Mineralogical and geo-chemical characterization of a diapiric formation in the North of Spain

We have selected seven profiles located in a diapiric formation in the North of Spain. The profiles have been analyzed for the mineralogy and the chemical composition of original materials, soils developed above them and clay fractions. Three soils formed on basic rock of volcanic origin (ophite) and rich in alterable minerals, three others formed on clay marl and one soil formed on gypsiferous marl. Plagioclases, pyroxenes, vermiculites, and biotites are the main minerals found in the soil samples and ophitic rocks. Biotite, smectite, chlorite and interstratified chlorite–vermiculite make up the predominant mineralogical association in the clay fraction of the soils. Calcite, biotite and on top of all chlorite are the main minerals in the marls and the soils developed on them, with gypsum predominant in the gypsiferous marl. The mineralogy of its clay fraction is comprised mainly of chlorite and biotite. The variations in content of Al₂O₃, TiO₂ and Na₂O in the ophites are considered to be associated with the differences in the evolution of the pyroxenes. The variability of the chemical composition of the Keuper sediments and the soils is attributed more to the chaotic disposition of the Triassic materials in the formation of the diapir than to intense chemical weathering. The low concentrations of silica, iron, and aluminum extractable with ammonium oxalate indicate the low proportion of non-crystalline products. Fundamentally, it is the semiarid conditions in the study zone, together with the processes of extrusion and hydrothermal activity affecting the formation of the diapir, that are responsible for the genesis of the minerals.     

Mineralogy and heavy metal contents of soils and stream sediments in a rural region of Western Germany

This paper presents the results of a study of clay mineralogy and Pb, Zn, Cu, Rb, Sr, Y and Zr analyses of soils and stream sediments of the Schwarzach watershed, a drainage system located in a secluded rural region of eastern Bavaria, far removed from major industrial installations.Clay fractions of soils and stream sediments differ significantly in their mineralogy. The soils average 50% secondary chlorite and 40% illite, whereas recent stream sediments average 20% chlorite and 70% illite. These assemblages are possibly interconvertible under the influence, or on withdrawal, of Schwarzach water. Proportions of clay minerals in fossil stream sediments average approximately 30% chlorite, 50% illite, and 20% kaolinite with up to 10% of 10–14 Å interstratified minerals.Surface soil layers have been enriched in Pb, as have recent stream sediments. The latter have also been enriched in Zn and Cu. The increased amounts of Pb plus its close association with organic C indicate atmospheric deposition of Pb and incipient eutrophication of the Schwarzach River.     

CLAY MINERALS IN SOILS DERIVED FROM LOWER OLD RED SANDSTONE TILL: EFFECTS OF INHERITANCE AND PEDOGENESIS

The clay mineralogy of thirty-two profiles located mainly in the Vale of Strathmore and developed on glacial till derived from Lower Red Sandstone sediments and lavas has been investigated by X-ray diffraction. The soils were selected so that the parent material was related predominantly to one of the rock types common in the Lower Old Red Sandstone succession—namely, marl, sandstone, lava, or conglomerate. Comparison of the < 1.4μm fractions separated from fresh rock samples with those separated from the C horizons of the soils clearly established the dominant influence of parent rock on the soil-clay mineralogy. The clay minerals inherited by the soil often include unusual trioctahedral expansible minerals such as saponite, interstratified vermiculite-chlorite, and smectite-vermiculite, as well as more common types like mica, montmorillonite, and chlorite. Kaolinite is also found but it is not certain that it is only of inherited origin. Weathering of the clays during soil formation brings about complete degradation of the expansible trioctahedral minerals, a process usually well advanced in the B or even at the top of the C horizon, and vermiculitization of mica. The latter process occurs mainly in the A horizon, with concomitant precipitation of interlayer aquohydroxy-aluminium ions thereby forming a vermiculite-chlorite intergrade. Chlorite and kaolinite appear to be little affected by weathering. The weathering transformations are most pronounced in freely drained acid soils (pH < s) and are at a minimum in poorly drained soils and where the pH remains above 6. The susceptibility to weathering of the trioctahedral expansible minerals results in relatively high values for exchangeable magnesium at the base of the profile.     

Unterschiede von Toneigenschaften in Tonstein der fränkischen Lias- und Doggerlandschaften und ihren Böden

Distinctions of Clay Properties in Claystone of the Franconian Lias-and Doggerlandscape and Their Soils Pelosols and Pseudogleys derived from the sediments of the Amaltheen Clay (lias δ), Posidonia Shale (lias δ) and Opalinus Clay (dogger æ) formations in the forelands of the Alb Mountains in Franconia were separated using 16 properties (seven textural and nine chemical properties, the latter of which indicate clay specific properties). Multivariate discriminant analysis was able to distinguish sediments from sediments, sediments from soils and soils from soils. Eight properties were important for discriminating the samples into several groups. Properties with the greatest discriminating quality were the effective buffering capacity for K (BCKe in mval/100 g soil and 100 g clay/M^1/2), the K-fixation (mg K/100 g soil and clay), and the labile K (mval K/100 g soil). The mobile K (ARo in M^1/2) was also an important property. The Pseudogleys were most significantly separated from the Amaltheen Clay and Opalinus Clay sediments. Furthermore, the Pelosols could be significantly separated from Amaltheen Clay and Opalinus Clay on one side and Posidonia Shale on the other. The statistically significant increase of the BCKe and the decrease of ARo as well as some X-ray diagrams suggest that in Pseudogleys derived from Amaltheen Clay and Opalinus Clay and in Pelosols derived from Posidonia Shale expandable forms of 2 : 1 minerals were formed from 10 A-minerals.     

The red soils, their origin, properties, use and management in Greece

Red soils in Greece are distributed throughout the country, but they occur more frequently in the southern provinces and constitute important soil resources supporting several land utilization types. They can be grouped into two categories: the autochthonous and the allochthonous. The former soils are found on hard limestone and on basic igneous rocks in sloping mountainous or hilly landscapes. Moreover, they can be found on mica schists and gneisses in locations adjacent to marble or calcareous mica schists.Allochthonous red soils are wide-spread on late Tertiary and Pleistocene surfaces in the lowlands. Many of these deep deposits have red strata, a few decimeters to several meters thick, or red-colored and fine-textured layers interbedded with light colored deposits of marl, or conglomerates and also with thick strata enriched with calcareous concretions. They are distributed in the thermo- and meso-mediterranean bioclimatic zones. These sites have a common feature, the gently sloping terrain that ensures efficient drainage.There are some differences in chemical and physical properties and in the clay mineralogy of the two groups of Greek red soils. Palygorskite is present in some soils developed on basic rocks; the clay minerals of the allochthonous soils on Pleistocene and late Pliocene seems to be mixed with micas in significant amounts.Soil forming factors required for the formation of red soils are: (a) parent material containing iron-bearing minerals, and rich in bases, (b) slope gradients and/or water permeabilities of the bed-rock securing excessive drainage and (c) vegetation cover that does not produce high amounts of, and deeply distributed organic matter.The allochthonous red soils have likely inherited their color from their parent materials that were transported from the originally formed residual soils on hard limestone. The soils retain the red color in the thermo-mediterranean zone only on sloping terrains. The soils on these landscapes are frequently stratified.The Greek red soils belong to the great groups of: Rhodoxeralfs, Palexeralfs, Xerochrepts, Orthents. Large portions of the allochthonous soils have been desertified or have been severely degraded and their extensive exploitation is not recommended.Soil management practices applied in the allochthonous soils include erosion control, preservation of organic matter, minimum tillage, split application of nitrogen using non-acidifying fertilizers, irrigation, soil water conservation and sheltered agriculture.     

Composition of clay minerals and their pedogenetic and taxonomic implications for Stagnic Anthrosols derived from different parent materials in Hunan Province,China

Purpose

The aims of this study were to investigate the composition of clay minerals in soils derived from different parent materials and to elucidate how parent materials and pedogenic environment affect the distribution of clay minerals and reveal the implications for pedogenetics and taxonomy in Stagnic Anthrosols.

Materials and methods

Clay mineralogy and physicochemical properties of the Hydragric horizon of Stagnic Anthrosols derived from granite (GR), plate shale (PS), quaternary red clays (QRC), limestone (LS), purple sandy shale (PSS) and fluvial-lacustrine deposit (FLD) located in Hunan Province of China were analysed to explore the relationships between the conditions influencing the formation of the soil and the composition of clay minerals.

Results and discussion

Results indicated that the composition of clay minerals is closely related to both parent material and type of Stagnic Anthrosols: the soils derived from GR, PS and QRC, which are mostly classified as Fe-accumulic-Stagnic Anthrosols, are dominantly 1:1 type kaolinite and vermiculite and illite/vermiculite mixed layer minerals of widespread distribution. However, soils derived from LS, PSS and FLD were mainly classified as Hapli-Stagnic Anthrosols and are mainly composed of 2:1 type illite/smectite mixed layer minerals, where chlorite is commonly found. Illite is widely distributed and its content varies the least among different parent materials. An extremely significant relationship between pH and kaolinite, chlorite and mixed layer minerals was noted, and the two kinds of mixed layer minerals showed highly significant negative correlation.

Conclusions

This study revealed that the types and quantities of clay minerals in the soil are closely related to the types of parent material. This reflected better direction and degree of development in Stagnic Anthrosols, which is related to the physicochemical properties of parent material and can be used as one of the bases for the classification of soil groups and subgroups within the soil family for Stagnic Anthrosols in Chinese Soil Taxonomy.

     

Soils in the semi-arid area of the El Melah Lagoon (NE Tunisia) — Variability associated with a closing evolution

Soils of the semi-arid area of the El Melah coastal lagoon (NE Tunisia), with a closing evolution dynamic, were studied aiming: (1) the chemical and mineralogical characterization of surface and subsurface layers of soil profiles from locations previously submerged and of soils developed on dunes; (2) to evaluate the dependence on the environment conditions of the geochemical patterns of the soils; and (3) to determine chemical and mineralogical variations with the emersion of the sediments resulting from the decrease in the extent of the area permanently covered by water in the lagoon. The compositional results obtained showed significant differences depending on the environment (littoral plain, old dunes and sandy spit), but soils of the different environmental zones studied do not appear to be significantly polluted as far as trace elements are concerned. Among the elements studied, high element/Sc ratios and variations were found for As, Sb and Zn. Antimony is more concentrated in coarser samples suggesting its adsorption in Fe or Mn oxides coating quartz grain surfaces. Arsenic and zinc may be incorporated into the carbonates structure, as well as adsorbed on, or coprecipitated with, iron oxides. Zinc may also be significantly incorporated in clay minerals. Iron was found to be more oxidized in the cultivated soil from the old dune strand; and more reduced in the sandy spit where ankerite occurs suggesting the reduction of Fe³⁺ in oxide/hydroxides by microorganisms and incorporation of Fe²⁺ in carbonates. REE patterns, particularly the HREE/LREE are correlated with carbonates, indicating preferential incorporation of the HREE in carbonates, and of the LREE in clay minerals/iron oxides. High Ga contents were found in soils and sediments rich in clay minerals/Al, suggesting its incorporation in clay minerals structure. Therefore, Ga may be used as an indicator of the clay minerals proportion in sediments and soils. Carbonates, sulphates, besides Fe and/or Mn oxides and clay minerals, appear to play an important role on the trace elements distribution.     

Studies on genesis and classification of soils in warm-temperate region of southwest Japan

In the previous paper (1), it was shown that the soil distribution pattern on Pleistocene terraces and hilly areas in the vicinity of Lake Ramana in Tokai region along the Pacific Coast of Southwest Japan has a close correlation to the cyclic development of topography caused by glacio-eustatic movement of sea level during Pleistocene. And it was inferred that in the area Red-Yellow soils occur as relict or buried soils on the older ground surfaces of the higher terraces and foothills which are considered to have been formed before Shimosueyoshi transgression (Riss-Würm interglacial), whereas YellowBrown (Forest) soils develop on the younger ground surfaces of the middle and the lower terraces or upper hillslopes which are considered to have begun to develop after the transgression.     

Mineralogy and nutrient desorption of suspended sediments during a storm event

Purpose

This study investigated desorption of potassium (K) and phosphorus (P) from soil and river suspended sediments sampled during a storm event in a Brazilian watershed traditionally used for tobacco plantations.

Material and methods

Suspended sediment samples were collected automatically at the outlet of the watershed and were grouped into three phases: beginning (phase a), middle (phase b) and final stages (phase c) of the storm event. Granulometric and mineralogical characterisation of soils (0 to 0.20 m depth) and suspended sediments was determined, and K and P extractions were performed using a cation and anion exchange resin (CAER) membrane. A kinetic modelling approach was used to estimate the amount of K and P desorbed.

Results and discussion

Clay-sized (<2 μm) content of the soils were all <21 %. Kaolinite, smectite (partially with hydroxy-Al interlayer) and a small amount of illite were found in the clay fraction of the different soils. The clay-sized fractions in sediments of phases a, b and c of the storm event were 49, 52 and 72 %, respectively. Smectite (>90 %) and kaolinite (<10 %) were the dominant clay minerals in the suspended sediments. The values of labile P and potentially available P of suspended sediments were higher than those for soils. In sediments, the highest values of labile P (325 mg kg^?1) and labile K (4,458 mg kg^?1) were found in phase c and in phase a, respectively.

Conclusions

Particle size distribution and clay mineralogy of soils differed from those of suspended sediments collected during the storm event. By comparison with the watershed soils, suspended sediments collected during the storm event were enriched in fine particles composed mainly of smectite, and this may explain their P and K desorption behaviour. This suggests particle size and clay species selectivity processes during the transfer of sediment particles from soils to aquatic systems. The amounts of P and K desorbed from the suspended sediments in the three phases of the storm event were much larger than those desorbed from soils. This indicates that rainfall promoted the transfer of these nutrients to the watercourses.     

Tonmineral- und K-Ca-Austauscheigenschaften von Oberböden des Nährstoffpotentialversuches Hallertau

Clay mineralogy and K-Ca-exchange properties of surface soils from the nutrient potential trial Hallertau (Bavaria) In soils of four locations of the Hallertau nutrient potential trial, with a soil texture consisting of sand, silty sand, silty loam and sandy clayey loam, clay mineral properties were measured with the standardized glycerol expansion method and with n-alkylammonium (Rn_c-NH₃⁺-clay). The expandable minerals of the sandy soils consist exclusively of smectites s.s., (s.s. = sensu stricto) with 0.42 to 0.28 charge equivalents per formula unit (p.f.u.). The expandable minerals of the loams are an assemblage of smectites s.s. and vermiculites. The total layer charge of the smectites s.s. extend from 0.54 to 0.28 charge eq. p.f.u. The fine clay fractions (< 0.1 μm) do not contain vermiculites. The layer charge density of vermiculites with homogeneous charge in the coarse fractions varies between 0.60 and 0.95 charge eq. p.f.u. The immediate K-Ca-exchange was extended with the values of the continued K exchange versus Ca at low K intensity. The Q/I isotherms of sandy soils have a more pronounced curvature than the isotherms of the loams; in all cases, however, the exchange curves have a continuous form. This phenomen is discussed in terms of the clay mineralogy of the soils. After 8 years without K fertilizing, samples gave values between 168 and 497 kg smectite-K/ha for the surface soils. The constant rates of K-desorption vary between 12.8 and 28.7 kg K/ha (surface soil). The rates are better differentiated between unfertilized and fertilized soils for the loams than for the sandy soils. The constant rates of K release were found to be controlled at an AR-level between 1.6 · 10^?4 M^1/2 (unfertilized sandy soil) and 5.2 · 10^?4 M^1/2 (fertilized sandy clayey loam soil).     

Comparison of the ammonium acetate,Mehlich 3, and sodium tetraphenylboron as extractants to evaluate crop available potassium

ABSTRACT

The 1 M ammonium acetate (NH₄OAc) (AA) is the most widely used method for soil-test potassium (K), but other methods have been also suggested to estimate crop available K. The accuracy of these extractants may be influenced by soil texture and clay mineralogy. This study evaluated the relationships among AA, Mehlich-3 (M3), and sodium tetraphenylboron (TPhB) methods using soils differing in texture and clay minerals from the agricultural area of Uruguay. The M3 and AA extractable K concentrations were highly correlated (R² > 0.97) across soils, although AA extracted slightly higher amount of K than M3. The TPhB method extracted more K than AA and M3, indicating that extracted K from different pools. The slopes of the relationships between TPhB and AA or M3 varied among soils being higher in fine-textured and illitic soils than in coarse soils. These results would be useful for evaluating the feasibility of incorporating M3 into a test program using the existing calibrations of the AA method. In addition, TPhB could be considered a complementary tool to improve the interpretations of the extractants to estimate soil-test K along with other characteristics such as the texture and clay mineralogy.     

Forms and profile distribution of potassium in typical soils of the lower Benue Valley of Nigeria

Abstract

Six profiles, derived from Precambrian Basement Complex rocks (mainly gneiss), Cretaceous sediments (mainly shale and sandstone), and Quaternary alluvium, and which are typical of the major agricultural soils in the Lower Benue Valley (Nigeria) were studied with the objective to determine their overall potassium (K) reserves and any relationship between these and other soil properties including their parent materials. Total K in the soils varies from 0.13–27.1 g kg^‐1 with average 6.64 g kg‐¹. This correlates positively with the clay, and negatively with the sand contents of the soils and is also influenced by their parent materials. The order of abundance according to parent material is: alluvium‐ > Basement Complex (gneiss)‐ ≈ shale‐ > sandstone‐derived soils. The concentrations of readily available K (RAK) in the soils are quite low, accounting for only between 0.30 and 7.8% of the total K in the soils and less than 4.0% of their exchange capacities. Based on critical limits established for many Nigerian soils, the soils derived from sandstone are clearly deficient in RAK, while soils developed from gneiss, shale and alluvium parent materials have moderate to sufficient levels for a wide range of crops. Non‐exchangeable or moderately available K (MAK) in the soils is also relatively low (0.020–8.59 mmol_c kg^‐1); while the sandstone‐derived soils have the least MAK, the alluvial soils have the most levels. However, the potassium supplying power (KSP) of the soils may be considered to be generally high. Although this bears no particular relationship to soil parent materials, the sandstone‐derived soils have the lowest KSP. The bulk of the total K reserves in the soils (55–88%) exists as difficultly available or structural K (DAK). The alluvial soils first, then the gneiss‐ and shale‐derived soils next have the highest contents of DAK, while the highly weathered sandstone soils have the lowest. Simple correlation analysis shows that, irrespective of parent material and K form, clay content and CEC are the most important soil properties influencing the overall K supplying status of these soils. It is concluded that in major agricultural soils of the Lower Benue Valley of Nigeria K exists mostly in the lattice structures of K‐bearing minerals, with accumulations in the subsurface horizons. Its plant‐available or supplying status is low on sandstone‐derived soils and moderate to sufficient on soils derived from Basement Complex rocks, shales and alluvium.     

Amount and composition of clay-associated soil organic matter in a range of kaolinitic and smectitic soils

In the global carbon cycle, soil organic matter (SOM) is a major source/sink of atmospheric carbon. Clay minerals stabilize part of the SOM through mineral–organic matter binding. Stabilization of organic matter is essential for tropical soils. Since the climatic conditions of the tropics favor decomposition of organic matter, tropical soils would be very poor in organic matter without this stabilization process. This research aims at determining the effect of clay mineralogy on the amount and composition of organic matter that is bound to the mineral surface. We focused on organic matter that is associated with kaolinite and smectite. We characterized kaolinite- and smectite-associated SOM in soils from seven countries, employing ¹³C NMR spectroscopy and Py-GC/MS. The content of carbon in the total clay-size fraction showed no significant difference between kaolinitic and smectitic soils. This suggests that the total amount of organic carbon in the clay-size fraction is independent of the clay mineralogy. We first extracted the clay fraction with NaOH and thereafter with Na₄P₂O₇. About half of the kaolinite-associated SOM was extractable by NaOH. In the smectitic soils, pyrophosphate extracted more organic carbon than did NaOH. The Py-GC/MS and NMR results indicate that kaolinite-associated SOM is enriched in polysaccharide products, while smectite-associated organic matter contains many aromatic compounds. We suggest that different clay minerals use different binding mechanisms to complex SOM. As a result, the composition of clay-associated organic matter would be influenced by the type of clay that is dominantly present in the soil.     

Clay mineralogy,chemical weathering and landscape evolution in Arctic–Alpine Sweden

The purpose of this research was to: (1) characterize the clay mineralogy of soils in and adjacent to Kärkevagge, a recently deglaciated valley in Arctic Sweden, (2) document chemical weathering in a periglacial environment and (3) use the mineralogy to help explain landscape evolution. Soil samples were analyzed from 11 sites that differ in elevation, parent material, drainage, slope and vegetation. Parent materials include residuum, alluvium, colluvium and glaciofluvial material derived from garnet–mica–schist, plus, in one locality, a till of granitic origin. X-ray diffraction (XRD) was used to characterize the clay-size fraction (<2 μm). Muscovite, chlorite and mixed-layered (ML) minerals are the predominant soil minerals identified. ML minerals indicate chemical weathering and also act as tracers used to identify source areas of soil parent materials. High concentrations of ML minerals in the soils on the alpine ridges flanking Kärkevagge indicate in situ chemical weathering. At lower elevations within the valley, their distribution indicates that the ridges contributed sediments early on in the evolution of the landscape, but more recently the source has shifted towards ML-poor supply areas from lower elevations. Soil chemistry also supports this model; the alpine soils are base-poor while the valley soils are base-rich. The higher abundance of ML minerals in the alpine zone indicates either a long period of weathering or a greater period of development. The latter explanation supports the hypothesis that the ridge crests were covered by cold-based ice during the last glaciation; remnants of which still survive at the highest elevations. Cold-based ice preserved a pre-weathered landscape that was the primary source of the ML minerals in the soils in the valley.     

Potassium supply capacity response to K-bearing mineral changes in Chinese purple paddy soil chronosequences

Purpose

Purple paddy soils are important for food production. Their potassium (K) supply capacity affects rice yields through its effect on nutrient availability. We hypothesize that changes in soil mineralogy can influence the K supply capacity and the efficiency of K fertilizer. Designing management practices that optimize crop yield while minimizing environmental impacts is a major challenge in agriculture. For this, it is necessary to understand the evolution of, and interaction of, minerals and different chemical forms of K in the soil system.

Materials and methods

Taking advantage of the long-term paddy cultivation history in China, two purple paddy soil chronosequences, one in Guang’an, Sichuan Province (P sequence) and the other in Longsheng, Guangxi Autonomous Region (PS sequence) in Southwest China, were investigated.

Results and discussion

Depotassification is prevalent in both paddy soil chronosequences, which is consistent with the decrease of illite and K-feldspar in the P sequence and with the decrease of muscovite in the PS sequence. K-bearing primary minerals are the long-term stable source of non-exchangeable K (interlayer K) in both chronosequences. Illite in clay fractions acts as the main sources of non-exchangeable K in the P sequence. In contrast, clay minerals derived from muscovite are the main sources of non-exchangeable K in the PS sequence. Clay mineral authigenesis is an important process in the purple paddy soils rich in K-bearing minerals.

Conclusions

The changes in mineralogy of purple paddy soils do not conform to the usual sequence found in the well-drained natural soils. Artificial submergence promotes the conversion of mineral K (lattice-bound K) to non-exchangeable K and enhances the availability of mineral K. The disintegration of K-bearing primary minerals thus controls the K supply capacity in purple paddy soils.

     

MINERALOGY AND GENESIS OF CLAYS IN RED-BLACK SOIL TOPOSEQUENCES ON BASIC IGNEOUS ROCKS IN KENYA

The clay mineralogy of two red-black soil toposequences on basic igneous rocks in Kenya has been investigated. Besides some illite and amorphous material kaolinites predominate in the slope soils (ultisols) whereas smectites are the main clay minerals in the soils of the depressions (vertisols). The kaolinites are poorly crystalline and have high surface area. According to chemical analysis, IR spectroscopy, and D.T.A. the smectites appear to be a ferriferous member of the montmorillonite-beidellite series having approximately 0·5 Fe³⁺ in octahedral and 0·2 Al per O₁₀(OH)₂ in the tetrahedral position. The profile and slope distribution of kaolinites and smectites led to the conclusion that the smectites are the first weathering product and, depending on hydrological conditions governing the soil solution composition (Si, Mg, pH), either persist (depression) or are decomposed (slope) and followed by kaolinites.     

中国东南部某些水稻土的矿物学

Limited information is available concerning the mineralogy of paddy soils in the southeastern China. Using chemical methods in conjunction with X-ray diffractometry, we studied the mineral composition of three paddy soils: Jinghua (paddy soil on Quaternary red clay), Fuyang (Hapl-percogenic loamy paddy soil), and Shaoxing (gleyic clayey paddy soil). All the soils contained quartz, mica, vermiculite, chlorite and kaolinite, and the distribution of these minerals varied with soil particle size fractions. The clay fraction of the Fuyang and Shaoxing soils also contained smectite. Although X-ray data did not show the presence of smectite in the Jinghua soil, this mineral was identified by the chemical method, suggesting a transitional property of the mineral in the soil. Hydroxy-Al interlayered minerals were also present in the clay fraction. The amount of smectite in the soils was 31.6 (Shaoxing), 16.5 (Fuyang), and 21.4 (Jinghua) g kg^-1; for vermiculite it was 33.3 (Shaoxing), 16.5 (Fuyang), and 8.5 (Jinghua) g kg^-1. Smectite was only found in the clay fraction. In contrast, amounts of vermiculite in soil particle size fractions were 3.0~11.4 (sand), 2.1~6.0 (coarse silt), 4.6~18.9 (medium silt), 0.9~40.0 (fine silt), and 17.0~108 (clay) g kg^-1. The amount of noncrystalline aluminosilicates in the soils in g kg^-1 decreased in the order: Shaoxing (2.4) > Jinghua (1.9) > Fuyang (1.7). This study has provided useful mineralogical information that is fundamental in future development of management strategies of the soils.     

Contributions of incorporated residue and living roots to aggregate-associated and microbial carbon in two soils with different clay mineralogy

We conducted a study to investigate the role of aggregates in the stabilization of residue‐ and root‐derived C in an illitic Mollisol and a kaolinitic Oxisol under the following treatments: (i) incorporated residue, (ii) growing plants, and (iii) both incorporated residue and growing plants. Residue‐C dynamics were followed in soils incubated with ¹³C‐labelled wheat residue with and without unlabelled growing wheat plants. Root‐C was traced by growing wheat plants with and without unlabelled wheat residue in a ¹³CO₂‐labelling chamber. After 46 and 76 incubation days, residue‐ and root‐C were measured in four aggregate size classes and in microbial‐C. Both soils had greater residue‐derived than root‐derived total aggregate‐associated C at day 76, which we attributed to the larger residue‐C than root‐C inputs at the start of the experiment. On an aggregate basis, the ratio of residue‐derived over root‐derived C decreased in most size fractions over time, indicating a greater potential for longer‐term root‐C than residue‐C stabilization by aggregates in both soils. At both sampling days, all aggregates > 53 µm had greater residue‐C concentrations in the illitic soil than in the kaolinitic soil and this difference increased with increasing aggregate size. This suggested a greater affinity of illite clay than kaolinite clay to bind with fresh residue‐derived compounds into larger aggregates and hence a greater importance of aggregates in stabilizing residue‐C in illitic compared with kaolinitic soils. The stabilization of root‐C by aggregates was less affected by clay mineralogy and thus less dependent on the affinity of clay minerals to bind with root‐derived compounds.     

Characteristics and classification of three granite-derived soils in peninsular Thailand

The Phuket, Thung Wa and Huai Pong soils of this study form the Phuket catena and are extensive in Narathiwat province in the southern part of peninsular Thailand where they were studied in the field and sampled. The Phuket soils on the higher-lying positions and the Huai Pong soils on the nearly-level, lower positions, have developed argillic horizons and are Ultisols. The Thung Wa soils, which occur on intermediate positions and receive sediments from upslope, have cambic horizons and are classified as Inceptisols.All soils formed from Late Cretaceous or Early Tertiary granite or from sediments derived frome these granites under a tropical rain forest climate. They contain kaolinite as the predominant clay mineral and are highly leached, with base saturation of less than 35% in their B horizons. Cation exchange capacities are less than 6 mequiv. per 100 g soil and exchange acidity and exchangeable aluminium are high. Field and thin-section studies as well as particle-size analysis indicate considerable clay translocation from A to B horizons in the Phuket and Huai Pong soils and little clay movement in the Thung Wa soils.     

广西水耕人为土黏粒矿物组成及其空间分布特征

黏粒矿物影响着土壤理化性质，可指示成土因素特征和土壤发生发育过程/强度，也是中国土壤系统分类的基层单元土族矿物学类型划分的重要依据。本研究选择了广西不同纬度和成土母质的18个代表性水耕人为土的剖面，应用X射线衍射（XRD）方法分析了其典型水耕氧化还原层（Br层）的黏粒矿物组成及其空间分布特征，并确定了其中“黏质”剖面的土族控制层段矿物学类型。结果表明：（1）供试土壤的黏粒矿物主要包括高岭石、伊利石、三水铝石、1.42 nm过渡矿物、蒙脱石和蛭石等，依次分别出现在100%、88.9%、72.2%、61.1%、44.4%和38.9%的剖面中。（2）黏粒矿物组成在纬度空间分布上具有明显规律性特征。随着纬度降低，土壤黏粒中的高岭石增加，伊利石、蒙脱石、1.42nm过渡矿物逐渐减少；纬度＞23°N区域内，成土母质对黏粒矿物组成影响明显。（3）纬度23°N是黏粒矿物组成和土族矿物学类型分界线，＜23°N区域，黏粒矿物均以高岭石为主，是“黏质”剖面的土族控制层段的主要矿物学类型；＞23°N区域，黏粒矿物组成以高岭石、蒙脱石、伊利石或1.42 nm过渡矿物为主，因成土母质不同而异，“黏质”剖面的土族控制层段矿物学类型包括高岭石混合型、混合型和伊利石型。