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Active Al, Fe and Si (i.e., oxalate extractable fraction: Alo, Feo, Sio) strongly affect soil physical, chemical and biological properties. This study examined the pedogenic factors affecting Alo, Feo and Sio contents across a soil weathering sequence in the Cameroon volcanic line. We investigated the B horizon (∼50-cm depth) from 26 soils formed in basaltic materials at different elevations (110–2570 m) incorporating a wide range of temperature (14–27 °C) and precipitation (1520–3130 mm). The weathering sequence ranged from weakly weathered Andisols in the southwest region grading to strongly weathered Oxisols on the central highlands. We assumed pyrophosphate extractable Al/Fe (Alp/Fep) as organo-Al/Fe complexes, and Sio, (Alo − Alp) and (Feo − Fep) as short-range-order (SRO) minerals. Factor analysis of climatic (e.g., temperature and precipitation/leaching metrics) and soil geochemical properties (e.g., weathering indices) identified three independent factors representing temperature/dry season intensity, weathering degree and precipitation/leaching as the primary determinants of Alo, Feo and Sio concentrations. Organo-metal complexes (Alp and Fep) were negatively correlated with the temperature/dry season intensity factor, whereas the SRO mineral phases (Sio, Alo − Alp and Feo − Fep) were negatively correlated with weathering degree. The precipitation/leaching factor positively correlated with Alo, Feo and Sio. Our analysis infers that low temperature promotes the formation and preservation of organo-Al/Fe complexes, whereas weathering degree is more critical for SRO minerals. Further, increased weathering and a drier climate enhance the formation of crystalline clay minerals at the expense of SRO minerals. Allophanic materials (Sio) were evident (Sio: 9–43 g kg−1) only in weakly weathered soils. However, low allophanic contents were found in more highly weathered soils (Sio: 2–7 g kg−1) accompanied by high Alp and Fep, suggesting the importance of volcanic parent materials as a direct source of Al and Fe via weathering for the formation of organo-metal complexes. In sum, we clarified the discriminatory effects of climatic factors and degree of weathering in regulating the composition of the active Al, Fe and Si fractions along the Cameroon volcanic line.

The objective of this study was to investigate the current soil properties in lowland paddy fields in Peninsular Malaysia and to assess the long-term changes in the soil fertility status during 50 ...

Understanding of the long-term soil fertility trends is the basis for rational and sustainable management of the soil resources in agricultural fields. In tropical Asia, the Green Revolution initia...

To examine the exchangeability of 137Cs and K in soils of agricultural fields after decontamination, 173 soil samples were collected in 2016 from the plowed layer (0–15 cm depth) of decontaminated agricultural fields in Tomioka town, Fukushima prefecture, Japan. We investigated total 137Cs, exchangeable 137Cs, exchangeable K, and nonexchangeable K content for these soils. The total 137Cs content in soils was, on average, 1,200 Bq kg−1 (value range: 20–4,400 Bq kg−1), which was an 80% decrease from the values determined before the decontamination. This result indicated that the decontamination process considerably reduced the total 137Cs content in the plowed layer. The exchangeable K content in soils was on average 172 mg kg−1 (value range: 27.9 – 743 mg kg−1). More than 80% of soils showed the exchangeable K content lower than the recommended threshold value for paddy soils needed in order to reduce the 137Cs transfer from soil to plant (i.e. 200 mg kg−1). The nonexchangeable K content showed a w...

Serpentine soils contain high levels of geogenic Cr and Ni, which may pose potential risks to the environment due to the increase of bioavailability of the metals during soil weathering. This study determined the lability of Cr and Ni by sequential selective extraction (SSE) and illustrated its relationships to mineral composition and physicochemical properties of serpentine soils for eight pedons along a climate gradient including temperate, subtropical, and tropical regions in Austria, Japan, Taiwan, and Indonesia. Although the mineral origin of Cr was different from that of Ni, Cr significantly accompanied Ni in various climates. Geochemical Cr and Ni fractions (by SSE) followed the order: residual (F4) > Fe/Mn oxide (F2) > organic matter (F3) > acid soluble (F1). Soil properties associated with changes in climate/weathering state, including pH, organic carbon, exchangeable Ca/Mg, and dithionite-citrate-bicarbonate extractable Fe, correlated with all fractions of Cr and Ni. Individual and the sum of all labile pools (∑F1–F3) of Ni were much higher than those of Cr in all pedons. Cr and Ni associated with Fe/Mn oxides (F2) was higher in the tropical soils than in the temperate soils, while Cr and Ni associated with organic matter (F3) was higher in the temperate soils than in the tropical soils along this gradient. Our results demonstrate that Cr and Ni are gradually transformed into labile pools in the soils as chemical weathering progresses from temperate to tropical climate.

Radiocesium (RCs) is selectively adsorbed on interlayer sites of weathered micaceous minerals, which primarily controls the mobility of RCs in the soil environment. Pedogenesis under acidic condition (under wetter climate regime) implies that RCs adsorption sites may be covered with soil organic matter (OM) and/or intercalated with hydroxy-Al polymer (Al(OH)x). While these interactions well-known control RCs adsorption, the relative importance of the two processes is virtually unstudied in field environment. We hypothesized that Al(OH)x intercalation plays dominant role in the adsorption inhibition in both surface and subsurface soils because Al(OH)x has more direct effect on RCs access to frayed edge site (FES), the sites intermediate between an expansible and non-expansible interlayers. Soils from two forest soil profiles under temperate and tropical climate (Ono, Japan and Kinabalu, Malaysia) were sampled every 3 cm from 0 to 30 cm and sieved to isolate soil particles of ≤ 20 μm diameters for the analysis of radiocesium interception potential (RIP) after a series of pretreatment. One subset was treated with H2O2 to remove OM. Another subset was further treated with hot sodium citrate to remove Al(OH)x after the H2O2 treatment. The changes in specific surface area (SSA) by the N2-BET method before and after the OM removal were determined to assess OM coverage on soil mineral surfaces. The contributions of OM removal to the total increase in RIP were surprisingly high (74.5–93.8%) in the uppermost soil layers (0–3 cm), implying that (i) OM reduced the access of RCs to FES, and (ii) OM binding with Al (organo‑aluminum complexation) reduced Al(OH)x formation in the interlayers. Towards deeper layers, OM contribution progressively declined to 2.4–13.9% whereas the Al(OH)x effect increased up to 86.1–97.6% in both profiles. The highest OM coverage on mineral surface (83.7%) was observed in the uppermost soil layer of Ono series. The stepwise OM removal of this sample by a weaker oxidizing reagent (NaOCl) for 6, 12, 24, and 30 h led to a gradual decline in OC content from 145 g kg− 1 to 67.2 g kg− 1. The OC losses were accompanied by a slight but progressive liberation in SSA from 8.3 to 12.2 m2 kg− 1, indicating that a portion of the soil mineral surfaces became exposed. However, RIP did not largely increase after the NaOCl treatment up to 30 h but remained quite low relative to the RIP value after the more complete OM removal by H2O2. These results indicate that the fraction of OM relatively resistant to chemical oxidation (presumably strongly bound to reactive portions of mineral surface) appeared to contribute to the inhibition of RCs adsorption on 2:1 interlayer sites. In conclusion, the ability of weathered micaceous minerals to retain RCs was largely reduced by two different mechanisms: OM coverage on the mineral surface (esp. at surface) and Al(OH)x interlayering (esp. at subsurface soil layers). Our results imply that long-term RCs dynamics may be strongly controlled by soil carbon level and thus ecosystem carbon balance (e.g., forest and grassland vs. bare and cropland) as well as the abundance and/or weathering degree of micaceous minerals.

The nonexchangeable potassium (neK) content of 178 agricultural soils in Japan was determined by subtracting the amount of K extracted with 1 mol L−1 ammonium acetate, i.e., exchangeable K ...

Radiocesium (RCs) is selectively adsorbed on weathered micaceous minerals (mica) in soils. Although it is clear that weathered mica has selective adsorption sites for RCs, which have been called ‘f...

Secondary mineral distributions in soils from Kalimantan, Indonesia, were investigated to examine the effects of the parent materials and climate at different elevations on the distributions. B horizon soils were sampled at 60 sites on gentle slopes at different elevations (20–1700 m altitude). Each major parent material (sedimentary, felsic, and intermediate to mafic) was represented at different elevations. The soil samples were classified from their total elemental compositions using cluster analysis. Secondary minerals were measured by X-ray diffraction and selective extractions. The samples were divided into ferric (high Fe contents), K&Mg (high K, Mg, and Si), and silicic (high Si) groups. The ferric soils were derived from mafic parent materials, whereas the others were derived from felsic or sedimentary parent materials. The K&Mg soils had higher total base contents (suggesting primary minerals) and were less weathered than the silicic soils. Secondary minerals in the ferric soils were characterized by high contents of Fe oxides and gibbsite. The K&Mg and silicic soils had similar secondary mineral (kaolinite and vermiculite) contents, but more mica was found in the former. Only the silicic group soils had secondary mineral contents that changed as the elevation changed (the kaolinite content increased and the vermiculite and poorly crystalline Al and Fe contents decreased as the elevation decreased). Higher temperatures at lower elevations may cause minerals to be altered more. Secondary mineral distributions were primarily controlled by the parent material (mafic or felsic/sedimentary) and, secondarily by the climate, which varied with elevation.

Land use intensity in the Cameroon plateaus, where Ferralsols and the associated highly weathered soils are dominant, has been steadily increasing, so that soil fertility status and its controlling factors on these plateaus should be elucidated to establish long-term land management strategies. Although it is known that Ferralsols have small, but variable CEC values, it has not been fully determined which clay components are the main source of CEC clay in Ferralsols. Here, soils in three Cameroon plateau regions of different altitude (the lower South Cameroon (SC) Plateau with an altitude of 300–600 m, SC L ; the upper SC Plateau with an altitude of 600–900 m, SC H ; and the Adamawa Plateau with an altitude above 900 m, ADM) were collected, and their physicochemical and mineralogical properties were investigated. The relative abundance of illitic minerals, which are a minor but the most promising source of CEC clay in Ferralsols, was determined by using three indicators: the relative abundances of 1.0 nm-thick structures as represented by XRD peak intensity (XRD 1.0 nm ), structural K in illitic minerals as represented by clay-K content, and the quantity of intermediate interlayer sites between illite and vermiculite structures (i.e., frayed edge sites) as represented by the radiocesium interception potential (RIP). The relative abundances of two low-activity clay components, kaolinite and gibbsite, were determined by differential thermal analysis, and the degree of Al-substitution in goethite was determined by differential x-ray diffraction analysis. All three quantitative indicators for illitic minerals decreased along the altitude gradient, SC L > SC H > ADM, and were positively correlated with CEC clay . While kaolinite also showed a decreasing trend at higher altitude, it did not show any significant correlation with CEC clay . In contrast to the decrease in these Si-bearing minerals, gibbsite and Al-substituted goethite increased along the same altitude gradient. These associative changes strongly indicate that illitic minerals were the clay component largely controlling CEC clay and that de-silication or aluminization may proceed at higher altitude or on stable surfaces with older formation ages in the Cameroon plateau regions. Thus, mineralogical properties well explained the distribution of Ferralsols; they were marginal in the SC L region, while those with relatively high CEC clay were dominant in the SC H region and those with lower CEC clay were dominant in the ADM region.

To evaluate the available silicon (Si) content in agricultural soils in Japan and to investigate the determining factors of this content, we collected 180 soil samples from the surface layer of paddies and upland fields in Japan and determined their available Si contents. A phosphate buffer (PB; 0.02 M, pH 6.9) or an acetate buffer (AB; 0.1 M, pH 4.0) was used to extract available Si from the soil samples, and the Si concentrations in the extracts were determined by inductively coupled plasma-atomic emissions spectroscopy (ICP-AES). The total Si content and selected physicochemical properties were also determined for the soil samples. The median values of the available Si contents by the PB and AB methods were 48.8 and 79.7 mg kg−1 and corresponded to 0.017% and 0.027% of the total Si content, respectively. The overall data showed log-normal distributions. The available Si content of the upland soils was significantly higher than that of the paddy soils by both the PB (p

The Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident in March 2011 resulted in the contamination of Japanese landscapes with radioactive fallout. Accordingly, the Japanese authorities decided to conduct extensive remediation activities in the impacted region to allow for the relatively rapid return of the local population. The objective of this review is to provide an overview of the decontamination strategies and their potential effectiveness in Japan, focussing on particle-bound radiocesium. In the Fukushima Prefecture, the decision was taken to decontaminate the fallout-impacted landscapes in November 2011 for the 11 municipalities evacuated after the accident (Special Decontamination Zone – SDZ – 1117 km2) and for the 40 non-evacuated municipalities affected by lower, although still significant, levels of radioactivity (Intensive Contamination Survey Areas, 7836 km2). Decontamination activities predominantly targeted agricultural landscapes and residential areas. No decontamination activities are currently planned for the majority of forested areas, which cover ∼75 % of the main fallout-impacted region. Research investigating the effectiveness of decontamination activities underlined the need to undertake concerted actions at the catchment scale to avoid renewed contamination from the catchment headwaters after the completion of remediation activities. Although the impact of decontamination on the radioactive dose rates for the local population remains a subject of debate in the literature and in the local communities, outdoor workers in the SDZ represent a group of the local population that may exceed the long-term dosimetric target of 1 mSv yr−1. Decontamination activities generated ∼20 million m3 of soil waste by early 2019. The volume of waste generated by decontamination may be decreased through incineration of combustible material and recycling of the less contaminated soil for civil engineering structures. However, most of this material will have to be stored for ∼30 years at interim facilities opened in 2017 in the vicinity of the FDNPP before being potentially transported to final disposal sites outside of the Fukushima Prefecture. Further research is required to investigate the perennial contribution of radiocesium from forest sources. In addition, the re-cultivation of farmland after decontamination raises additional questions associated with the fertility of remediated soils and the potential transfer of residual radiocesium to the plants. Overall, we believe it is important to synthesise the remediation lessons learnt following the FDNPP nuclear accident, which could be fundamental if a similar catastrophe occurs somewhere on Earth in the future.

Deposition of Asian dust, i.e. mica-bearing aeolian particles, throughout geological times has contributed greatly to the increased ability of soil to specifically retain radiocesium (137Cs), particularly in soils derived from mica-deficient parent materials. Allophanic Andosols, volcanic mica-deficient soils, in Japan were hypothesized to contain fewer micaceous minerals proximal to volcanoes due to the dilution of Asian dust by thicker volcanic ash depositions. To test this hypothesis, we collected soils from stratified horizons mainly composed of mafic volcanic ash at four sites near the volcanic crater of Mt. Aso, Japan. The profiles were in volcanic ash soil dominated by poorly ordered clay minerals, and classified as Allophanic Andosols. Radiocesium interception potential (RIP) and mineral content were determined on soil particles fractionated to

The radiocesium interception potential (RIP) of bulk soil (RIP) can reliably be used to predict the magnitude of soil-to-plant radiocesium transfer. There has been some controversy about which soil properties control the RIP, although the RIP is theoretically proportional to the amount of frayed edge sites in micaceous clay minerals. The RIP was determined for 97 paddy soils in three regions (Hama-dori, Naka-dori, and Aizu) in Fukushima Prefecture, Japan, and the relationships between selected physicochemical properties and the RIP were analyzed. The mean (± standard deviation) of the RIP for the 97 soils was 1.67 (±0.87) mol kg, and the range was 0.34 to 5.36 mol kg. Pearson correlation analysis revealed that the RIP positively correlated best ( < 0.01) with the clay fraction K content as a mass fraction of the bulk soil (clay-K) and negatively correlated with the total C content and the phosphate absorption coefficient ( < 0.05). Therefore, clay-K, an indicator of the amount of micaceous clay minerals in a soil, was confirmed as being useful for estimating the magnitude of the RIP for paddy soils in Fukushima. The RIP was invariably low if either the total C content exceeded 6.0% or the phosphate absorption coefficient exceeded 1500 mg kg, suggesting that these parameters could be useful for screening soils with particularly low RIP values.

To evaluate the content of nitrogen (N) fractions of agricultural soils in Java, Indonesia, in relation to soil type and land use, 46 surface soil samples, 23 from paddy and 23 from upland, were collected throughout Java to include various types of soils. Soil N was separated into four fractions according to form and availability: inorganic extractable nitrogen (Iex-N), fixed ammonium nitrogen (Ifix-N), organic mineralizable nitrogen (Omin-N) and organic stable nitrogen (Osta-N). The total-N content was determined by the dry combustion method. The Iex-N content was determined by extraction with a 2 mol L−1 potassium chloride (KCl) solution and the Ifix-N content by extraction with an hydrofluoric and hydrochloric acid (HF-HCl) solution after removal of organic-N. The Omin-N content was evaluated as the potentially mineralizable N based on a long-term incubation method. The Osta-N content was calculated as the difference between the contents of total-N and the three other fractions. The total-N con...

Although it is well known that phytoavailability of radiocaesium is gradually lost after its deposition on the ground by fixation to soil minerals, the decreasing rates during early period after the deposition is not yet quantitatively evaluated. In this study, stable Cs was added to 5 types of soil, including Andosols, a sand-dune regosol and a smectic lowland soil, in a laboratory soil incubation experiment to assess the aging effect of radiocaesium. Aliquots of a soil sample were put into pots and incubated in an artificial climate chamber. Orchardgrass or red clover was cultivated for 28 d in soil pots containing one of the allophanic Andosol samples seven times during about 1200 d using new pots for each cultivation. The soil-to-plant transfer factors of Cs declined exponentially until about 100 d and were almost constant thereafter. The extractabilities of Cs by water and 1 M NH4OAc solution from this allophanic Andosol soil sample also decreased with time and their decreasing patterns were similar to that of the transfer factor. The temporal changes of extractabilities of Cs in other soil samples were also examined 6 times during about 600 d. Rate of decline for the extracted yield of the added Cs by 1 M NH4OAc varied widely among all the soil types. Two allophanic Andosol samples showed relatively higher extractabilities in comparison with the other soils throughout the incubation experiment, which may be attributable to the lower contribution of Cs specific sorption sites to total cation exchange capacity of the allophonic Andosol soil samples.

The distribution coefficient of cesium (Cs) (KdCs) was investigated for clays which were collected from upland forest soils developed from granites and Paleozoic shales in Japan. They were divided into three size fractions, coarse (2.0–1.0 µm), medium (1.0–0.2 µm), and fine-clay fractions (

Summary The transformation of hydroxy-interlayered vermiculite (HIV) to vermiculite in humid temperate soils may involve the gradual alteration of illitic minerals. However, it is difficult to detect such minor and progressive changes using conventional methods. We measured the amount of the frayed edge site (i.e. the weathering front of illitic minerals) in soil clays using Radiocaesium Interception Potential (RIP) methodology, and elucidated the effect of hydroxy-Al polymers on the frayed edge site that may be occluded within HIV structures in the acidic soils of southwestern Japan. X-ray diffraction patterns showed the progressive transformation of HIV to vermiculite, or further, to smectite in soil clays located in upper horizons and therefore subjected to more intensive podzolization. In this process, the amount of hydroxy-Al polymers (represented by hot-citrate Al) gradually decreased, while the vermiculitic charges increased (represented by Cs-fixing capacity). However, the amount of the frayed edge site (represented by the RIP) firstly increased but then reversed and decreased in the upper layers of podzolic soils. After hot-citrate extraction to remove the hydroxy-Al polymers from HIV, the amount of the frayed edge site increased in HIV-dominated clays, whereas there was a negligible increase in vermiculitic- or smectitic-clays, thus indicating the blockage effect of hydroxy-Al polymers on the frayed edge site. The sequential increase followed by the decrease that we documented in the amount of the frayed edge site along with the HIV-vermiculite-smectite transformation, suggested that the weathering front of illitic minerals was exposed as the HIV layers lose hydroxy-Al polymers. Thereafter, the charges in the exposed frayed edge site might decline under the very acidic conditions of the upper layers of podzolic soils.

Summary A frayed edge site can be a significant indicator of alterations in illitic minerals in soils evolving under different climates, because illitic minerals are known to enlarge the frayed edge site through vermiculitization. We investigated the relative abundance of this site in soil clays (

Radiocesium interception potential (RIP), a quantitative index of a frayed edge site of micaceous minerals, was investigated on test clay minerals (illite, kaolinite, montmorillonite and vermiculit...