Non-allophanic Soils Research Articles

New definition of the qualifiers for Dystric and Eutric should be noted for the classification of Andosols with WRB2014

ABSTRACT The WRB (World Reference Base for Soil Resources) 2014 adopted ‘effective base saturation (EBS),’ which is the ratio of exchangeable bases (Ca + Mg + K + Na) to effective CEC (Ca + Mg + K + Na + Al), instead of base saturation (BS), the ratio of exchangeable bases to the cation exchange capacity, as the criterion for the addition of qualifiers concerning the condition of exchangeable bases. An EBS of less than 50% was defined as Dystric conditions, and that of 50% or more was defined as Eutric conditions. These newly defined qualifiers were applied to 49 soil samples from grasslands of Andosols in central Kyushu and 132 horizons from a database of Japanese Andosols. It was found that 80% of the samples met the criterion for Eutric conditions according to WRB2014, despite their small amount of exchangeable bases and low BS, whereas only 2% were Eutric when the criterion of WRB2006 (BS ≥ 50%) was used. In the case of uncultivated soils, the definitions of Dystric and Eutric according to WRB2014 corresponded mainly to non-allophanic and allophanic soils, respectively. All pedons of allophanic Andosols were classified as Eutric, but those of non-allophanic Andosols were classified as Dystric, according to WRB2014, because of the high EBS recorded in them. Conversely, all pedons were classified as Dystric based on the WRB2006 criteria. These characteristics of the Dystric and Eutric qualifiers in the classification of Andosols according to WRB2014, which is related to the variable charge of the samples, should be noted for the proper understanding and management of base conditions of Andosols.

Patterns in Soil Chemical Weathering Related to Topographic Gradients and Vegetation Structure in a High Andean Tropical Ecosystem

AbstractAlthough climate exerts a major control on mineral weathering and soil formation processes, the combined effect of vegetation and topography can influence the rate and extent of chemical weathering at the hillslope scale. In this paper, we examined spatial patterns in volumetric strain and soil weathering extent associated with topographic gradients and vegetation patterns. In a high Andean catchment, we selected 10 soil toposequences on andesitic flows: 5 under tussock grasses, 3 under cushion forming plants, and 2 under native forest. Along each toposequence, one pit was excavated at the shoulder, backslope, and toeslope resulting in 30 soil profiles. Depth‐weighted total soil porosity of the 30 soil profiles averaged 64 ± 6%. The association between volumetric strain and soil organic C indicates that biotic agents can be effective in dilating the regolith during weathering. The young, postglacial volcanic soils were depleted in mono‐divalent and divalent cations, with total mass losses ranging between 793 and 1610 kg/m2. The accumulation of Al‐humus complexes in the soil matrix plays an essential role in chemical transformation of the nonallophanic soils. Beyond the marginally significant topographic control on chemical weathering extent, our data show highly significant differences in chemical weathering extent between vegetation communities with total mass losses in forest soils being, respectively, 19% and 22% higher than in grasslands and cushion‐forming plants. The vegetation mosaic in alpine ecosystems might therefore provide essential clues to understand soil chemical weathering patterns caused by spatially varying soil particle and water residence times.

An investigation of organic matter quality and quantity in acid soils as influenced by soil type and land use

Knowledge of the molecular composition of soil organic matter (OM) and the interaction of OM with soil minerals is needed to fundamentally understand how the persistence of OM is affected by land use. We investigated organic carbon (C) fractions, content of short-range order constituents (SRO) (i.e., Al and Fe oxy-hydroxides) and OM chemistry of 45 top soils across a range of soil orders and land uses in New Zealand. The objective of the study was to assess the influence of different land uses on the OM quality and quantity of soils that differed in their content of SRO constituents. The C fractions considered were cold + hot water-soluble C (CH2O), C recovered in the residuum after HF treatment (CHF-residuum), and C not so recovered (CHF-mobile). Carbon in particulate OM (CPOM) was determined in non-Allophanic soils, and C extractable with sodium pyrophosphate (Cp) in Allophanic soils. The chemistry of the HF-residual OM was investigated using pyrolysis-GC/MS. The highest C content was found under grazed grasslands and, among soil orders, in Allophanic soils, which had the largest CHF-mobile and CHF-residuum contents. Yet compared to non-Allophanic, Allophanic soils were more vulnerable to loss of C (CHF-mobile and CHF-residuum) when used for cropping. The relative contribution of microbial- vs. plant-derived OM was influenced by soil order and land use: microbial-derived OM increased as the presence of SRO constituents increased, these being more abundant in Allophanic soils; soils under ungrazed grasslands had the largest contribution of fresh plant-derived molecules to OM (and of CHF-residuum to total C) while cropping had a negative impact on the contribution of plant-derived OM, consistent with a decrease in CPOM. Overall, the results showed that not only is the ability of New Zealand soils to store C soil-specific, but so too is their vulnerability to losing it when under specific land use.

Soil carbon sequestration potential of permanent pasture and continuous cropping soils in New Zealand.

Understanding soil organic carbon (SOC) sequestration is important to develop strategies to increase the SOC stock and, thereby, offset some of the increases in atmospheric carbon dioxide. Although the capacity of soils to store SOC in a stable form is commonly attributed to the fine (clay+fine silt) fraction, the properties of the fine fraction that determine the SOC stabilization capacity are poorly known. The aim of this study was to develop an improved model to estimate the SOC stabilization capacity of Allophanic (Andisols) and non-Allophanic topsoils (0-15cm) and, as a case study, to apply the model to predict the sequestration potential of pastoral soils across New Zealand. A quantile (90th) regression model, based on the specific surface area and extractable aluminium (pyrophosphate) content of soils, provided the best prediction of the upper limit of fine fraction carbon (FFC) (i.e. the stabilization capacity), but with different coefficients for Allophanic and non-Allophanic soils. The carbon (C) saturation deficit was estimated as the difference between the stabilization capacity of individual soils and their current C concentration. For long-term pastures, the mean saturation deficit of Allophanic soils (20.3mg C g-1 ) was greater than that of non-Allophanic soils (16.3mg C g-1 ). The saturation deficit of cropped soils was 1.14-1.89 times that of pasture soils. The sequestration potential of pasture soils ranged from 10t C ha-1 (Ultic soils) to 42t C ha-1 (Melanic soils). Although meeting the estimated national soil C sequestration potential (124Mt C) is unrealistic, improved management practices targeted to those soils with the greatest sequestration potential could contribute significantly to off-setting New Zealand's greenhouse gas emissions. As the first national-scale estimate of SOC sequestration potential that encompasses both Allophanic and non-Allophanic soils, this serves as an informative case study for the international community.

Soil Type and Growing Conditions Influence Uptake and Translocation of Organochlorine (Chlordecone) by Cucurbitaceae Species

Chlordecone (CLD), an organochlorine insecticide, and other persistent organic pollutants continue to contaminate the environment worldwide and have adverse effects on human health through food exposure. Cucurbitaceae take up weathered hydrophobic pollutants from the soil and translocate them to their shoots. As Cucurbitaceae are an important part of the diet in the French West Indies, they are among the main contributors to total dietary intake of CLD. We analyzed the contamination by CLDs (CLD and 5b-hydroCLD) of four cucurbits grown in the field and/or in the greenhouse. Different physiological (crop species) and environmental (soil type, growth conditions) variables were shown to influence uptake of the pollutant from the soil by the crop. Cucurbita species (zucchini and pumpkin) were more contaminated than Cucumis sativus (cucumber), and Sechium edule (christophine or chayote) translocated CLDs to fruits very poorly compared with cucumber and pumpkin. Greenhouse conditions and non-allophanic (nitisols and ferralsols) soils favored plant contamination more than field conditions and allophanic soils (andosols).

Estimating the organic carbon stabilisation capacity and saturation deficit of soils: a New Zealand case study

The capacity of a soil to sequester organic carbon can, in theory, be estimated as the difference between the existing soil organic C (SOC) concentration and the SOC saturation value. The C saturation concept assumes that each soil has a maximum SOC storage capacity, which is primarily determined by the characteristics of the fine mineral fraction (i.e. 0. The median saturation deficit for both Allophanic and non-Allophanic soils was 12 mg C g−1 at 0–15 cm depth and 15 mg C g−1 at 15–30 cm depths. Improving predictions of the saturation deficit of soils may be important to developing and deploying effective SOC sequestration strategies.

Bioavailability and ecotoxicity of arsenic species in solution culture and soil system: implications to remediation

In this work, bioavailability and ecotoxicity of arsenite (As(III)) and arsenate (As(V)) species were compared between solution culture and soil system. Firstly, the adsorption of As(III) and As(V) was compared using a number of non-allophanic and allophanic soils. Secondly, the bioavailability and ecotoxicity were examined using germination, phytoavailability, earthworm, and soil microbial activity tests. Both As-spiked soils and As-contaminated sheep dip soils were used to test bioavailability and ecotoxicity. The sheep dip soil which contained predominantly As(V) species was subject to flooding to reduce As(V) to As(III) and then used along with the control treatment soil to compare the bioavailability between As species. Adsorption of As(V) was much higher than that of As(III), and the difference in adsorption between these two species was more pronounced in the allophanic than non-allophanic soils. In the solution culture, there was no significant difference in bioavailability and ecotoxicity, as measured by germination and phytoavailability tests, between these two As species. Whereas in the As-spiked soils, the bioavailability and ecotoxicity were higher for As(III) than As(V), and the difference was more pronounced in the allophanic than non-allophanic soils. Bioavailability of As increased with the flooding of the sheep dip soils which may be attributed to the reduction of As(V) to As(III) species. The results in this study have demonstrated that while in solution, the bioavailability and ecotoxicity do not vary between As(III) and As(V), in soils, the latter species is less bioavailable than the former species because As(V) is more strongly retained than As(III). Since the bioavailability and ecotoxicity of As depend on the nature of As species present in the environment, risk-based remediation approach should aim at controlling the dynamics of As transformation.

Phosphorus–arsenic interactions in variable-charge soils in relation to arsenic mobility and bioavailability

Phosphorus (P) influences arsenic (As) mobility and bioavailability which depends on the charge components of soil. The objective of this study was to examine P–As interaction in variable-charge allophanic soils in relation to P-induced As mobilization and bioavailability. In this work, the effect of P on arsenate [As(V)] adsorption and desorption was examined using a number of allophanic and non-allophanic soils which vary in their anion adsorption capacity. The effect of P on As uptake by Indian mustard (Brassica juncea L.) plants was examined using a solution culture, and a soil plant growth experiment involving two As-spiked allophanic and non-allophanic soils which vary in their anion adsorption capacity, and a field As-contaminated sheep dip soil. Arsenate adsorption increased with an increase in the anion adsorption capacity of soils. The addition of P resulted in an increase in As desorption, and the effect was more pronounced in the case of allophanic soil. In the case of both As-spiked soils and field contaminated sheep-dip soil, application of P increased the desorption of As, thereby increasing its bioavailability. The effect of P on As uptake was more pronounced in the high anion adsorbing allophanic than low adsorbing non-allophanic soil. In the case of solution culture, As phytoavailability decreased with increasing concentration of P which is attributed to the competition of P for As uptake by roots. While increasing P concentration in solution decreased the uptake of As, it facilitated the translocation of As from root to shoot. The net effect of P on As phytoavailability in soils depends on the extent of P-induced As mobilization in soils and P-induced competition for As uptake by roots. The P-induced mobilization of As could be employed in the phytoremediation of As-contaminated sites. However, care must be taken to minimize the leaching of As mobilized through the P-induced desorption, thereby resulting in groundwater and off site contamination.

Sorption–bioavailability nexus of arsenic and cadmium in variable-charge soils

In this work, the nexus between sorption and bioavailability of arsenic (As) and cadmium (Cd) as affected by soil type, soil pH, ageing, and mobilizing agents were examined. The adsorption of As and Cd was examined using a number of allophanic and non-allophanic soils which vary in their charge components. The effect of pH and ageing on the bioavailability of As and Cd was examined using spiked soils in a plant growth experiment. The effect of phosphate (P)-induced mobility of As on its bioavailability was examined using a naturally contaminated sheep dip soil. The results indicated that the adsorption of both As and Cd varied amongst the soils, and the difference in Cd adsorption is attributed to the difference in surface charge. An increase in soil pH increased net negative charge by an average of 45.7mmol/kg/pH thereby increasing cation (Cd) adsorption; whereas, the effect of pH on anion (As) adsorption was inconsistent. The bioavailability of As and Cd decreased by 3.31- and 2.30-fold, respectively, with ageing which may be attributed to increased immobilization. Phosphate addition increased the mobility and bioavailability of As by 4.34- and 3.35-fold, respectively, in the sheep dip soil. However, the net effect of P on As phytoavailability depends on the extent of P-induced As mobilization in soils and P-induced competition for As uptake by roots. The results demonstrate the nexus between sorption and bioavailability of As and Cd in soils, indicating that the effects of various factors on bioavailability are mediated through their effects on sorption reactions.

Use of shallow samples to estimate the total carbon storage in pastoral soils

Using data from pastoral soils sampled by horizon at 56 locations across New Zealand, we conducted a meta-analysis. On average, the total depth sampled was 0.93±0.026 m (± SEM), and on a volumetric basis, the total C storage averaged 26.9±1.8, 13.9±0.6 and 9.2±1.4 kg C m−2 for allophanic (n=12), non-allophanic (n=40) and pumice soils (n=4), respectively. We estimated the total C storage, and quantified the uncertainty, using the data for samples taken from the uppermost A-horizon whose depth averaged 0.1±0.003 m. For A-horizon samples of the allophanic soils, the mean C content was 108±6 g C kg−1 and the bulk density was 772±29 kg m−3, for non-allophanic soils they were 51±4 g C kg−1 and 1055±29 kg m−3, and for pumice soils they were 68±9 g C kg−1 and 715±45 kg m−3. The C density—a product of the C content and bulk density—of the A-horizon samples was proportional to their air-dried water content, a proxy measure for the mineral surface area. By linear regression with C density of the A-horizon, the total C storage could be estimated with a standard error of 3.1 kg C m−2, 19% of the overall mean.

Chlordecone retention in the fractal structure of volcanic clay

Chlordecone (CHLD), a soil and foodstuff pollutant, as well as an environmentally persistent organochlorine insecticide, was used intensively in banana fields. The chlordecone uptake of three crops was measured for two types of polluted soils: allophanic and non-allophanic. The uptake is lower for allophanic soils even if their chlordecone content is higher than with non-allophanic soils. The fractal structure of the allophane aggregates was characterized at the nanoscale by small angle X-rays scattering, pore size distribution and transmission electron microscopy. We showed that clay microstructures should be an important physico-chemical factor governing the fate of chlordecone in the environment. Allophanic clays result in two counterintuitive findings: higher contaminant trappings yet lower contaminant availability. We propose that this specific, tortuous structure, along with its associated low accessibility, partly explains the low availability of chlordecone confined in allophanic soils.CapsuleThe fractal and tortuous microstructure of allophane clay favours the chlordecone retention in soils and disfavours the crop uptake.

Path Analysis of Phosphorus Retention Capacity in Allophanic and Non-allophanic Andisols

Andisols derived from volcanic ash minerals are characterized by a high P retention capacity (PRC). The PRC of soil is often correlated with various soil properties, and a simple correlation analysis alone may not necessarily explain the direct cause and effect relationships between soil properties and PRC values. The objectives of this study were to determine which soil properties best explain the variability in the PRC of allophanic and non-allophanic Andisols using path analysis. A total of 671 Japanese Andisols were used in this study. The PRC values were determined for allophanic and non-allophanic soil samples, along with pH, organic matter (OM) contents, acid ammonium oxalate extractable Al (Al ox ) and Fe (Fe ox ), and pyrophosphate-extractable Al (Al p ) and Fe (Fe p ). The PRC value of allophanic soils was correlated with Al ox (r = 0.72) and Fe ox (r = 0.56). Path analysis revealed, however, that Al ox was the single most important direct effect on PRC, and the correlation between PRC and Fe ox was mostly partitioned to an indirect effect through Al ox . According to path analysis on non-allophanic soils, Al p was the single most important causal factor in predicting PRC, and the correlation between Al ox and PRC (r = 0.77) was mostly partitioned to an indirect effect through Al p . The correlation between OM and PRC was attributable to organically bound Al in allophanic soils by the indirect effect of Al p on PRC through OM. Pyrophosphate extraction may be a better indicator than oxalate extraction for predicting PRC in non-allophanic Andisols.

Inhibitory effect of acid Andosols on plants – is aluminum toxicity true for allophanic Andosols?

Non-allophanic Andosols often show aluminum (Al) toxicity to Al-sensitive plant roots. The toxicity was evaluated by the 1 M potassium chloride (KCl)-extractable Al (AlKCl) content. In contrast, natural allophanic Andosols rarely show any Al toxicity, whereas AlKCl can appear with strong acidification. It is still not clear whether the acidic allophanic soils cause the Al toxicity, or the acid injury in Andosols is totally explained by the Al toxicity. In this study, plant cultivation experiments were performed using non-allophanic and allophanic soils over a wide-range of pH values; two typical non-allophanic soils [pH(H2O) 4.4–4.7], their limed soils [pH(H2O) 5.9–6.1], two typical allophanic soils [pH(H2O) 5.7–7.0], three acidic allophanic soils [pH(H2O) 4.6–5.4] and a commercial Kanuma pumice. We cultivated the Al-sensitive plants [burdock (Arctium lappa L.) and barley (Hordeum vulgare)] and an Al-accumulative plant [buckwheat (Fagopyrum esculentum)] in these soil samples, then measured the root lengths of the burdock and barley and determined the Al concentrations in the buckwheat. The toxic (available) Al was evaluated from the results of these cultivations. The typical non-allophanic soils showed a strong inhibition of the roots of the burdock and barley. Although the inhibition was not observed in the typical allophanic soils for the Al-sensitive plants, the acidic allophanic soils did show the inhibition as observed in the non-allophanic soils. Close negative correlations were observed between the root lengths of the Al-sensitive plants and the Al concentrations in the buckwheat (P < 0.05); the Al concentrations in the buckwheat grown in the non-allophanic soils were much higher (2.6–4.3 mg g−1) than those in the typical allophanic soils (0.4–1.4 mg g−1), and these concentrations in the buckwheat in the acidic allophanic soils were comparable (2.7–4.0 mg g−1) to those in the non-allophanic soils. Thus, it was shown that the acid injury of the Andosols is definitely caused by the Al toxicity, regardless of the type of Andosols, i.e. non-allophanic or allophanic. Possible substances controlling the Al toxicity were discussed in relation to soil properties.

Phosphorus desorbability in soils with andic properties from the Azores, Portugal.

Desorbability of phosphorus (P des) at P sorption maxima in eighteen horizons (surface and subsurface) of soils with andic properties from the Azores, Portugal, was determined by eight successive extractions using distilled water (H2O), calcium chloride (CaCl2), Bray 2 (B2), Mehlich 3 (M3), Egner-Riehm (ER) and Olsen (OL) methods. The highest proportions of P des by the B2, M3, ER and OL methods (29-100%) were obtained in soils with weak andic properties (Vitrandic Haplustepts, Typic Haplustepts and Andic Haplustepts), indicating that P can be easily lost from these soils to nearby water bodies, through surface runoff and subsurface drainage. In contrast, low proportions of P des (4-57%) by these methods were obtained in allophanerich (Acrudoxic Hydrudands and Typic Placudands) and non-allophanic soils (Acrudoxic Hydrudands and Alic Hapludands), indicating that large amounts of P can be sorbed in an unavailable form by these soils. Of the six methods used, the proportions of P des obtained by H2O and CaCl2 were consistently lower than those obtained by the B2, M3, ER and OL methods. The proportion of P des obtained by the B2 method was highly correlated with other methods (M3, ER and OL) suggesting that the B2 is also an effective method to extract P in most of the studied soils. The proportions of P des obtained by different methods were negatively correlated with Feo and Fed, correlatios being stronger than with Alo, Ald, Alp and Fep contents. This indicates that Feo and Fed plays an important role in desorbability of P in studied soils.

Decomposition of dicyandiamide (DCD) in three contrasting soils and its effect on nitrous oxide emission, soil respiratory activity, and microbial biomass—an incubation study

The objective of this work was to study the degradation kinetics of a nitrification inhibitor (NI), dicyandiamide (DCD), and evaluate its effectiveness in reducing nitrous oxide (N2O) emissions in different types of soils. Three soils contrasting in texture, mineralogy, and organic carbon (C) content were incubated alone (control) or with urine at 600 mg N/kg soil with 3 levels of DCD (0, 10, and 20 mg/kg). Emissions of N2O and carbon dioxide (CO2) were measured during the 58-day incubation. Simultaneously, subsamples were collected periodically from the incubating soils (40-day incubation) and the amounts of DCD, NH4+, and NO3− were determined. Our results showed that the half-life of DCD in these laboratory incubating soils at 25°C was 6–15 days and was longer at the higher rate of DCD application. Of the 3 soils studied, DCD degradation was fastest in the brown loam allophanic soil (Typic orthic allophanic) and slowest in the silt loam non-allophanic soil (Argillic-fragic Perch-gley Pallic). The differences in DCD degradation among these soils can be attributed to the differences in the adsorption of DCD and in the microbial activities of the soils. Among the 3 soils the highest reduction in N2O emissions with DCD from the urine application was measured in the non-allophanic silt loam soil followed by non-allophanic sandy loam soil and allophanic brown loam soil. There was no adverse impact of DCD application on soil respiratory activity or microbial biomass.

Abstracts of Nippon Dojo-Hiryogaku Zasshi

Abstracts of Nippon Dojo-Hiryogaku Zasshi

2,4‐D Movement in Allophanic Soils from Two Contrasting Climatic Regions

Allophanic top‐ and subsoils from the Mexican and Newzealand Central Volcanic Plateau, as well as a nonallophanic sandy loam soil, were sampled to study the impact of organic matter and allophane content on 2,4‐D fate. High sorption rates were found, especially in the two topsoils from Mexico and New Zealand, with distribution coefficient (K d ) obtained from displacement experiments in packed columns equal to 7.61 and 8.43 L kg−1 respectively. 2,4‐Dichlorophenoxyacetic acid transfer through the soil columns was found to be in chemical nonequilibrium and was well predicted using a two‐site sorption model. For the two allophanic top soils, K d obtained from batch was very different to the K d obtained from column experiments. Either the equilibrium could not be reached in batch or the two‐site model was not able to describe the wide range of sorption sites present in the highly reactive organic matter and allophane components.

Soil Chemistry Effect on Feasibility of Cr-decontamination by Acid-Washing

Soil washing with sirnple acid has been proven to be effective for removal of cationic heavy metals from contaminated soils. Since the adsorption of anionic heavy metals is enhanced in acidic medium, the efrrciency of acid-washing may not be guaranteed for soils that are doubly contaminated with cationic and anionic heavy metals. To evaluate the efficiency of acid-washing, nine soils were artificially contaminated with chromate and chromium was extracted with hydrochloric acid of 0.5mrnol L-* to I mol L-'. A part of spiked chromate was reduced to trivalent chromium and the remaining chromate ions were almost quantitatively extracted wlth the hydrochloric acid. However, increasing hydrochloric acid concentration was not effective for the extraction. Possible mechanisms underlying the observed low efficiency were considered to be the enhanced reduction in acidic solution, complexation by humic substance and adsorption via cation exchange reactions. We concluded that acid-washing satisfactorily works for chromate removal in non-allophanic soils but inefficient for removal of trivalent chromium particularly from soils having high effective cation exchange capacity and organic matter content.

Mineral Composition of Clay Fractions and Oxygen Vacancies in Silt-Sized Quartz in Soils on the Ka-Etsu Plateau, Fukui, Central Japan—Possibility of Eolian Dust Brought from Northern Asia as Parent Material of Soils

Fine- to medium-textured soils are distributed on the Early Pliocene rocks and Pleistocene sandy sediments in the Ka-Etsu plateau. The Jingaoka (JIN) soil was classified into Aluandic Andosols by WRB, and Low-humic Non-allophanic Kuroboku soils by the Fourth Committee for Soil Classification and Nomenclature of the Japanese Society of Pedology, although it was similar morphologically to Yellow-Brown Forest soils. On the other hand, the Tomitsu (TMI) and Yamamuro (YAM) soils were classified into Hyperdystri-Chromic Cambisols by WRB, and Typic Yellow-Brown Forest soils by the Fourth Committee for Soil Classification and Nomenclature based on the morphological, physical and chemical properties. These soils were influenced considerably by the Akahoya tephra, especially the JIN soil. Based on the results of clay-mineralogical analysis and the measurement of the ESR-signal intensity associated with the oxygen vacancies in fine quartz, a large part of parent materials in the soils distributed on the Ka-Etsu plateau was derived from the eolian dust which was brought with the NW winter monsoon from the Precambrian sediments in the northern part of the Asian continent during MIS 2 (24–11 thousand years ago) at the Last Glacial Maximum. The parent materials of the fine-textured JIN soil located on the highest terrace near the rocky coastline were mostly composed of eolian dust, although the influenced of the Akahoya tephra was recognized. The parent materials of the TMI soil were admixed with a small amount of autochthonous materials from the sandy coast located windward. In the YAM soil which was located on the side of a hilly area distant from the coastline, the ESR-signal intensity in fine quartz was considerably low, and the admixture of autochthonous materials was also considered since the texture of this soil was coarser than that of the JIN and TMI soils.

Clay mineralogy effects on sodium fluoride pH of non-allophanic tropical soils

Soil pH measured in 1 m NaF (pHNaF) can be a useful tool for soil classification and to provide better advice on the chemical management of agricultural soils in the tropics. In this study, we verified the effects of clay mineralogy on pHNaF values of non-allophanic soils of São Paulo State, Brazil. Fourteen subsurface soil samples were characterised for chemical properties, clay content, clay mineralogy, and for pHNaF values, which were measured in the whole soil and in both natural and deferrified (dithionite-treated) clay fractions. Regression and correlation analyses showed that both ammonium-oxalate-extractable Al (Alo) and gibbsite contents have positive relationships with both clay and soil pHNaF values. On the other hand, kaolinite is inversely related to the pHNaF measured in the clay and has nonsignificant effect on soil pHNaF. X-ray diffraction patterns of dithionite-treated clays did not show disruption of kaolinite or gibbsite after the treatment with 1 m NaF, suggesting that the displacement of surface OH groups by F– seems to be the main mechanism associated with the pH increase verified in the NaF solution after its contact with the deferrified clay fraction. The smaller influence of hematite on pHNaF seems to be due to its correlation to Alo. Goethite and ammonium-oxalate-extractable Fe (Feo) exert no effect on pHNaF. Finally, the relationships observed in the present study strongly suggest that pHNaF values &lt;10.3 measured in non-allophanic kaolinitic soils with low levels of non-humified organic matter are essentially due to their smaller Alo and gibbsite contents, which agrees with the direct correlation verified between pHNaF and soil weathering degree.