Andic properties in soils developed from nonvolcanic materials in Central Bhutan

A number of soils are described in the literature as having andic and spodic soil properties, but have developed in nonvolcanic and nonallophanic materials and lack typical Podzol eluvial and illuvial horizons. They cover a wide range of parent materials and different types of climate. They have always been regarded as restricted to small areas. They were assigned to Andisols/Andosols, Podzols/Spodosols, or andic Inceptisols in the WRB and Soil Taxonomy and sometimes also named Cryptopodzols or Lockerbraunerden. Recent soil surveys in Bhutan, E Himalayas, show these soils are widespread at altitudes between 2200–3500 m asl and are spanning several bioclimatic zones. The aim of this study is the detailed characterization of specific properties and processes of formation by physical and chemical analyses, NMR spectroscopy, column experiments, SEM, XRD, and ¹⁴C dating in one of these soils in E central Bhutan. The results indicate advanced soil development with high amounts of oxidic Fe and Al compounds, low bulk densities (partly <0.5 g cm^–3), P retention >85%, and a dominance of Al‐hydroxy‐interlayered phyllosilicates. Scanning electron microscopy of sand fractions indicate microaggregates highly resistant to dispersion. Column experiments show podzolization with mobilization and translocation of DOM, Fe, and Al. Nuclear‐magnetic resonance spectroscopy and ¹⁴C ages of 16,000 BP indicate stabilization of DOM. Applying classification criteria, these soils appear to have andic and spodic features, but are neither Andosols nor Podzols senso strictu. Especially the role of Fe seems to be underestimated with regard to the specific soil‐forming processes. Because of their widespread occurrence and distinct properties, we suggest either a simplification of the criteria for existing soil types or a clearly defined separation of volcanic and nonvolcanic/nonallophanic Andosols.     

Andosols of Georgia

Andosols formed on andesite-basalts, andesite, diabase, and dolerite in the central part of the Adzhar-Trialet Ridge are studied. Their morphological features and some chemical properties are characterized. The soils are diagnosed according to the World Reference Base for Soil Resources (WRB). The soil bulk density, the contents of oxalate-soluble R₂O₃, adsorbed phosphates, and organic carbon are determined. It is shown that vitric and andic diagnostic features predominate in the investigated soils. According to the adopted classification, these soils are classified as mountain meadow soils. Their morphological features and chemical characteristics correspond to those of Andosols, one of the soil groups in the WRB. It can be expected that these soils are developed in some other regions of volcanic activity in Georgia.     

The importance of andic soils in mountain ecosystems: a pedological investigation in Italy

Andic soils have unique morphological, physical and chemical properties that induce both considerable soil fertility and great vulnerability to land degradation. In recent years there have been many reports of soils with andic properties in Non‐Volcanic Mountain Ecosystems (NVME) in different parts of the world. This paper attempts to assess the importance of andic soils in mountain ecosystems of Italy. We used the criteria of altitude (> 700 m above sea level), slope (< 12°) and active green biomass (maximum Normalized Difference Vegetation Index (NVDI) value > 0.5) for identifying sites where andic soil processes may occur in the NVME of Italy. We characterized in detail 42 soils in the areas thus identified. According to WRB (2006) the main soils are Andosols, Cambisols, Phaeozems, Umbrisols and Podzols. Despite the taxonomic diversity, the morphological, micromorphological and chemical properties indicate considerable pedological homogeneity in these soils. The most striking features are the large values of Al_o + 0.5Fe_o (as %), which is a standard index for andic soil properties ( USDA, 2006; WRB, 2006 ), but it occurs at the wrong depths for many of our soils to qualify as true Andosol/Andisols and there is little evidence of podzolization. We therefore suggest that (i) andic soils must be recognized more clearly in soil classification, particularly with respect to the depths at which andic properties are developed, and (ii) the importance of andic soils in Italian NVMEs (and possibly elsewhere in the world) has been underestimated. These soils warrant further investigation because of their agricultural potential and ecological importance.     

Shrinkage potential and pore shrinkage capacity of differently developed volcanic ash soils under pastures in southern Chile

The drying process of volcanic ash soils often results in the formation of shrinkage cracks with consequences for their physical properties (i.e., decrease of water retention capacity) and land use management. This study presents the soil water characteristics and shrinkage behaviour (shrinkage phases in terms of void and moisture ratio), the shrinkage potential (COLE index), and the pore shrinkage capacity (PSI) for 5 and 20 cm depth of a Haplic Arenosol (tephric) and two Silandic Andosols under pasture management along a soil gradient from the Andean mountains to the coastal range in southern Chile. The main focus of the presented study is on the effect of soil development in conjunction with the weathering of volcanic ash soils on the shrinkage properties. The water retention and shrinkage curves were continuously determined for undisturbed soil samples (100 cm³) during a drying process under laboratory conditions. In addition, the shrinkage curve data were modelled to distinguish different shrinkage zones. The results suggest that the investigated soil properties vary depending on soil development. The more developed Andosols had higher total porosities (up to 70 cm³ cm^?3) than the less developed Arenosol. The shrinkage behaviour of the Haplic Arenosol showed a wide structural shrinkage phase, whereas the Silandic Andosols revealed a more pronounced proportional shrinkage phase, which is related to the pore size distribution. In addition, wide and narrow coarse pores of the Haplic Arenosol and medium and fine pores of the Silandic Andosols determine the shrinkage potential (COLE) and the pore shrinkage capacity, respectively. The finer‐grained and organic matter‐rich Andosols indicate a higher COLE index (> 0.03–0.09) compared to the Arenosol (≤ 0.03). The pore shrinkage index (PSI) of the total pores (TP) varied significantly (P < 0.05) with values of 0.042–0.149 in 5 cm depth and 0.04–0.091 in 20 cm depth of sites 1–3, respectively.In summary, the shrinkage potential and pore shrinkage capacity are positively correlated to the organic carbon content and decrease with increasing dry bulk density. The study points out a higher risk of soil degradation due to irreversible drying processes for the more clayey and allophane containing Andosols than the Arenosol.     

Late Glacial-Holocene genesis of Andosols from the Seaca-Tãtarca (South Gurghiu Mountains, Romania)

The purpose of the research presented here was to find an answer for the possible origin and mode of deposition of soil parent materials for Andosol formation and to link the soilscape variability to the various soil forming factors since the Last Glaciation. Soil formation was studied along a 20‐km climo‐toposequence in the Miocene Andesitic area of the South Gurghiu Mountains (Romania). Six representative soil profiles were chosen from a larger geopedological study on the western slope of the Seaca‐Tãtarca volcano. Based on the macromorphological, micromorphological and chemical properties it was possible to say that the soil profiles are composed of two major types of soil material: a relict type, with a crystalline clay fraction; and a recent type with an amorphous colloidal fraction. It was found that the present‐day distribution of the Andosols on the Seaca‐Tãtarca volcano must be related to the rejuvenation of the soil parent material by processes of aeolian input of frost‐shattered volcaniclasts and by a glacial reworking. It appears that the extension of the glaciated areas during the Pleistocene could have been larger than concluded from geomorphological studies. General Carpathian glacial features are closely related to the altitudinal distribution of the Carpathian Andosols. At the present climatic optimum, the soils of Seaca‐Tãtarca are influenced by pedogenetic processes of freeze‐thaw, oxido‐reduction, strong leaching and internal colluviation, strong accumulation of organic matter and considerable biological activity. Those Andosols that are located in special microtopographic positions with stronger water percolation tend to evolve towards Podzols.     

Estimating water retention curves of forest soils from soil texture and bulk density

Forest soils differ significantly from the arable land in their distribution of the soil bulk density and humus content, but the water retention parameters are primarily derived from the data of agricultural soils. Thus, there is a need to relate physical parameters of forest soils with their water retention characteristics and compare them with those of agricultural soils. Using 1850 water retention curves from forest soils, we related the following soil physical parameters to soil texture, bulk density, and C content: air capacity (AC), available water capacity (AWC), and the permanent wilting point (PWP). The ACs of forest soils were significantly higher than those of agricultural soils which were related to the low bulk densities of the forest soils, whereas differences in AWCs were small. Therefore, for a proper evaluation of the water retention curves (WRCs) and the parameters derived from them, further subdivisions of the lowest (< 1.45 g cm^‐3) of the three bulk density classes was undertaken to the wide range of low soil densities in forest soils (giving a total of 5 bulk density classes). In Germany, 31 soil texture classes are used for the estimation of soil physical parameters. Such a detailed classification is not required because of insignificant differences in WRCs for a large number of these classes. Based on cluster analysis of AC, AWC, and PWP parameters, 10 texture collectives were obtained. Using 5 classes of bulk densities, we further calculated the ACs, AWCs, and the PWPs for these 10 classes. Furthermore, “van Genuchten parameters” (θ r, θ s, α, and n) were derived which described the average WRC for each designated class. In a second approach using multiple regression analysis, regression functions for AC, AWC, and PWP and for the van Genuchten parameter were calculated.     

Effects of flooding and redox conditions on solute diffusion in soil

Rates of solute diffusion fundamentally affect the properties of flooded soils, but the effects of flooding on solute diffusion have not previously been studied in detail. Four soils with widely differing chemical and physical properties were packed to a range of bulk densities, flooded for varying times, and the self‐diffusion of chloride through the soils measured. Diffusion impedance factors were derived from the results. In each soil the impedance factor decreased linearly with increase in bulk density, and between soils impedance factors increased with increasing clay content. The impedance factor decreased by up to 20% during the first 3–6 weeks following flooding, but with prolonged flooding it increased to at least its initial value. Concomitantly the cation exchange capacities of the soils increased by between 30 and 100%, there was reductive dissolution of soil iron, probably both structural iron in soil clays and iron oxyhydroxide coatings on clay surfaces, and subsequently there was re‐precipitation of ferrous iron, probably as mixed carbonates and hydroxides. The decreases in diffusion impedance factors were consistent with the increases in cation exchange capacity and changes in soil iron, and the subsequent increases were consistent with re‐crystallization of mixed ferrous–ferric compounds. We conclude that the effects of changes in redox on diffusion impedance will be important in some soils, although they are smaller than the effects of water content per se.     

Influence of Soil Chemical Properties on Adsorption and Oxidation of Phenolic Acids in Soil Suspension

Relationships between abiotic oxidation and adsorption of phenolic acids added to soils and soil chemical properties were investigated by using 32 soil samples and ferulic, vanillic, and p-hydroxybenzoic acids. Soil properties studied were as follows: (as adsorption factors) contents of acid oxalate extractable Al (Alo), Fe (Feo), dithionite-citrate-bicarbonate (DCB) extractable Fe (Fed), total carbon and clay, and (as oxidation factors) level of soil oxidative activity (Cr oxidation) determined by the amount of Cr(VI) converted from Cr(III) added to soils. Soil samples were divided into 3 types based on chemical properties: Andosols A (A horizon of Andosols), Andosols B (B horizon of Andosols and light-colored Andosols), and non-Andosols.

The recovery of all phenolic acids (RPA) was negatively correlated with the total carbon and Feo contents in Andosols A and B, respectively, which suggested adsorption onto soil organic matter in Andosols A and onto Feo in Andosols B. It was considered that almost no oxidation of phenolic acids occurred in Andosols A, because a very small amount of Cr(VI) was obtained. The recovery of ferulic acid (RFA) and vanillic acid (RVA), however, was negatively correlated with Cr oxidation in non-Andosols, suggesting that these phenolic acids were oxidized, while almost all of the p-hydroxybenzoic acid was recovered.

These results were also supported by the comparison between RFA and recovery of dissolved organic carbon (RTOC). RFA was very similar to RTOC in Andosols A and B, which indicated that adsorption occurred, whereas RFA was lower than RTOC in the non-Andosols that showed a high level of Cr oxidation, indicating that oxidation took place. Manganese dissolution which occurred when phenolic acids were added to soils was also examined.     

Effect of soil type on the time-course of changes in sugar beet (Beta vulgaris L.) productivity in Tokachi District,Hokkaido, Japan

Abstract

To clarify the effect of soil type on changes in sugar beet (Beta vulgaris L.) productivity since 1980 in Tokachi District (Hokkaido, Japan), we analyzed yield data from 121 settlements from 1980 to 2002 using maps of parent materials and surface organic matter contents in a geographical information system. The soil types were Brown Lowland soils, Andosols with an alluvial subsoil, Wet Andosols and Andosols. The sugar beet yields were highest in the Andosols and moderate in Andosols with an alluvial subsoil. Yields in Brown Lowland soils in the 1980s were similar to those in Andosols, but decreased below the yields in the Andosols by the 1990s. The yields in Wet Andosols were the lowest in the 1980s, but have been similar to those in Andosols with an alluvial subsoil since 1990. Thus, productivity appears to have varied over time in Brown Lowland soils and Wet Andosols. The correlation coefficients between yields and cumulative daily mean temperature from late April to mid-July since 1990 were highest in the Andosols (r = 0.67), lowest in the Brown Lowland soils (r = 0.50) and intermediate in the other soil types (r = 0.54–0.60). However, the magnitude of the correlation between the yield and the cumulative precipitation since 1990 was lowest in the Andosols (r = –0.22), highest in the Brown Lowland soils (r = –0.58) and intermediate in the other soil types (r = –0.44 to –0.45). These results suggest that the present soil water environment in the Andosols is superior to that in the other soil types.     

Organic matter in volcanic soils in Chile: Chemical and biochemical characterization

Abstract

Determinations were made of total soil organic matter (SOM), stable and labile organic fractions, biomass carbon (C), and chemical composition of several humus‐soil‐fractions in Chilean volcanic soils, Andosols and Ultisols. Their physico‐chemical properties and humification degree at different stages in edaphic evolution were also assessed. In addition, organic matter models were obtained by chemical and biological syntheses and the structures and properties of natural and synthetic humic materials were compared with SOM. Results indicate that Andosols have higher SOM levels than Ultisols, but the fraction distribution in the latter suggests a shift of the more stable fractions to the more labile ones. Moreover, contents of humines, and humic and fulvic acids suggest that Chilean volcanic soil SOM is highly humified. On the other hand, among the SOM labile fractions, carbohydrate and biomass are about 15% of the SOM which are one of the most important fractions in soil fertility.     

Aggregation and organic matter in subarctic Andosols under different grassland management

Quantity and quality of soil organic matter (SOM) affect physical, chemical, and biological soil properties, and are pivotal to productive and healthy grasslands. Thus, we analyzed the distribution of soil aggregates and assessed quality, quantity, and distribution of SOM in two unimproved and improved (two organic and two conventional) grasslands in subarctic Iceland, in Haplic and Histic Andosols. We also evaluated principal physicochemical and biological soil properties, which influence soil aggregation and SOM dynamics. Macroaggregates (>250 µm) in topsoils were most prominent in unimproved (62–77%) and organically (58–69%) managed sites, whereas 20–250 µm aggregates were the most prominent in conventionally managed sites (51–53%). Macroaggregate stability in topsoils, measured as mean weight diameter, was approximately twice as high in organically managed (12–20 mm) compared with the conventionally managed (5–8 mm) sites, possibly due to higher organic inputs (e.g., manure, compost, and cattle urine). In unimproved grasslands and one organic site, macroaggregates contributed between 40% and 70% of soil organic carbon (SOC) and nitrogen to bulk soil, whereas in high SOM concentration sites free particulate organic matter contributed up to 70% of the SOC and nitrogen to bulk soil. Aggregate hierarchy in Haplic Andosols was confirmed by different stabilizing mechanisms of micro- and macroaggregates, however, somewhat diminished by oxides (pyrophosphate-, oxalate-, and dithionite-extractable Fe, Al, and Mn) acting as binding agents for macroaggregates. In Histic Andosols, no aggregate hierarchy was observed. The higher macroaggregate stability in organic farming practice compared with conventional farming is of interest due to the importance of macroaggregates in protecting SOM and soils from erosion, which is a prerequisite for soil functions in grasslands that are envisaged for food production in the future.     

Release and recovery of nitrogen from winter annual cover crops in no‐till corn production

Abstract

Soil bulk density markedly influences hydrolysis of surface‐applied granular urea that is vulnerable to serious ammonia volatilization losses. In order to decrease the ammonia losses by retarding urea hydrolysis, several chemicals have been tested for their soil urease inhibition properties. Phenyl phosphorodiamidate (PPDA) is a potent soil urease inhibitor. Laboratory studies using soil column incubations were conducted to investigate the effect of soil bulk density on inhibition of hydrolysis of surface‐applied urea granules (=20 mg of urea/granule) containing 1% PPDA in unsaturated soils. The increase in soil bulk density (from 0.69 to 1.50 Mg/m³) markedly increased the rate of hydrolysis of surface‐applied urea granules and significantly decreased the apparent urease inhibition by PPDA present in the granules. These results are attributed to the probable spatial separation of urea and PPDA because of the differences in diffusive transports in unsaturated soils caused in part by differences in their solubilities in water.     

Comparing NaOH‐extractable organic matter of acid forest soils that differ in their pedogenic trends: a pyrolysis‐GC/MS study

Soil organic matter (SOM) in Alu‐andic Andosols and Alu‐humic Umbrisols is believed to accumulate because of the protection caused by binding to aluminium (Al). We investigated soils that differed in the abundance of organo‐Al complexes to determine the effect of such binding on SOM chemistry. For this, the surface horizons of three types of acid soils in the Basque Country (northern Spain) under forest stands were studied: (i) Alu‐andic Andosols (AND soils) on basalts and trachytes, (ii) Umbrisols or so‐called ‘aluminic’(ALU) soils also on basalts and trachytes and (iii) soils with a podzolizing trend (POD), on quartzites. Values of Al extractable with sodium pyrophosphate (Al_p) in the surface horizons of these soils ranged between 8.5 and 13.1, 1.9 and 9.3, and 0.8 and 3.7 g kg^?1 dry weight, for the AND, ALU and POD soils respectively. For POD and ALU soils, surface horizons were sampled at two depths, 0–5 and 5–20 cm, whereas the AND soils were sampled at different depths down to the B horizon. NaOH‐extractable SOM from three AND soils, 12 ALU soils and 12 POD soils was studied by pyrolysis‐gas chromatography/mass spectrometry. The POD soils had the largest loads of plant‐derived markers (lignin, long‐chain alkanes and alkenes, methyl ketones, fatty acids); SOM of the AND soils had the smallest amounts of plant‐derived SOM and the largest amounts of microbial products (microbial sugars and N‐compounds) of the soils studied. ALU soils had an intermediate pattern, as expected. The results indicate that the SOM of Alu‐andic Andosols, developed from basalt and trachyte rocks, is essentially dissimilar to that of soils derived from quartz‐rich parent material, under the same climate conditions and similar forest stands. The dominance of secondary (microbial‐derived) SOM in Alu‐andic Andosols, also observed in previous research on Sil‐andic Andosols (these are dominated by short‐range ordered Si compounds in contrast to the dominance of organo‐Al complexes in Alu‐andic Andosols), reveals the small contribution of primary (plant‐derived) material to SOM in soils with andic properties.     

Nitrogen immobilization/remineralization in legume‐amended soils as influenced by texture and compaction

Abstract

The role of intrinsic soil properties and management induced changes in bulk density on legume shoot biomass‐nitrogen (N) turnover to soil mineral N [nitrate (NO₃) plus ammonium (NH₄)], SMN, through soil microorganisms is poorly understood. In this study, the influence of intrinsic soil properties and changes in bulk density in soils amended with red clover (Trifolium pratense L.) on N immobilization/remineralization was investigated. Time in incubation, soil type, bulk density, and legume amendment had significant influence on the amounts of microbial biomass carbon (C) (MBC), N (MBN), and the SMN measured during incubation. During the first 32 days in incubation, MBC and MBN in the legume‐amended soils were higher than the control whereas an opposite trend existed for SMN. The SMN measured at the end of incubation, i.e., 70 days after incubation, was significantly higher than the unamended control. The ratio of SMN to MBN (SMN:MBN) was < 1.0, in general, during the first 32 days in incubation in legume amended soils, indicating N immobilization in microbial biomass during this period. Forty‐two days after incubation, the SMN:MBN ratios in the legume amended soils were >1.0, indicating remineralization of the immobilized N, derived, at least partially, from the legume. In the unamended control, these ratios were > 1.0 throughout the incubation. Over time, 63% to 76% of the variability in N‐immobilization/remineralization (SMN:MBN) was accounted for clay content, water (WFP) and air (AFP) filled porosities, volume fraction of pores (VFP) <1.5 μm, total N, C to N ratios in soils, bulk density, and legume amendment. The results indicate the influence of intrinsic soil properties and bulk density on microbially mediated legume N turnover to SMN changed over time.     

Porosity and soil water properties of Caribbean volcanic ash soils

Abstract. Volcanic ash soils are generally recognized as soils with excellent and stable physical properties. Here we characterized the porosity and water properties of volcanic ash Andosols and Nitisols from Guadeloupe in contrasting banana systems: (1) perennial crop without mechanization, (2) mechanized and regularly replanted crop. Desiccation from 1 kPa to 1550 kPa moisture tension leads to significant shrinkage in the Andosol, representing a 50% reduction of the void space. The clayey Nitisol exhibited limited shrinkage. Soil clods from the mechanized plots had a significantly smaller macroporosity than that from perennial plots. The soil hydraulic conductivity was also drastically reduced in the compacted layers of the mechanized plots. However, Nitisols appeared to be less affected than Andosols. Laboratory compression tests showed that both soils were susceptible to compaction at soil moisture close to field capacity. The shrinkage properties of the Andosol were due to microaggregation of non-crystalline components upon drying. The relative stability of the macroporosity in the Nitisol was probably related to the presence of stable microaggregates made of halloysite and iron oxide. Two major processes promote soil structure degradation in the Andosol under mechanized banana cropping, surface desiccation and soil compaction. They are both induced by repeated tillage after clearing.     

Soil compaction and sealing in Al‐Salmi area,western Kuwait

In the deserts of Kuwait in general and in Al‐Salmi area in particular, soil compaction and sealing are the most significant mechanisms of land degradation. In the present study, soil compaction and sealing in the Al‐Salmi area are assessed. The study is based on analysis of satellite images and aerial photographs, besides field measurements and laboratory investigations. Based on this study, a recent map is prepared for the concerned area. It shows three different soil classes. These are highly compacted (8\8 per cent), slightly compacted (1\7 per cent), and almost non‐compacted or natural (89\5 per cent). Soil compaction in Al‐Salmi area causes adverse changes in soil physical properties, e.g. infiltration rate, bulk density and soil strength. The infiltration capacity of the compacted soils has decreased by 18\46 to 91\96 per cent in comparison with non‐compacted soils. The bulk density for the compacted soil varies between 1\6 and 1\7 g cm⁻³, whereas it varies between 1\2 and 1\35 g cm⁻³ in the non‐compacted soils, that is an increased of 29\97 per cent. In some sites, the physical properties show small or no difference between compacted and natural soils due to the effect of soil sealing (crustation). Copyright © 2000 John Wiley & Sons, Ltd.     

Visual structure assessment and mechanical soil properties of re‐cultivated soils made up of loess

Re‐cultivated soils (previously piled soils used as the final surface cover in renovation of open cast mine sites) are particularly susceptible to compaction, which is why a simple estimate of mechanical strength is necessary for land management. In this study, therefore, precompression stress (?6 kPa matric potential) was determined for a total of 20 soil layers from 9 repeatedly cultivated areas of arable land in North Rhine–Westphalia (Germany), along with the aggregate density/dry bulk density ratio (as a measure of density heterogeneity) and air capacity (as a soil ecological parameter). These results are contrasted with the determination of packing density. Packing density (PD) is an integrated parameter that combines various properties (aggregate size, cohesion of the soil structure, root distribution, biogenic macropores and aggregate arrangement) and is assessed visually in the field. Packing density levels range between 1 (very loose soil) and 5 (very highly compacted). There is a strongly negative relationship between packing density and both the aggregate density/dry bulk density ratio and air capacity. Conversely, mechanical precompression stress increases with packing density. Ranges of the individual parameters can be assigned to each of the packing density levels. Packing density level 3 represents an optimization with regard to mechanical soil stability whilst maintaining minimum air capacity requirements (5–8 Vol.‐%).     

梅江盆地叶塘组紫色岩上发育土壤的物理性质研究

采用野外调查、取样和室内实验分析相结合的方法,研究了梅江盆地白垩系上统叶塘组（Kyt^2）紫色岩上土壤物理性质特征扣差异,结果表明：叶塘组紫色岩母质发育的土壤粘粒含量低而砂粒含量高,具有容重较大,比重相对偏小,孔隙度不高,自然含水量偏低的特点。从丘顶、丘腰到丘脚,土层逐渐增厚,土壤粘粒含量逐渐增加,砂粒含量逐渐减少,容重递增而比重减小。孔隙度表现出丘顶〉丘腰〉丘脚的趋势,含水量则表现出丘顶〈丘腰〈丘脚的趋势。针对情况,提出相应建议以维护紫色土利用的可持续发展。     

Radiocesium transfer from Andosols to brown rice in the northern and northwest areas of Tochigi Prefecture,in the first 3 years following the 2011 Fukushima Daiichi nuclear power plant accident

ABSTRACT

Following the Fukushima Daiichi Nuclear Power Plant accident of 2011, the potential for radiocesium transfer from contaminated soils, such as Andosols, to agricultural crops became a significant concern. Andosols account for up to 70％ of paddy soils in the northern and northwest areas of Tochigi Prefecture, where the radiocesium concentration is 1000 Bq kg^?1 or greater in the soil of some fields. The present study was carried out in order to determine the phytoavailability of radiocesium in Andosols by comparing it with that of gray lowland soils in the first 3 years following the accident. The transfer factor (TF) tended to be higher in Andosols than in gray lowland soils, leading to higher radiocesium concentrations in brown rice grown in Andosols. The exchangeable potassium (Ex-K₂O) in Andosols was highly and negatively correlated with TF, followed by clay. The Ex-K₂O value was positively correlated with the clay/total carbon (T-C) value, suggesting that a high T–C ratio could weaken K₂O adsorption on clay mineral sites; hence, the low clay/T-C values can partially explain the relatively large TF values of Andosols. Samples with Ex-K₂O contents less than 200 mg kg^?1 and with low clay/T-C values showed striking decreases in TF values from 2011 to 2012. However, the decrease from 2012 to 2013 was quite small; radiocesium in these samples was potentially available for rice uptake for a long time, likely due to the reversible adsorption and fixation characteristics of allophane. Most gray lowland soil samples showed very low TF values over the 3 years of the study, except for those with TF values greater than 0.1 due to low Ex-K₂O and clay contents; the geometric mean (GM) value of TF was below 0.01 in 2012. The extraction of exchangeable radiocesium (Ex-Cs) with a 1 mol L^?1 ammonium acetate solution may not be an appropriate method for explaining the variability in radiocesium TF in Andosols. This is because the Ex-Cs value was significantly correlated with Ex-K₂O in Andosols, but not in gray lowland soils, indicating that Ex-K₂O explained this variability in relation to Ex-Cs.     

Neutron radiography and tomography of water distribution in the root zone

Water uptake by roots and resulting water redistribution along the soil profile depend on soil hydraulic properties and root distribution, as well as on the physical, chemical, and biological soil–plant interactions that occur in the root zone. The hydraulic properties of the soil in the root zone are difficult to investigate in situ at the needed high spatial resolution, and they still present important open questions. For instance, is there more or less water at the root–soil interface compared to the bulk soil? Neutron radiography (2‐D) and tomography (3‐D) are efficient methods to answer such questions, providing the possibility to image simultaneously water distributions and root structure in situ at high spatial resolution. We planted a lupin and a maize in rectangular boxes filled with sandy soils. The plants were grown for 3 weeks at controlled conditions. Infiltrated water and subsequent water redistribution were imaged for 5 d at regular intervals by means of neutron radiography and tomography. Soil water‐content distributions were quantified from the radiographs after correcting for neutron scattering. The radiographs showed that the water content in the root zone was higher than in the bulk soil both during and after infiltration. Similarly, the tomograms showed localized regions of high water content around some locations of the roots, in particular near the tips of the lupin. Local regions of water depletion, which are expected as a consequence of water uptake, were visible along the main root where laterals branched. These results reflect the complexity of soil–plant–water relations, showing the different properties of bulk soil and root zone, as well as the varying moisture gradients along the root system.