Allophane Content Research Articles

Perspective of soil carbon sequestration in Chilean volcanic soils

We analysed a large dataset consisting of 457 soil profiles of Andisols and Ultisols of volcanic origin compared to 60 non-volcanic soils. We hypothesised that soil pH has a greater impact on the development of Al-organomineral complexes in volcanic soils compared to non-volcanic soils, in the latter, the silt and clay fractions play a crucial role. Soil pH >4.5 strongly influenced the formation of Al-organomineral complexes in volcanic soils, while an increase in allophane content led to a decrease in SOC. Ultisols with more crystalline clays, such as halloysite and disordered kaolinite, the pH had a weaker impact and there was no effect on non-volcanic soils. Instead, a positive correlation (R2 = 0.63, p < 0.01) was found between silt and clay and SOC in non-volcanic soils, supporting our second hypothesis. Soil pH played a significant role in the interplay between Al-organomineral complexes and allophane formation, while crystalline mineralogy has a direct effect on SOC levels in non-volcanic soils.

Effects of microtopography on within-field spatial variation of inherent soil properties in Andosols of Tokachi district, Hokkaido

ABSTRACT In large-scale upland cropping systems, understanding the magnitude of soil property variations and mapping the distribution are essential to improve soil nutrient management. The Tokachi district of Hokkaido has large-scale upland fields, and the soils are dominated by Andosols that inherently have characteristic clay minerals and high soil organic carbon content. In the region, microtopography is known to exist that can affect soil formation and within-field variation of the inherent soil properties. However, limited information exists about the relationship between microtopography and the spatial variation of inherent soil properties that are important for nutrient dynamics. Therefore, this study aimed to assess the effect of microtopography on the within-field variation of inherent soil properties in Andosols of Tokachi district, Hokkaido. Within a 6.6-ha field with an elevation difference of 3.2 m, four soil profiles were surveyed at different topographical positions, and 530 surface soil samples were collected at 12-m intervals. Samples were analyzed for total carbon (TC), acid-oxalate extractable Al, Fe, and Si (Alo, Feo, and Sio), pyrophosphate extractable Al and Fe (Alp and Fep), cation exchange capacity (CEC), and phosphate absorption coefficient (PAC). Geostatistical analysis was applied to understand the spatial structure of the surface soil properties. All soil profiles were dominated by volcanic parent materials, and they were classified into different types of Andosols. An exceptional variation of inherent soil properties was found in the surface soil, with TC content ranging from 35.2 to 124 g kg−1 and CEC from 20.3 to 55.7 cmolc kg−1. Geostatistical analysis showed that TC content varied over a large distance (range: 226 m) while allophane content varied at a shorter distance (range: 118 m). Our findings revealed that microtopography affected the soil water dynamics and erosion of the surface soil particles which caused the variation of TC, CEC, and allophane. Further studies must be conducted to understand the effects of the variation of these inherent soil properties on soil nutrient availability and crop productivity.

Selective separation and immobilization process of 137Cs from high-level liquid waste based on silicon-based heteropoly salt and natural minerals

• Silicon-based composite adsorbent was effective for 137 Cs removal. • The interaction mechanism of Cs was studied at the molecular level by density functional theory. • A conceptual process for separation and long-term safe disposal of Cs was proposed. A macro porous silica-based ammonium phosphomolybdate (AMP/SiO 2 ) adsorbent was synthesized and tested for separation and recovery of 137 Cs from real radioactive liquid waste. The excellent adsorption ability and high selectivity of AMP/SiO 2 for 137 Cs were confirmed. AMP/SiO 2 had relatively large decontamination efficiency of 137 Cs exceeding 99% in radioactive wastes, and the decontamination factors of 137 Cs were estimated to be 688 and 270 after adsorption in radioactive waste at 1 and 3 mol/L HNO 3 , respectively. In column operation, the separation and recovery of Cs(I) and coexisting ions could be realized using different eluents, and the recovery rate of Cs(I) was more than 90%. The Cs 3d and Mo 3d X-ray photoelectron spectroscopic spectra of AMP/SiO 2 before and after Cs(I) adsorption, suggesting that the ion exchange process of cesium with crystal lattice cations was the governing mechanism, and cesium ions could spontaneously react with approximately two ammonium ions in each AMP lattice by density functional theory simulation. Further, the crystal binding energy of each revised model showed an upward trend with the progress of the adsorption. After sintering at 1200 °C, CsAlSiO 4 , which could stably solidify eluted cesium, was formed in the allophane-based solidified product. The crystalline properties and volume reduction effect of the sintered products were enhanced with the increase in the allophane content. Ba(II) hardly entered the lattice of CsAlSiO 4 and occupied the Cs(I) site, resulting in minor changes in the crystal structure with substitution of Ba(II) for Cs(I).

Allophanes, a significant soil pool of silicon for plants

While in tropical soils recycling of plant phytoliths has been shown to represent a major pool of Si available for plants, the main Si pools available for plants in temperate soils are still poorly constrained. We characterised the various Si pools of temperate forested and cultivated soils in France by selecting seven paired sites (adjacent wheat and forest plots) for four soil groups: Luvisols, Albeluvisols, calcaric and hypereutric Cambisols. We showed that CaCl2-extracted Si (bioavailable) is mostly controlled by pH and allophanes (short-range ordered aluminosilicates) but not by phytoliths. Cultivation, by decreasing the soil organic carbon content increases the allophane content and the SiCaCl2 concentration. Our work highlights the importance of allophanes as the missing link between the soil solution and the clay minerals that could explain the reported correlation between the clay mineral content and bioavailable Si.

Rainfall is the major driver of plant Si availability in perudic gibbsitic Andosols

The amount of water available to leach solutes from soil is one of the major features determining mineral weathering, mineral neoformation and soil properties. It affects the fate of dissolved silicon (Si), which may follow four routes: leaching, mineral synthesis, adsorption, uptake by plants forming phytoliths. Here, we quantify the reservoirs of bioavailable Si and phytolithic Si in topsoils (0–20 cm) from wet tropical Andosols along a climosequence where mean annual rainfall (MAR) increases from 2650 to 4400 mm with increasing altitude (65–375 m asl) in Basse-Terre, Guadeloupe. We assessed bioavailable Si through CaCl2 extraction in soil, and foliar analysis in banana plants. We evaluated the pool of phytolithic Si through Na2CO3 extraction and heavy liquid separation. The Na2CO3 extraction was performed on both the bulk soil and oxalate–treated soil (ox-Na2CO3) cleared of its amorphous aluminosilicates. The Andosols have reached an advanced weathering stage. Their secondary products included (Al, Fe)–humus complexes, ferrihydrite, gibbsite, poorly crystalline Al hydroxide, and aluminous allophanic substances. The contents of organic C, metal-humus, ferrihydrite and gibbsite increased in soils in the wettest conditions (>3000 mm) whereas allophane content concomitantly decreased. Silicon leaf content varied little (3.8–5.3 g kg−1), but slightly decreased with increasing MAR (r = −0.48). Bioavailable Si content in soil decreased from 63 to 12 mg kg−1 with increasing MAR (r = −0.92), and was strongly correlated (r = +0.95) to that of phytolithic Si as assessed after ox-Na2CO3 extraction, linked to fresh, labile phytoliths. The Si/Al atomic ratio of the ox-Na2CO3 extract regularly decreased from 1.06 to 0.37 with increasing MAR, hence corroborating strongest desilication in soils in the wettest conditions. In these highly leached, gibbsitic Andosols, rainfall is thus the major driver of plant Si availability.

Carbon Mineralization Controls in Top- and Subsoil Horizons of Two Andisols Under Temperate Old-Growth Rain Forest

The effect of mineral properties on soil organic carbon (SOC) destabilization processes is poorly known. Andisols developed under temperate old-growth rain forest store important amounts of SOC due to strong mineral adsorption capacity. We evaluated the effect of mineral soil properties on microbial activity and native SOC mineralization in an incubation experiment with and without the addition of labile organic carbon (C) and nutrients. Top- and subsoil horizons of two Andisols with contrasting age from temperate old-growth rain forest were sampled. We used the selective dissolution methods to determine the metals complexed with SOC and allophane content. Radiocarbon analysis activity was performed to determine the 14C activity and 14C ages of all soils as a proxy for SOC persistence. Additionally, we carried out a laboratory incubation under controlled conditions with and without 13C labeled cellulose and nutrient solution (NH4NO3, KH2PO4) addition. A lower microbial activity in the subsoils of both Andisols compared to topsoils in accordance with the lower 14C activity at depth was recorded. After cellulose and nutrient additions, both subsoils horizons showed native SOC mineralization after 80 days of incubation. In contrast, these amendments did not induce native SOC mineralization in topsoils showing differences on C turnover rates between top- and subsoil horizons. In both soils, the native SOC mineralization after labile C and nutrient additions was negatively related to Na-pyrophosphate extractable C and may therefore be controlled by the formation of organo-mineral complexes with increasing soil C age. We conclude that the physicochemical soil characteristics evolving during pedogenesis control the SOC stabilization and also destabilization processes in Andisols developed under temperate old-growth rain forests.

Relationship between allophane with labile carbon and nitrogen fractions of soil in organic and conventional vegetable farming systems

Allophane is a characteristic of Andisols whose presence can absorb soil organic matter. One of soil organic matter fractions called the “labile fraction” is currently an appropriate indicator in determining soil quality. However, there is limited information concerning the relationship between allophane and the labile fraction. This study assessed the content of allophane by selective dissolution methods and calculated the labile fraction of particulate organic matter and microbial activity related to the carbon (C) and nitrogen (N) soil cycles in organic and conventional vegetable farming systems of two depths (0–25 cm and 25–50 cm). The content of the labile fractions of C and N in organic farming systems is higher than in conventional farming systems, which is also higher in the upper layer compared to the lower layer. However, the availability of allophane in the upper layer and organic system tends to be low. Therefore, allophane has a strong negative correlation with the labile fractions of carbon and nitrogen. The results of this study estimate that phosphorus (P) sorption is higher in soils containing quite high allophane. Hence, an organic farming system that has low allophane content will result in higher P availability for plants.

Unexpectedly higher soil organic carbon accumulation in the evapotranspiration cover of a coal bottom ash mixed landfill

Monolayer barriers, which are usually known as evapotranspiration (ET) covers, have long been used as alternative final cover systems in waste landfills. Coal bottom ash was evaluated as a good alternative to soil in landfill ET cover systems to increase the bottom ash (BA) recycling ratio in the past. In a previous study, applying BA promoted plant growth characteristics and improved the soil physicochemical properties, particularly the soil organic carbon (SOC) content. In this study, we investigated the effect of BA on the SOC increase by examining the chemical and physical characteristics of ET cover systems, and we compared BA mixed and pure soils. We collected two types of soil from the landfill cover, namely, BA mixed soil (BA 35% + soil 65%) and soil alone (100%), for treatments during the 5th year after installation. Bottom ash mixed soil has four times more SOC than the pure soil at the surface soil layer, but the SOC contents significantly decreased with the soil depth in BA mixed soil, and no differences were found between BA mixed soil and pure soil below a 25 cm soil depth. In addition, there was no significant difference in the chemical composition of the SOC according to a13C NMR. However, the allophane contents were significantly higher in BA mixed soil than pure soil, which physically protects the material from organic matter decomposition. Conclusively, the higher allophane content originating from BA might act as the primary factor in the high accumulation of soil organic carbon in the BA mixed soil layer by retarding the organic matter decomposition.

Distribution of Available Silicon of Volcanic Ash Soils in Jeju Island

In soils, dissolved silicon (Si) is adsorbed onto soil particles or is leached into groundwater through the soil profile. Andisols may play an important role in contributing to high dissolved Si concentrations in groundwater on Jeju Island, Korea. In this study, we evaluated the available Si content that potentially affects groundwater composition and investigated the relationship between the available Si content and chemical properties of volcanic ash soil on Jeju Island. We used the 1 M sodium acetate buffer (pH 4.0) to extract the available Si. Selected chemical properties were determined for 290 topsoil samples collected from different land sites throughout Jeju Island, and we analyzed the available Si content in the typifying pedons of Jeju Island and mainland Korea. The available Si content in Jeju Island topsoils ranged from 75 to 150 mg·kg−1, and the available Si content of Andisols in both orchards and grasslands was significantly higher than that of non-Andisols. The available Si content was highly correlated with the amounts of oxalate extractable Si, Al, and Fe in Andisols and was negatively related to the Alp/Alo ratio. With increasing elevation, we detected a decrease in the available Si and allophane content in Andisols, whereas Al-humus complexes increased with increasing elevation. The ratio of available Si in the lowest subsoil/topsoil increased to a value of 6.0, indicating that large amounts of available Si are present in the subsoil. The available Si content in the lowest subsoil of Andisols on Jeju Island was 10 times higher than that in the typifying pedons of the Korean mainland. In contrast, there were no differences in the available Si content between the topsoil and the subsoil of the typifying pedon series of Jeju and mainland non-Andisols because of differences in pedogenic processes. Collectively, our findings indicate that weathering of Andisols on Jeju Island potentially affects the Si concentration in groundwater.

Impacts of land use on hydrodynamic properties and pore architecture of volcanic soils from the Mexican Highlands

Volcanic soils are important resources because of their unique mineralogical and physical characteristics, and allophanic Andosols represent some of the world’s most fertile soils. However, their unique properties can be lost when cultivated. Most soils in the Central Valley, Mexico, are derived from volcanic materials. This valley encompasses one of the largest water supply systems in the world by volume, but is affected by soil degradation and deforestation. Sustainably managing volcanic soils requires understanding how land use affects their hydrodynamic properties. Gas adsorption and mercury intrusion porosimetry, water retention curves, tension infiltrometry and X-ray tomography were used to describe pore structure characteristics. Two volcanic soils (one Andosol and one derived from indurated tuff – Tepetates), three land uses (maize monoculture, maize–wheat rotation and fallow) and two horizons (Ap and A2 for maize monoculture and maize–wheat rotation) were studied. Tillage affected topsoil by increasing the sand fraction by 38% and decreasing total porosity and macroporosity by 23% and 40% respectively. Macropore size was reduced and the number of isolated macropores was higher in the tilled layer under maize, compared with untilled subsoil. The plot under maize–wheat rotation had lower allophane content, and saturated hydraulic conductivity was reduced by nearly an order of magnitude and water retention by half, compared with maize and fallow plots. Compared with Andosols, Tepetates showed differences in mineralogical composition with lower contents of amorphous compounds and in its porous network characteristics with twice the total and percolating macroporosity compared with the maize plot. Its high content of organic carbon (3.5%) seemed beneficial for its hydrodynamic properties. Sustainable agricultural management of these volcanic soils requires reducing mechanised tillage, avoiding periods when soil is bare, not applying maize–wheat rotation and applying maize–fallow rotation allowing natural vegetation growth.

Development of a method to extract protozoan DNA from black soil

ObjectivesMicroorganisms in environmental samples are identified by sequential screening, isolation, and culture steps, followed by the verification of physiological characteristics and morphological classification. Isolation and purification of Amoebae from soil samples is extremely complex, laborious, and time-consuming and require considerable expertise for morphological evaluation. PCR testing of soil DNA seems to be an effective means for protozoa habitat screening. In this study, we added Acanthamoeba sp. (MK strain) to soil and developed a method of extracting protozoan DNA from the soil. MethodsSoil allophane is a known DNA adsorbing substance that inhibits the PCR reaction. After comparing the soil properties and allophane contents of 7 soil samples, we attempted to combine multiple cell disruption and DNA purification methods to design an optimal soil DNA extraction method that can be used for downstream PCR analysis. ResultsWe compared five different crushing/refining methods. Amplification of the gene was confirmed by Acanthamoeba specific PCR in protocol V where the concentration of Acanthamoeba in soil (1.0 × 102/g) was the detection limit of PCR. ConclusionThe soil DNA extraction method following protocol V allows DNA amplification of protozoa, including Amoeba, which is difficult to cultivate, thus simplifying the investigation of protozoa habitats and genetic analyses.

Charge fingerprint in relation to mineralogical composition of Quaternary volcanic ash along a climatic gradient on Java Island, Indonesia

We studied the relationship between the mineralogical composition and surface charge properties of representative Quaternary volcanic ash soils, classified as Andosols, along an East-West sequence on Java Island in Indonesia. The soil charge characteristics were determined using ‘charge fingerprinting’ procedures. Most of the studied soils have a limited ability to retain cations under their forest or grass vegetation. The surface charge properties of these soils are mainly related to allophane and organic matter contents and, to a lesser degree, to ferrihydrite content and layer silicate characteristics. In East Java, the soils are Andosols with low allophane content, dominated either by halloysitic clays or by a mixture of 2:1 and 1:1 layer silicate clays; these soils are characterized by a low to moderate permanent charge. In West Java, the soils are rich in allophane, with subordinate kaolinitic clays, gibbsitic material or a mixture of 1:1 and 2:1 layer silicate clays; in contrast to the allophane-poor soils of East Java, these soils have extreme variable charge characteristics, creating a net ‘positive’ variable surface charge at soil pH. Differences in mineralogical composition of the clay fraction are attributed mainly to more pronounced seasonality in East Java, with variations in parent ash composition, becoming more acidic from east to west, as subordinate factor. The more severely leaching environment in West Java results in a higher degree of desilication, which led to a higher point of zero net charge (PZNC) and pHo in the allophane-rich soils. This study demonstrates how a climatic gradient can affect regional variations in charge properties, through the impact of climate on the mineralogical composition of the clay fraction. Regional patterns of this type must be understood to correctly assess of variations in soil fertility status and to make correct soil management choices for sustainable crop production.

Changes in soil carbon inputs and outputs along a tropical altitudinal gradient of volcanic soils under intensive agriculture

Volcanic soils contain a large stock of soil organic carbon (SOC) which is highly vulnerable to changes in land use and climate warming. In this study we examine the changes of SOC stocks along a tropical elevation gradient (100 m–700 m; +437 mm yr−1 of rainfall and −0.7 °C every 100 m), which is subject to two intensive agricultural systems (banana monoculture and vegetable crops) characterised by the heavy use of fertilisers and pesticides. We hypothesise that in these systems SOC is mainly controlled by soil mineralogy, climatic factors and soil tillage. We used a process-based approach to determine soil C inputs and outputs along the elevation gradient. The banana monoculture systems (198 plots) are characterised by a temporal steady-state of SOC, and the vegetable crop systems (55 plots) present high annual SOC losses. The banana systems were used to determine for the first time the altitudinal change in the in situ rate constant of SOC mineralisation (kSOC). Under banana monoculture, SOC stock increased by 218%, C input from crop residues decreased by 44%, and kSOC decreased by 570% across the altitudinal gradient. These results indicated that the SOC gradient was mainly induced by changes in C outputs. Allophane content increased with altitude (R2 = 0.61; 8 g kg−1 every 100 m) and was positively correlated with SOC content (R2 = 0.51) and negatively correlated with kSOC (R2 = 0.53). We hypothesise that the physical protection of SOC within amorphous allophanic minerals was the main factor responsible for the kSOC and SOC stock gradients. Strictly, the effects of allophane content and rainfall cannot be separated because soil mineralogy in the studied area is mainly determined by the level of rainfall. Our process-based analysis indicated that changes in temperature along the elevation gradient could only explain 22% of the observed change in kSOC. SOC stocks under vegetable crops also increased with altitude; they were 57% lower than under banana at low altitude but only 9% lower at high altitude. This reflected simultaneously the higher C outputs under vegetable crops due to more intensive soil tillage, and the greater resilience to soil disturbance of protected SOC in altitude. The results suggested that neither soil nutrient content nor soil biological properties contributed to the SOC and kSOC gradients under the intensive cropping systems analysed during this study. Overall, we conclude that SOC might be more vulnerable to soil tillage and warming in low-altitude soils.

Keterkaitan parameter nilai pH, C-organik, N-Total, C/N dan alofan pada beberapa Andisols di Jawa Barat

The correlation of chemical parameters and soil mineralogy one to another in Andisols were interesting to be studied, to increase the understanding of soil reactions, nutrient availability and soil mineral content. Andisols from three locations and derived from three different volcanic eruptions namely G. Tangkuban Parahu, G. Patuha and G. Tilu, with andesite, andesite-basalt and basalt parent materials respectively, were examined the correlation of several soil parameters. The values of pH, organic carbon, total nitrogen, C/N and allophane content were obtained from the soil analysis of every horizon of the soil profiles at each site. Correlation analyses were used to see the relationship of the parameters. The results showed a negative correlation between pH and organic carbon (r = -590 *). The soil pH values were positively correlated with the amount of allophane (r = 0.687 *). The pH values were correlated positively with imogolite content (r = 0.356 *). The pH values were negatively correlated with organic carbon (r = -0.590 *). The organic carbon content was negatively correlated with depth (r = - 0.582 *). The organic carbon content was negatively correlated with allophane (r = 0.707 *). Total nitrogen values were negatively correlated with increasing depth (r = -0.531 *).Keywords: Mt. Tangkuban Parahu, Mt. Patuha, Mt. Tilu, andesit, andesit-basalan, alophane

The pesticide chlordecone is trapped in the tortuous mesoporosity of allophane clays.

Some volcanic soils like andosols contain short-range order nanoclays (allophane) which build aggregates with a tortuous and fractal microstructure. The aim of the work was to study the influence of the microstructure and mesoporosity of the allophane aggregates on the pesticide chlordecone retention in soils. Our study shows that the allophane microstructure favors pollutants accumulation and sequestration in soils. We put forth the importance of the mesoporous microstructure of the allophane aggregates for pollutant trapping in andosols. We show that the soil contamination increases with the allophane content but also with the mesopore volume, the tortuosity, and the size of the fractal aggregate. Moreover, the pore structure of the allophane aggregates at nanoscale favors the pesticide retention. The fractal and tortuous aggregates of nanoparticles play the role of nanolabyrinths. It is suggested that chlordecone storage in allophanic soils could be the result of the low transport properties (permeability and diffusion) in the allophane aggregates. The poor accessibility to the pesticide trapped in the mesopore of allophane aggregates could explain the lower pollutant release in the environment.

Photoelectrochemical properties of dye-dispersing allophane–titania composite electrodes

Dye-dispersing allophane–titania composite electrodes were prepared from titanium alkoxide sols containing dye and allophane. The photoelectric conversion properties of the electrodes were investigated by photoelectrochemical measurements. The photocurrent values in the UV range decreased with an increase in the allophane content, whereas those in the visible range were increased by adding 1.0% (Al/Ti ratio) allophane. As a small amount of allophane nanoparticles were highly dispersed in the titania electrodes, the dye molecules were dispersed in the electrodes without decreasing the efficiency of the electron injection from the dye to the titania conduction band. The dye molecules dispersed on the titania nanoparticle surface were capped with allophane nanoparticles which prevented desorption. The dye molecules strongly interacted with the titania nanoparticle surface and efficiently injected the excited electrons into the titania conduction band.

Role of allophanes in the accumulation of glomalin‐related soil protein in tropical soils (Martinique, French West Indies)

SummaryThermo‐stable, operationally defined soil protein, known as glomalin, may make an important contribution to carbon storage in soils. The term glomalin is used because this putative protein, or group of proteins, was originally thought to be produced only by Glomus fungi. There is currently little information on the glomalin‐related soil protein (GRSP) content of tropical soils, particularly allophanic soils that are known to have different carbon dynamics to temperate climate soils. We have measured the Bradford‐reactive GRSP content of soils sampled from forests and grasslands on the tropical island of Martinique and compared the observations with soil composition. Two operationally defined fractions of GRSP were measured, namely easily‐extractable and total GRSP. The contents of GRSP in moist soils were in the range of 2–36 g kg−1, accounting for about 8% of soil organic carbon, and were greater in topsoils than in corresponding subsoils. Both the GRSP contents and the fraction of soil organic carbon attributed to GRSP were greater than those reported for temperate climate soils. Both total and easily extractable GRSP contents were positively correlated to soil organic carbon content. The fraction of soil organic carbon that could be attributed to soil protein decreased with increasing allophane content for allophanic soils. No other trends of GRSP content with soil properties or land use were found. GRSP extraction was decreased about seven‐fold by air‐drying of soils, confirming the irreversible change in the soil microstructure of allophanic soils. Total and easily extractable GRSP were correlated and we conclude that both are good probes of thermo‐stable soil protein content for these soils. No attempt was made to verify the fungal origin of the protein detected.

Microstructural development in volcanic ash soils from South Chile

Streaming potential measurements and amplitude sweep tests were performed on a range of Andosols from South Chile to find out about aggregation strength and mechanisms, as well as thixotropy and microstructural stability. Different stages in soil development and types of land use (pasture vs. natural forest) were considered and compared. Younger, alu-andic Andosols along with Al-humus-complexes contained higher levels of volcanic glass, indicated by their low pH values (pHH2O<5), and high ratios of sodium pyrophosphate extractable Al (Alp) to acid ammonium oxalate extractable Al (Alo) (Alp/Alo>0.5). Alu-andic Andosols were also found to have (super)hydrophobicity in addition to typically high contents of amorphous iron (ferrihydrite). On the contrary, in well-developed, sil-andic Andosols (Alp/Alo<0.5), allophane contents increased, accompanied by higher pH values (pHH2O>5 and <7). Based on rheological data, the gel–sol–gel transformation (thixotropy) was better defined in sil-andic Andosols. Integral z, a dimensionless rheological parameter that represents quasi-elasticity was used to quantify stiffness degradation, and to identify single stages of thixotropy in allophanic Andosols. Scanning electron micrographs revealed that mineralogical components were predominated by volcanic glass (e.g. vesicular) and amorphous iron oxides in addition to fungal hyphae in younger acidic Andosols, while these characteristics were absent in well-developed Andosols. Here weathered minerals e.g. biotite, as well as halloysite, (proto)imogolite and allophanes were identified, indicating desilication and a shift from alu-andic to sil-andic Andosols. Zeta potentials derived from conducted particle charge density (PCD) measurements supported the assumptions that (i) Al-humus-complexes promoted aggregation in partially superhydrophobic topsoils of alu-andic Andosols, especially at ungrazed sites (or 1 year under pasture), and that (ii) thixotropic behaviour is related to allophanic, sil-andic Andosols, and better pronounced at sites which had been under pasture for 50 years.

Erratum to ‘Are organo-mineral complexes and allophane content determinant factors for the carbon level in Chilean volcanic soils?’ [CATENA 92C (2012) 106–112

Erratum to ‘Are organo-mineral complexes and allophane content determinant factors for the carbon level in Chilean volcanic soils?’ [CATENA 92C (2012) 106–112

Sequestration of chlordecone in the porous structure of an andosol and effects of added organic matter: an alternative to decontamination

The context of this study is the pollution of soils and water by a persistent organo‐chlorinated insecticide, chlordecone, in a tropical environment. The application of chlordecone to control the banana black weevil has led to continuing diffuse pollution of soils, and to its being a source of contamination for cultivated plants, as well as for terrestrial and marine ecosystems. Chlordecone is toxic and stable and is considered to be a persistent organic pesticide. Consequently, the amounts of chlordecone that could migrate through the environment and contaminate agricultural products need to be controlled. We measured the impact of two composts (5% weight) on chlordecone sequestration in andosols. To this end, we first characterized the transfer of chlordecone from soil to water, and then its transfer from soil to plants. After 3 months of maturation, soil‐water and soil‐plant transfers were reduced by a factor of from 3 to 10. We also showed that adding compost to contaminated soils increases chlordecone sequestration because it leads to changes in soil microstructure in the form of pore collapse and closure of the fractal structure of the allophane content.