Soil Organic Components Research Articles

Soil Nitrogen Forms and Availability in Paddy Soil under Different Fertilization Methods

To reveal the characteristics of soil organic nitrogen components under different long-term fertilization methods in paddy fields, 7 typical paddy fields in the Yanbian Korean Autonomous Prefecture of Jilin Province were selected, and soil samples were collected from 0 to 10 cm and 10 to 20 cm. The samples were analyzed for available nitrogen, total nitrogen and inorganic nitrogen content and each component of organic nitrogen. The results showed that soil nitrogen decreased with increasing soil depth in the soil profile. Different fertilization methods had a significant or greater effect on the available nitrogen, total nitrogen and organic nitrogen in 0 to 10 cm soil, and it had a significant effect on the total nitrogen content in 10 to 20 cm soil. Combined applications of organic and inorganic fertilizer was beneficial for improving available soil nitrogen. Applying organic fertilizer was beneficial for the accumulation of total nitrogen and organic nitrogen. Organic nitrogen was a major part of soil nitrogen. In terms of directly affecting the path analysis, the effects of ammonia sugar nitrogen, acid-hydrolyzable unknown nitrogen and non-hydrolyzable nitrogen on available nitrogen are significant. A small negative correlation was shown between amino acid nitrogen and available nitrogen. Amino acid nitrogen indirectly affected the available nitrogen through other components. In terms of the general effect of the path analysis, the influence of non-hydrolyzable nitrogen to available nitrogen was the highest. An important factor to consider in relation to reasonable fertilization is that promoting non-hydrolyzable nitrogen and unknown acid-hydrolyzable nitrogen transformed into available nitrogen and accumulated available nitrogen.

Chemical Behavior of Lanthanum in the Presence of Soils Components: Adsorption and Humate Complexes

The inorganic and organic components of soils from a forest and from a semiarid region were separated and characterized by different techniques. The kinetic adsorption behavior of lanthanum ions by the inorganic components of the soils indicated that the systems behave according to the kinetic model of pseudo-second order, so 3 h of contact was sufficient to achieve equilibrium. The sorption isotherm data, qe vs. Ce, were best adjusted to the Langmuir model for the soil of the forest; this means that a monolayer is formed and that the energy of adsorption is the same in all adsorption sites so the material is homogeneous. The data for the soil of the semiarid area were adjusted to the Freundlich model; this indicates that the material is heterogeneous and multilayers are formed. The competition between the lanthanum sorption by the inorganic components and the formation of a complex with humic acids was shown by a decrease of qe. The method of Schubert was used to determine the stoichiometric coefficient of the complex La:(HA)n, which was 1:1 for both soils, whereas the \( \log {\beta}_{La,{(HA)}_n}^{app} \) was 5.1 ± 0.2 for the soil of the forest and 7 ± 1 for the semiarid soil.

Micromorphological analysis on the influence of the soil mineral composition on short-term aggregation in semi-arid Mediterranean soils .

Aggregation in soils is the result of the interaction of the soil organic components and soil minerals. The reactivity of the mineral phase is acknowledged to interfere with aggregates formation and stabilization, but its influence on aggregation in semi-arid Mediterranean soils remains mostly unknown. In this study, we used micromorphological analysis of aggregates formed in a 28-d incubation in two agricultural soils differing only in the composition of the mineral phase in the upper Ap horizon (a carbonate-depleted Palexeralf with 21.5% clay, and a contiguous carbonate-rich Typic Calcixerept with 20.9% clay before decarbonation which was reduced to 10.4% upon decarbonation). The two soils belong to the same agricultural field and have had similar management for decades. Soil samples were completely disaggregated into their fractions < 250 μm, and incubated with fresh organic matter to stimulate re-aggregation. Macroaggregates (> 2 mm) formed during the incubation were separated at days 3, 7, 14, 21 and 28 and used to prepare thin sections. Macroaggregates were more abundant at day 3, and then decreased in number in the two soils, which indicates a dependency between organic matter decomposition and stable macroaggregates formation. They contained a greater proportion of smaller aggregates in the decarbonated soil. Micromorphological analysis revealed significant differences in the fabric and physical characteristics of these macroaggregates, in which bonds among primary particles were observed to be led by clays in the Palexeralf while the coarse fraction appeared embedded in a micromass with crystallitic b-fabric corresponding to carbonates in the Calcixerept. This resulted in a more compact fabric and less porosity in macroaggregates in the Calcixerept. Image analysis of thin sections was used to quantify and characterize the pore system of macroaggregates. Porosity (pores > 20 μm) was more than double (36.9% for 15.6%) within macroaggregates in the decarbonated soil, with more elongated pores. Although in both soils most pores were 20 to 150-μm in equivalent diameter, some porosity > 150 μm was observed only in macroaggregates from the decarbonated soil. These observations allow hypothesizing that the mechanisms responsible for aggregates stabilization and/or formation are different in the two soils, and that they result in different physical characteristics of soil aggregates. The implications of such differences on air and water flow rates within aggregates, and thus on the soil microbial activity and organic matter decomposition, as well as on soil erodibility, need to be studied and accounted for when evaluating the effect of soil management and other practices on soil quality in semi-arid Mediterranean agrosystems.

Effects of Different Fertilization Methods on Organic Nitrogen Components in Paddy Soil

In order to reveal characteristics of soil organic nitrogen components under long-term different fertilization methods on paddy field, selected 7 typical paddy field of Korean Autonomous Prefecture of Yanbian of Jilin Province, collected soil samples of 0 to 10 cm and 10 to 20 cm, analyzed total nitrogen content of soil and each component of organic nitrogen. Results showed that effects of different fertilization methods on content of soil total acid hydrolysable N (TAHN), amino acid N (AAN), ammonia sugar N (ASN), acid-hydrolysable unknown N (AUN) in 0 to 10 cm soil had significant influence or more, and non hydrolysable N (NHN), AAN and ASN accounted for proportion of total N (TN) had significant influence. Effects soil organic nitrogen components in 10 to 20 cm soil had not significant influence. Applying organic fertilizer was beneficial to improve soil total organic nitrogen, mainly by improving content of AAN and ASN; Long-term application inorganic fertilizer led to NHN accumulation, but applying organic fertilizer was beneficial to NHN transformation, increase content of AAN; TAHN, NHN, AN, AAN, ASN content in 0 to 10 cm soil were slightly higher than that in 10 to 20 cm soil, and content of HUN had no obvious regularity between two soil layers.

Prion protein interaction with soil humic substances: environmental implications.

Transmissible spongiform encephalopathies (TSE) are fatal neurodegenerative disorders caused by prions. Animal TSE include scrapie in sheep and goats, and chronic wasting disease (CWD) in cervids. Effective management of scrapie in many parts of the world, and of CWD in North American deer population is complicated by the persistence of prions in the environment. After shedding from diseased animals, prions persist in soil, withstanding biotic and abiotic degradation. As soil is a complex, multi-component system of both mineral and organic components, it is important to understand which soil compounds may interact with prions and thus contribute to disease transmission. Several studies have investigated the role of different soil minerals in prion adsorption and infectivity; we focused our attention on the interaction of soil organic components, the humic substances (HS), with recombinant prion protein (recPrP) material. We evaluated the kinetics of recPrP adsorption, providing a structural and biochemical characterization of chemical adducts using different experimental approaches. Here we show that HS act as potent anti-prion agents in prion infected neuronal cells and in the amyloid seeding assays: HS adsorb both recPrP and prions, thus sequestering them from the prion replication process. We interpreted our findings as highly relevant from an environmental point of view, as the adsorption of prions in HS may affect their availability and consequently hinder the environmental transmission of prion diseases in ruminants.

Mineral-associated organic carbon and black carbon in restored wetlands

Stable soil organic carbon (SSOC) has a vital influence on soil's capacity for resisting disturbance and sequestering carbon. However, studies of the SSOC in restored wetlands are incomplete. We studied mineral-associated organic carbon (MOC) and black carbon (BC), two representatives of SSOC, in a wetland restoration chronosequence in Caizi Lake, East China. MOC was analyzed by both a physical method, involving dividing soil into size-fractions POM (>53 μm) and MOM (0.45–53 μm) and detecting OC in MOM (MOCP), and a chemical method, acidifying soil with hydrofluoric acid (HF) and detecting OC loss (MOCC). BC was analyzed by methods using dichromate (BCCr) and chemothermal oxidation (BCCTO). MOCC, BCCr, and BCCTO were further determined in MOM for comparing results from different fractions and methods. We found an elevation of soil ecological function in wetlands restored from farmlands in Caizi Lake, which was supported by a general increase of MOC and BC with time after restoration at surface soil (0–6 cm). Comparison of methods showed that size fractionation method overestimated MOC by identifying all OC in MOM as MOC, since HF-soluble OC accounted for no more than 23.5% of the whole OC in MOM. As it may separate more components, e.g. charcoal, from BC continuum, the dichromate method was recommended as more meaningful in the study of BC recovery in restored wetlands with biomass-burning history. We presented the possible use of ratio (BCCr–BCCTO):BCCTO for BC source identification which produced a reasonable result similar to that of a commonly used method. The combination of physical and chemical fractionation methods revealed that the proportion of BC to TOC in POM was considerable, which indicated that POM was not invariably labile as was commonly understood. Finally, a detailed list of soil organic carbon components including MOC, BC and labile OC in each size fraction was represented by using sequential analysis and combination of fractionation methods.

The content and toxicity of heavy metals in soils affected by aerial emissions from the Pechenganikel plant

The zoning of the terrestrial ecosystems exposed to the aerial emissions from the Pechenganikel plant (Murmansk oblast) was performed; it was based on the state of the soil cover in 2012. The following parameters were determined: the pH, the contents of heavy metals (HMs) and exchangeable calcium and magnesium, the proportion between the organic and mineral soil components, and the state of the soil micro-biota. Three zones differing in the intensity of the soil pollution were distinguished: the zone of strong pollution (at a distance of 3 km from the source of the emission), the zone of medium pollution (16 km), and the zone of weak pollution (25–30 km to the southwest from the pollution source). In the last ten years, the soil pollution in the zone influenced by aerial emissions from the Pechenganikel plant has remained the same. The amount of bacteria and fungi in the air is directly related to that in the soil. The results obtained point to the bacterial pollution of the atmosphere nearby the industrial center. In the vicinity of the plant, gram-negative bacteria (Gracilicutes) predominate in the air; in remote areas, gram-positive bacteria (Fermicutes) are dominants. In the air nearby the industrial center, potentially pathogenic fungi (Gongronella butleri and Alternaria alternata) were revealed.

A comparison of the compositional differences between humic fractions isolated by the IHSS and exhaustive extraction procedures

Humic substances (HSs), consisting, on the basis of solubilities in aqueous acid and basic media, of humic acids (HAs), fulvic acids (FAs), and humin (Hu), are the major components of soil organic matter (SOM). Most studies of soil/natural organic matter (SOM/NOM) have been carried out on extracts of soils in dilute sodium hydroxide solutions, the solvent used to extract the Standards of the International Humic Substances Society (IHSS). However, Hu, the major component in the classical definition of HSs, is insoluble in aqueous base and is not isolated by the traditional IHSS method. Recently, a sequential exhaustive extraction (SEE) process has been shown to be capable of isolating and separating the major components of the classically defined HSs from the soils of the temperate and tropical regions. The SEE system was used in the present study to isolate the HA/FA and Hu fractions from a subtropical volcanic Taiwanese soil. Chemical and compositional properties of these extracts were then compared with similarly obtained isolates from soils from the different climatic regions. Increases in the aliphatic relative to aromatic carbon contents were observed for both the HA and FA fractions when the pH values of the extraction media were increased. HAs and FAs isolated using the SEE method have spectroscopic profiles similar to those from the IHSS isolate; however, the cumulative extraction efficiency (%) of the SEE method (65 %) for the volcanic soil was much higher than for the traditional IHSS method (33 %). When the residual volcanic soil, following extractions once, three, and eight times with 0.1 M NaOH were then extracted with dimethyl sulphoxide (DMSO) plus concentrated sulphuric acid (the final solvent in the SEE sequence) it was seen that the content of crystalline polymethylene hydrocarbon (33 ppm (13)C-NMR resonance in the Hu (or DMSO/acid)) extract increased relative to the amorphous methylene (30 ppm). That highlights the difficulty in dissolving the more highly ordered hydrocarbon structures that would be expected to have closer associations with the mineral colloids. Although the SEE procedure isolated all of the HAs and FAs from the Yangmingshan soil, extractability of the Hu from the volcanic soil in the DMSO/acid solvent was low (21 %), and contrasted with the much higher yields from temperate and tropical regions. The decreased Hu extraction may arise from its associations with the extensive iron and aluminium hydroxide mineral colloids in the soil. The Hu from this sub-tropical soil was different from the Hus isolated from other soil types, indicating the need to isolate and characterise these recalcitrant organic material in order to understand the organic carbon components in soils in greater detail. Such results would indicate that more attention should be given to mineral colloids in soils, and to the organo/mineral associations that will have an important role in the stabilities of OM in the soil environment.

Properties and structure of raised bog peat humic acids

Humic substances form most of the organic components of soil, peat and natural waters, and their structure and properties differ very much depending on their source. The aims of this study are to characterize humic acids (HAs) from raised bog peat, to evaluate the homogeneity of peat HAs within peat profiles, and to study peat humification impact on properties of HAs. A major impact on the structure of peat HAs have lignin-free raised bog biota (dominantly represented by bryophytes of different origin). On diagenesis scale, peat HAs have an intermediate position between the living organic matter and coal organic matter, and their structure is formed in a process in which more labile structures (carbohydrates, amino acids, etc.) are destroyed, while thermodynamically more stable aromatic and polyaromatic structures emerge as a result of abiotic synthesis. However, in comparison with soil, aquatic and other HAs, aromaticity of peat HAs is much lower. Comparatively, the raised bog peat HAs are at the beginning of the transformation process of living organic matter. Concentrations of carboxyl and phenolic hydroxyl groups change depending on the peat age and decomposition degree from where HAs have been isolated, and carboxylic acidity of peat HAs increases with peat depth and humification degree.

Organic nitrogen components in soils from southeast China.

To investigate the amounts of extractable organic nitrogen (EON), and the relationships between EON and total extractable nitrogen (TEN), especially the amino acids (AAs) adsorbed by soils, and a series of other hydrolyzed soil nitrogen indices in typical land use soil types from southeast China. Under traditional agricultural planting conditions, the functions of EON, especially AAs in the rhizosphere and in bulk soil zones were also investigated. Pot experiments were conducted using plants of pakchoi (Brassica chinensis L.) and rice (Oryza sativa L.). In the rhizosphere and bulk soil zone studies, organic nitrogen components were extracted with either distilled water, 0.5 mol/L K2SO4 or acid hydrolysis. K2SO4-EON constituted more than 30% of TEN pools. K2SO4-extractable AAs accounted for 25% of EON pools and nearly 10% of TEN pools in rhizosphere soils. Overall, both K2SO4-EON and extractable AAs contents had positive correlations with TEN pools. EON represented a major component of TEN pools in garden and paddy soils under traditional planting conditions. Although only a small proportion of the EON was present in the form of water-extractable and K2SO4-extractable AAs, the release of AAs from soil exchangeable sites might be an important source of organic nitrogen (N) for plant growth. Our findings suggest that the content of most organic forms of N was significantly greater in rhizosphere than in bulk soil zone samples. However, it was also apparent that the TEN pool content was lower in rhizosphere than in bulk soil samples without added N.

Adsorption of tetrabromobisphenol A on soils: Contribution of soil components and influence of soil properties

The adsorption of tetrabromobisphenol A (TBBPA) on several typical Chinese soils and soil mineral and organic components were comprehensively investigated in the present study. The adsorption isotherms were well described by the Freundlich equation and the corresponding adsorption capacity constant Kf ranged from 2.46 to 357.30L/kg and 16.52 to 136,731.98L/kg for the original soils and the soil components, respectively. Correlation analysis between the adsorption capacity and soil properties indicates that soil pH and soil organic carbon (SOC) content were the predominant factors determining TBBPA adsorption on the soils. At constant pH of 7.0, the soils with higher SOC content exhibited stronger adsorption affinity for TBBPA, suggesting the significant importance of SOC in the adsorption. The adsorption affinity of TBBPA became weaken for a given soil with increasing pH due to the enhanced electrostatic repulsion between the anionic TBBPA species and soil surface. Humins and black carbon of SOC played a predominant role in while soil minerals contributed slightly to the adsorption of TBBPA on the soils. The results of this study will provide a better understanding of the behaviors of TBBPA in soils.

Lead and zinc in the structure of organic and mineral soil components

In addition to the more reactive forms, metals can occur in the structure of minerals, and the sum of all these forms defines their total contents in different soil fractions. The isomorphic substitution of heavy metals for example alters the dimensions of the unit cell and mineral size. This study proposed a method of chemical fractionation of heavy metals, using more powerful extraction methods, to remove the organic and different mineral phases completely. Soil samples were taken from eight soil profiles (0-10, 10-20 and 20-40 cm) in a Pb mining and metallurgy area in Adrianópolis, Paraná, Brazil. The Pb and Zn concentrations were determined in the following fractions (complete phase removal in each sequential extraction): exchangeable; carbonates; organic matter; amorphous and crystalline Fe oxides; Al oxide, amorphous aluminosilicates and kaolinite; and residual fractions. The complete removal of organic matter and mineral phases in sequential extractions resulted in low participation of residual forms of Pb and Zn in the total concentrations of these metals in the soils: there was lower association of metals with primary and 2:1 minerals and refractory oxides. The powerful methods used here allow an identification of the complete metal-mineral associations, such as the occurrence of Pb and Zn in the structure of the minerals. The higher incidence of Zn than Pb in the structure of Fe oxides, due to isomorphic substitution, was attributed to a smaller difference between the ionic radius of Zn2+ and Fe3+.

Change of PAHs with evolution of paddy soils from prehistoric to present over the last six millennia in the Yangtze River Delta region, China

To evaluate the influence of hydroponics management on soil organic components with evolution of paddy soil over the last six millennia, PAHs, as a biomarker, as well as total organic carbon content were used to explore changes of paddy soil organic carbon in two entirely buried ancient paddy soil profiles. The results showed that hydroponics management can cause organic carbon deposition in rice paddy. The changing of total PAH concentrations was not always in accordance with the changing of total organic carbon contents in layers of the buried ancient paddy soils. The PAHs in 6280BP prehistoric paddy soil layer was 3-ring>5-ring>4-ring>6-ring, while in layers of the present paddy soil and the prehistoric upland were 3-ring>4-ring>5-ring>6-ring. The contribution of phenanthrene to total PAHs in two profiles and the increasing ratio of phenanthrene to alkylated PAHs from parent material/6280BP prehistoric upland to 6280BP paddy suggested substantial increase of the anthropogenic influence of hydroponics management on rice paddy soil. And in view of the 14C age and bioremains in the two profiles, it was only possible for PAHs to be derived from hydroponics management with evolution of the paddy soils form the Neolithic age. Cadalene could be used as an indicator for biological sources of PAHs released by rice plant residues, and benzo[g,h,i]fluoranthene and benzo[g,h,i]perylene for pyrogenic sources released by field vegetation fires.

In-Situ Molecular-Level Elucidation of Organofluorine Binding Sites in a Whole Peat Soil

The chemical nature of xenobiotic binding sites in soils is of vital importance to environmental biogeochemistry. Interactions between xenobiotics and the naturally occurring organic constituents of soils are strongly correlated to environmental persistence, bioaccessibility, and ecotoxicity. Nevertheless, because of the complex structural and chemical heterogeneity of soils, studies of these interactions are most commonly performed indirectly, using correlative methods, fractionation, or chemical modification. Here we identify the organic components of an unmodified peat soil where some organofluorine xenobiotic compounds interact using direct molecular-level methods. Using (19)F→(1)H cross-polarization magic angle spinning (CP-MAS) nuclear magnetic resonance (NMR) spectroscopy, the (19)F nuclei of organofluorine compounds are used to induce observable transverse magnetization in the (1)H nuclei of organic components of the soil with which they interact after sorption. The observed (19)F→(1)H CP-MAS spectra and dynamics are compared to those produced using model soil organic compounds, lignin and albumin. It is found that lignin-like components can account for the interactions observed in this soil for heptafluoronaphthol (HFNap) while protein structures can account for the interactions observed for perfluorooctanoic acid (PFOA). This study employs novel comprehensive multi-phase (CMP) NMR technology that permits the application of solution-, gel-, and solid-state NMR experiments on intact soil samples in their swollen state.

Application of 210Pbex inventories to measure net hillslope erosion at burned sites

ABSTRACTFallout radionuclides, including lead‐210 excess (210Pbex), have been broadly and successfully used to quantify net hillslope sediment transport in agricultural, pastoral and forested landscapes but have only recently been applied in burned terrain. Quantifying post‐fire erosion is important because fires can amplify hillslope erosion, impacting terrestrial and aquatic habitat and water quality. However, we lack a basic understanding of the fate of 210Pbex in fires. To address this knowledge gap, we collected over 400 soil samples from unburned, moderately and severely burned forested sites in central Idaho. We measured soil 210Pbex content at stable reference and eroding sites and in mineral and organic soil components. At all sites, organic matter had the highest concentration of 210Pbex, representing 30% to 73% of the total activity. At the severely and moderately burned sites, 210Pbex reference inventories were lower by 58% and 41%, with about 40% less organic mass, relative to the unburned site. These results indicate that most 210Pbex in our semi‐arid, forested sites was bound to organic matter, and that a substantial portion of this lead was lost due to forest fires. These losses likely occurred through volatilization and wind transport of smoke and ash. In the moderately burned site, 210Pbex losses were more spatially variable, potentially due to spatially uneven fire intensity and effects. Despite equal percent losses of 210Pbex, lower inventories at the burned sites produced lower calculated net erosion rates relative to the unburned site. Thus, given methodological uncertainties, 210Pbex losses due to fire, and the subsequent sensitivity of calculated net erosion rates to these lower 210Pbex inventories, we suggest this method should not be used in burned terrain to calculate absolute net erosion and deposition rates. However, within a given burned site, 210Pbex inventories still provide useful information describing relative soil losses and storage across the landscape. Copyright © 2012 John Wiley & Sons, Ltd.

Application of FTIR spectroscopy for evaluation of hydrophobic/hydrophilic organic components in arable soil

The main aim of this study was to determine the intensity of hydrophobic/hydrophilic components of the soil’s organic matter as well as its hydrophobicity. Non-destructive Fourier Transform Infrared (FTIR) spectroscopy was used for the diagnosis and characterization of the basic classes of the chemical groups (hydrophilic and hydrophobic components) from which the organic matter in the soils is formed. Soil samples (depth 0–30 cm) were taken from the topsoil of the 70 sampling sites from the experimental field at Prague-Ruzyne (Czech Republic) during 2007–2009, where a conventional soil tillage technology was used. It was found that the variability of the intensity of the hydrophobic components is greater (27.6%) than that of the intensity of the hydrophilic components (6.2%), which correlated significantly with the C<sub>org</sub> (r = 0.58; P < 0.05) and N<sub>t</sub> (r = 0.65; P < 0.05) in the soil. It was proven that the soil samples with a higher proportion of coarse grains are more hydrophobic than those with higher proportions of clay. Data about soil hydrophobicity can help to evaluate the soil quality parameters as well as the soil fertility.  

Intra- versus inter-site macroscale variation in biogeochemical properties along a paddy soil chronosequence

Abstract. In order to assess the intrinsic heterogeneity of paddy soils, a set of biogeochemical soil parameters was investigated in five field replicates of seven paddy fields (50, 100, 300, 500, 700, 1000, and 2000 yr of wetland rice cultivation), one flooded paddy nursery, one tidal wetland (TW), and one freshwater site (FW) from a coastal area at Hangzhou Bay, Zhejiang Province, China. All soils evolved from a marine tidal flat substrate due to land reclamation. The biogeochemical parameters based on their properties were differentiated into (i) a group behaving conservatively (TC, TOC, TN, TS, magnetic susceptibility, soil lightness and colour parameters, δ13C, δ15N, lipids and n-alkanes) and (ii) one encompassing more labile properties or fast cycling components (Nmic, Cmic, nitrate, ammonium, DON and DOC). The macroscale heterogeneity in paddy soils was assessed by evaluating intra- versus inter-site spatial variability of biogeochemical properties using statistical data analysis (descriptive, explorative and non-parametric). Results show that the intrinsic heterogeneity of paddy soil organic and minerogenic components per field is smaller than between study sites. The coefficient of variation (CV) values of conservative parameters varied in a low range (10% to 20%), decreasing from younger towards older paddy soils. This indicates a declining variability of soil biogeochemical properties in longer used cropping sites according to progress in soil evolution. A generally higher variation of CV values (>20–40%) observed for labile parameters implies a need for substantially higher sampling frequency when investigating these as compared to more conservative parameters. Since the representativeness of the sampling strategy could be sufficiently demonstrated, an investigation of long-term carbon accumulation/sequestration trends in topsoils of the 2000 yr paddy chronosequence under wetland rice cultivation restricted was conducted. Observations cannot be extrapolated to global scale but with coastal paddy fields developed on marine tidal flat substrates after land reclamation in the Zhejiang Province represent a small fraction (<1%) of the total rice cropping area. The evolutionary trend showed that the biogeochemical signatures characteristic for paddy soils were fully developed in less than 300 yr since onset of wetland rice cultivation. A six-fold increase of topsoil TOC suggests a substantial gain in CO2 sequestration potential when marine tidal wetland substrate developed to 2000 yr old paddy soil.

Airborne hyperspectral imaging of spatial soil organic carbon heterogeneity at the field-scale

A detailed knowledge on the heterogeneity of the soil organic carbon (SOC) content in agricultural soils is required to support applications such as precision agriculture and soil C monitoring. Imaging spectroscopy in the visible (VIS) and near-infrared (NIR) region has proven to be highly sensitive to organic soil components and can efficiently provide data with high spatial resolution. The objectives of our study were (i) to test the suitability of airborne hyperspectral imaging for the characterisation of the spatial heterogeneity of the SOC content at the field-scale, (ii) to investigate the impact of various soil surface conditions (roughness, vegetation) on SOC prediction and (iii) to produce SOC maps for arable fields on a pixel-wise basis. The soil reflectance was recorded by the aircraft-mounted hyperspectral sensor HyMap (450–2500nm) on test sites with the following varying soil surface conditions: bare soil, fine seed-bed; ploughed, bare soil; volunteer crops; straw residues. A partial least squares regression (PLSR) was performed for data analysis. Our results reveal an accurate prediction of the SOC content at a comparatively small concentration range (8.3 to 18.5gSOCkg−1) on long-term uniformly cultivated fields. Site-specific characteristics influenced the calibration models; highest prediction accuracy was performed over a bare, fine soil (RMSEP=0.76gSOCkg−1; RPD=2.08). A generated pixel-wise map (8m×8m) allows the detection of small-scale spatial variability of SOC content and comparatively more realistic than an interpolated map. Thus, airborne hyperspectral imaging constitutes a substantial progress compared to point observations and facilitates well-directed applications in precision agriculture.

Isotopically distinct modern carbonates in abandoned livestock corrals in northern Kenya

We report δ18O and δ13C data from modern carbonate in soils and dung samples from 3 recently abandoned livestock corrals in northern Kenya. Calcium carbonate content is higher within ∼5 cm depth that contains a mixture of dung and surface soils of corrals than in soils below 5 cm depth. We radiocarbon dated carbonates from 0.5 to 40 cm depths in two corrals and one control site. Surface carbonates (0.5 cm) from the two corrals were formed from modern carbon (>1955) when the corrals were active, while all other carbon is >16,000 years (BP) old. Shallow carbonate is also enriched in 18O (δ18O up to 3.0‰) and depleted in 13C (δ13C up to −12.0‰) with respect to carbonate at deeper levels and at two control sites. The δ18O and δ13C of soil carbonates (δ18OSC and δ13CSC respectively) in corrals are inversely correlated for depths up to about 15 cm where organic carbon is greater than 0.5%. Below that depth, there is a positive correlation between δ18OSC and δ13CSC values, similar to that observed in a control site.In concordance with the increase in δ18OSC and the decrease in δ13CSC values in corral surface soils, the δ15N of soil organic matter (SOM) (δ15NSOM) decreases with depth in corral soils, but in a control site shows a slight increase within the first 5 cm and then becomes relatively constant with depth. Dung-laden organic matter at corral surfaces is enriched in 15N by ∼5‰ relative to surface SOM of control sites. The δ15NSOM values imply that dung enriches the surface soils of livestock corrals in15N.The observed δ15NSOM and δ18OSC trends suggest microbially-mediated carbonate precipitation in the dung, a conclusion that is supported by δ13CSC and δ18OSC trends and the radiocarbon data. The calcium carbonate from the dung is released in the soil as dung mixes with the mineral phases of the soil.Changes in land use have resulted in more sedentary lifestyles among many pastoral communities, so corrals are likely to become increasingly important in conferring long-lasting transformations of the organic and inorganic components of soils that may lead to shifts in soil properties. The δ13CSC and δ18OSC therefore add to the toolbox for identifying former animal encampments in archaeological sites occupied by pastoral communities.

Effect of water regimes on sorptivity and organic matter humic components of soil

Effect of water regimes on sorptivity and organic matter humic components of soilThe aim of the study was to find the effect of water regimes on soil sorptivity and humic components of organic matter. Physicochemical parameters were also determined. Steady state cumulative infiltration was the highest (60-100 mm) in non-irrigated upland soil and the lowest (8-10 mm) in waterlogged soil. The highest sorptivity of 4.0-4.5 mm min-1/2was found in non-irrigated upland soil and the lowest in seasonally waterlogged soil (1.0-1.5 mm min-1/2). Organic carbon content of all soils was low (<1%), EC values were also low (< 4 dS m-1). Saturated moisture was high in waterlogged soil. The non-irrigated upland soils had a higher fraction of fulvic acid (0.15-0.2%), due to which they were more capable of infiltration, whereas waterlogged soils had a greater fraction of insoluble humic acid (0.29-0.35%) and exhibited less cumulative infiltration. Sorptivity decreased as the clay content, pH, EC, porosity and humic acid content of the soil increased.