  
Topsoil Layer

Knowledge on variations in vertical, horizontal and temporal characteristics of the soil chemical properties under eucalyptus stumps left in the soil is of fundamental importance for the management of subsequent crops. The objective of this work was to evaluate the effect of eucalyptus stumps (ES) left after cutting on the spatial variability of chemical characteristics in a dystrophic Yellow Argisol in the eastern coastal plain region of Brazil. For this purpose, ES left for 31 and 54 months were selected in two experimental areas with similar characteristics, to assess the decomposition effects of the stumps on soil chemical attributes. Soil samples were collected directly around these ES, and at distances of 30, 60, 90, 120 and 150 cm away from them, in the layers 0-10, 10-20 and 20-40 cm along the row of ES, which is in-between the rows of eucalyptus trees of a new plantation, grown at a spacing of 3 x 3 m. The soil was sampled in five replications in plots of 900 m² each and the samples analyzed for pH, available P and K (Mehlich-1), exchangeable Al, Ca and Mg, total organic carbon (TOC) and C content in humic substances (HS) and in the free light fraction. The pH values and P, K, Ca2+, Mg2+ and Al3+ contents varied between the soil layers with increasing distance from the 31 and 54-monthold stumps. The highest pH, P, K, Ca2+ and Mg2+ values and the lowest Al3+ content were found in the surface soil layer. The TOC of the various fractions of soil organic matter decreased with increasing distance from the 31 and 54-month-old ES in the 0-10 and 10-20 cm layers, indicating that the root (and stump) cycling and rhizodeposition contribute to maintain soil organic matter. The C contents of the free light fraction, of the HS and TOC fractions were higher in the topsoil layer under the ES left for 31 months due to the higher clay levels of this layer, than in those found under the 54-month-old stumps. However, highest C levels of the different fractions of soil organic matter in the topsoil layer reflect the deposition and maintenance of forest residues on the soil surface, mainly after forest harvest.

scholarly journals Mechanisms of improving coastal saline-alkali soil by periphyton

2021 ◽  
Author(s):  
Ye Zhu ◽  
Tianyun Shao ◽  
Yujie Zhou ◽  
Xiumei Gao ◽  
Xiaohua Long ◽  
...  
Keyword(s):  
Organic Matter ◽  
Enzyme Activity ◽  
Soil Organic Matter ◽  
Relative Abundance ◽  
Ph Value ◽  
Chemical Properties ◽  
Functional Genes ◽  
Control Soil ◽  
Alkali Soil ◽  
Unplanted Soil

Periphyton plays an indispensable role in coastal saline-alkali land, but its function is poorly understood. Soil physical and chemical properties (pH value, salinity, soil organic matter), enzyme activity and microbial diversity (based on 16s rDNA, ITS and functional genes) were measured in periphyton formed on rice-growing coastal saline-alkali soil modified by a new type of soil conditioner. The results showed that the content of organic matter and catalase activity in periphyton were significantly higher than in the unplanted control soil. Soil pH and salinity were decreased in periphyton compared to the unplanted control soil. Based on the relative abundance, bacterial genera Desulfomicrobium, Rhodobacter, cyanobacterium_scsio_T−2, Gemmatimonas, and Salinarimonas as well as fungal genus Fusarium were more abundant in periphyton than the unplanted control soil. In terms of functional genes, the cbbM and cbbL sequencing showed higher abundance of Hydrogenophaga, Rhodovulum, Magnetospira, Leptothrix, and Thiohalorhabdus, whereas the nifH sequencing indicated higher abundance of Cyanobacteria in the periphyton compared to the unplanted soil. The relative abundance and community structure of soil microorganisms were improved by periphyton, thus reducing soil salinity and pH, increasing soil organic matter and enzyme activity. This indicated that the periphyton can improve the conditions and offer a suitable environment for plant growth in coastal saline-alkali soil.

scholarly journals Hydrogen dynamics in soil organic matter as determined by <sup>13</sup>C and <sup>2</sup>H labeling experiments

2016 ◽  
Author(s):  
Alexia Paul ◽  
Christine Hatté ◽  
Lucie Pastor ◽  
Yves Thiry ◽  
Françoise Siclet ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Isotopic Composition ◽  
Bulk Material ◽  
Isotopic Signature ◽  
Close Link ◽  
Carbon Cycles ◽  
Exchangeable Hydrogen ◽  
Terrestrial Environments ◽  
Water Hydrogen

Abstract. Understanding hydrogen dynamics in soil organic matter is important to predict the fate of 3H in terrestrial environments. One way to resolve hydrogen fate and to point out processes is to examine the isotopic signature of the element in soil. However, non-exchangeable hydrogen isotopic signal in soil is complex and depends on the fate of organic compounds and microbial biosyntheses that incorporate water-derived hydrogen. To decipher this complex system and to understand the close link between hydrogen and carbon cycles, we followed labeled hydrogen and labeled carbon all along natural-like soil incubations. We performed incubation experiments with three labeling conditions: 1- 13C2H double-labeled molecules in the presence of 1H2O, 2- 13C-labeled molecules in the presence of 2H2O, 3- no molecule addition in the presence of 2H2O. The preservation of substrate-derived hydrogen after one year of incubation (ca. 5 % in most cases) was lower than the preservation of substrate-derived carbon (30 % in average). We highlighted that 70 % of the C-H bonds are broken during the degradation of the molecule which permits the exchange with water hydrogen. Added molecules are used more for trophic resources. The isotopic composition of the non-exchangeable hydrogen was mainly driven by the incorporation of water hydrogen during microbial biosynthesis. It is linearly correlated with the amount of carbon that is degraded in the soil. The quantitative incorporation of water hydrogen in bulk material and lipids demonstrates that non-exchangeable hydrogen exists in both organic and mineral-bound forms. The proportion of the latter depends on soil type and minerals. This experiment quantified the processes affecting the isotopic composition of non-exchangeable hydrogen, and the results can be used to predict the fate of tritium in the ecosystem or the water deuterium signature in organic matter.

Effect of Tillage and Cover Crop on Fluometuron Adsorption and Degradation under Controlled Conditions

Weed Science ◽  
1994 ◽  
Vol 42 (4) ◽  
pp. 629-634 ◽  
Author(s):  
Blake A. Brown ◽  
Robert M. Hayes ◽  
Donald D. Tyler ◽  
Thomas C. Mueller
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Soil Ph ◽  
Cover Crop ◽  
Soil Depth ◽  
Organic Matter Content ◽  
Chemical Properties ◽  
Exchange Capacity ◽  
Matter Content ◽  
No Till

Fluometuron adsorption and degradation were determined in soil collected at three depths from no-till + no cover, conventional-till + no cover, no-till + vetch cover, and conventional-till + vetch cover in continuous cotton. These combinations of tillage + cover crop + soil depth imparted a range of organic matter and pH to the soil. Soil organic matter and pH ranged from 0.9 to 2.5% and from 4.7 to 6.5, respectively. Fluometuron adsorption was affected by soil depth, tillage, and cover crop. In surface soils (0 to 4 cm), fluometuron adsorption was greater in no-till + vetch plots than in conventional-tilled + no cover plots. Soil adsorption of fluometuron was positively correlated with organic matter content and cation exchange capacity. Fluometuron degradation was not affected by adsorption, and degradation empirically fit a first-order model. Soil organic matter content had no apparent effect on fluometuron degradation rate. Fluometuron degradation was more rapid at soil pH > 6 than at pH ≤ 5, indicating a potential shift in microbial activity or population due to lower soil pH. Fluometuron half-life ranged from 49 to 90 d. These data indicate that tillage and cover crop may affect soil dissipation of fluometuron by altering soil physical and chemical properties that affect fluometuron degrading microorganisms or bioavailability.

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