用激光衍射法评价有机物和和碳酸盐对土壤团聚的作用

>Aggregation in many soils in semi-arid land is affected by their high carbonate contents.The presence of lithogenic and/or primary carbonates can also inffuence the role of soil organic matter(SOM) in aggregation.The role of carbonates and SOM in aggregation was evaluated by comparing the grain-size distribution in two carbonate-rich soils(15% and 30% carbonates) under conventional tillage after different disaggregating treatments.We also compared the effect of no-tillage and conventional tillage on the role of these two aggregating agents in the soil with 30% of carbonates.Soil samples were treated as four different ways:shaking with water(control),adding hydrochloric acid(HCl) to remove carbonates,adding hydrogen peroxide(H2O2) to remove organic matter,and consecutive removal of carbonates and organic matter(HCl + H2O2),and then analyzed by laser diffraction grain-sizing.The results showed that different contributions of carbonates and SOM to aggregate formation and stability depended not only on their natural proportion,but also on the soil type,as expressed by the major role of carbonates in aggregation in the 15% carbonate-rich soil,with a greater SOC-to-SIC(soil organic C to soil inorganic C) ratio than the 30% carbonate-rich soil.The increased organic matter stocks under no-tillage could moderate the role of carbonates in aggregation in a given soil,which meant that no-tillage could affect the organic and the inorganic C cycles in the soil.In conclusion,the relative role of carbonates and SOM in aggregation could alter the aggregates hierarchy in carbonate-rich soils.     

依据传统土壤数据应用数字土壤制图法对香港山地地区土壤建立土纲信息

Based on legacy soil data from a soil survey conducted recently in the traditional manner in Hong Kong of China, a digital soil mapping method was applied to produce soil order information for mountain areas of Hong Kong. Two modeling methods (decision tree analysis and linear discriminant analysis) were used, and their applications were compared. Much more eflort was put on selecting soil covariates for modeling. First, analysis of variance (ANOVA) was used to test the variance of terrain attributes between soil orders. Then, a stepwise procedure was used to select soil covariates for linear discriminant analysis, and a backward removing procedure was developed to select soil covariates for tree modeling. At the same time, ANOVA results, as well as our knowledge and experience on soil mapping, were also taken into account for selecting soil covariates for tree modeling. Two linear discriminant models and four tree models were established finally, and their prediction performances were validated using a multiple jackknifing approach. Results showed that the discriminant model built on ANOVA results performed best, followed by the discriminant model built by stepwise, the tree model built by the backward removing procedure, the tree model built according to knowledge and experience on soil mapping, and the tree model built automatically. The results highlighted the importance of selecting soil covariates in modeling for soil mapping, and suggested the usefulness of methods used in this study for selecting soil covariates. The best discriminant model was finally selected to map soil orders for this area, and validation results showed that thus produced soil order map had a high accuracy.     

Combined application of a straw layer and flue gas desulphurization gypsum to reduce soil salinity and alkalinity

Burying a straw layer and applying flue gas desulphurization(FGD)gypsum are effective practices to ameliorate soil salinization or alkalization and to increase crop yield;however,little information exists on the effects of such integration in saline-alkali soils.A soil column experiment was conducted to investigate the effects of a straw layer plus FGD gypsum on soil salinity and alkalinity.We placed a straw layer(5 cm thick)at a depth of 30 cm and mixed FGD gypsum into the 0–20 cm soil layer at application rates of 7.5,15.0,22.5,and 30.0 t ha^-1,with no straw layer and FGD gypsum as a control(CK).The soil water content in the 0–30 cm soil layer was significantly higher(>7.8%)in the treated soil profiles after infiltration than in the CK,but decreased after evaporation.The electrical conductivity(EC)of the 10–30 cm soil layer was 230.2%and 104.9%higher in the treated soil profiles than in the CK after infiltration and evaporation,respectively,and increased with increasing rates of FGD gypsum application,with Ca^2+and SO4^2-being the main dissolved salts.Compared to those in the CK,the concentrations of Na^+,Cl^-,and HCO3-decreased in the treated soil profiles at depths above 55 cm,but the other soluble ions increased,after infiltration.A similar trend occurred after evaporation for all soluble ions except for HCO3-.The p H and exchangeable sodium percentage in the treated soil profiles were significantly lower than those in the CK over the entire profile,and decreased with increasing FGD gypsum application rates.Therefore,the incorporation of a straw layer plus FGD gypsum can reduce salinity and alkalinity,but the quantity of FGD gypsum should be controlled in saline-alkali soils.     

由石灰性冲积物发育而来的排水不良和排水良好的土壤中游离氧化物的分布

A study on the distribution of free iron and manganese oxides was conducted in soils developed on calcareous alluvial deposits under subhumid climatic conditions, in Western Greece. Soil samples from two well drained soils and from two poorly drained soils, classified as Alfisols, were collected and used in this study. After certification of soil homogeneity the acid ammonium oxalate and dithionite-citrate-bicaxbonate methods were used to extract free iron and manganese oxides from the samples. Iron oxides extracted by the dithionite-citrate-bicarbonate method (Fed) were significantly higher than the iron oxides extracted by the ammonium oxalate method (Feo), indicating that a considerable fraction is present in crystalline forms, independent of drainage status. A confirmation of free iron oxides and fine clay was detected. The ratios Feo/Fed and (Fed-Feo)/total Fe (Fet) could not be used to distinguish the well drained soils from the poorly drained soils. Manganese movement in a soluble form is independent of the fine clay.     

干湿交替对半干旱地区一些铅盐污染土壤中铅再分配的影响

Mobility and bioavailability of lead (Pb) could be affected considerably by soil physicochemical properties;however,less is known about the effect of Pb levels and aging time.This study was conducted to evaluate the effects of Pb levels and wetting-drying (WD) cycles on distribution and bioavailability of Pb in three semi-arid zone soils treated with different levels of Pb(NO 3) 2.Wetting-drying cycles simulated the actual field irrigation in the semi-arid soils.A soil with a long history of Pb contamination was also taken as a reference soil.The soils were spiked with various levels of Pb and incubated under WD cycles for 160 d.Sequential extractions and batch sorption experiments were performed to assess the fractionation of Pb in the spiked soils.Redistribution index (U ts) and reduced partitioning parameter (I R) were applied to semi-quantify the distribution of Pb in the spiked soils.A small amount of Pb sorbed was desorbed by the soils,indicating a strong and irreversible binding of Pb in the studied soils.Contribution of carbonate-bound (Car) and residual (Res) Pb fractions to the total Pb of the soils was more than 97%.The Car,soluble plus exchangeable (SE),and organic matter-bound (OMB) fractions of Pb were transferred to the Res fraction under the WD cycles.The I R and U ts values were influenced by Pb loading levels and WD;therefore,the Pb lability and/or redistribution pattern could semi-quantitatively be assessed via these parameters.At the end of the experiment,the I R and U ts values for the Pb salt-spiked soils did not show the quasi-equilibrium state.The lability of Pb in the soils decreased with increasing incubation time and showed a strong dependence on Pb levels and soil chemical composition.WD cycles significantly affected the overall lability of Pb in soils through influencing the redistribution of Pb among solid-phase components.     

悬着水位对铝硅酸盐的稳定性及土壤发生的影响

The mineral stability and solute activities of soil solution extracted from selected horizons of seven studied pedons of Alfisols in Kentucky, USA, and the relationship between distribution of iron-manganese concretions and the restrictive layers were investigated. The results showed that the genesis and development of these soils and mineral weathering trends were strongly influenced by the depth of bedrock and the presence of perched water tables at lithic (limestone) interfaces due to the dissolution and buffering effect of limestone bedrock. The extractable Mg/Ca ratio as depth function and soil depth above bedrock could be used as indices of weathering and degree of soil development. Maximum iron-manganese concretion accumulation was found to occur in the horizon overlying clay horizon (>40% clay) with a sharp increase in clay content (>10%), which suggested that zones of Fe-Mn concretion accumulation in soils of the Inner Bluegrass Region appeared to be a sensitive genetic indicator of argillic horizons with restrictive permeability.     

小麦和燕麦两种作物镁吸收和坡缕石转化能力研究

Weathering of clay minerals is a source of nutrients to plants. Palygorskite is a Mg-rich fibrous clay mineral that commonly occurs in the soils and sediments of arid regions. Although many studies have examined the environmental conditions required for the formation and stability of palygorskite, information on the transformation of this mineral in the root zone (or rhizosphere) of agricultural crops is limited. This study explored the possibility of palygorskite transformation in the rhizosphere of wheat and oat and compared the ability of these crops to extract structural Mg from palygorskite. The crops were cultivated in pots consisting of a mixture of sand from Hamadan region, Iran and Florida palygorskite, irrigated with distilled water, and treated with either complete or Mg-free nutrient solutions. After 100 d, Mg uptake by the crops was measured. Clay-sized particles in each pot were also separated from the sand and were analyzed through X-ray diffraction (XRD). The X-ray pattern of the particles was compared with that of the pure palygorskite particles (before cultivation). The results showed that palygorskite could provide sufficient Mg for the growth of wheat in the pots supplied with Mg-free nutrient solution. In spite of the magnesium uptake by both plants from the palygorskite structure, no detectable peaks indicating the transformation of palygorskite were recognized by XRD. A decrease of 1.05 nm in peak intensity was more obvious for the pots containing palygorskite and irrigated with Mg-free nutrient solution than for the pots irrigated with complete nutrient solution. Although the decrease in peak intensity was greater for oat than wheat, indicating greater palygorskite weathering by oat, Mg uptake by oat was low, as evidenced by the deficiency symptoms observed.     

重金属迁移与土壤性质的关系

Cu, Zn, Pb and Hg runoff from yellow limestone soil and purple soils and the relationships between the mobility of the heavy metals and the soil characteristics were studied in laboratory using a rainfall simulator. The results showed that the concentrations of soluble Zn in surface runoff were significantly negatively correlated with the contents of < 0.002 mm particles and CEC of the soils, indicating that Zn was mostly adsorbed by clays in the soils. The contents of Cu and Hg in surface runoff were positively related to their contents in the soils. The amounts of Cu, Zn, Pb and Hg removed by surface runoff were influenced by the amounts of soil and water losses and their contents in the soils, and were closely related to the contents of soil particles 1~0.02 mm in size.     

不同土地利用方式下上壤微生物群落水平生理图谱(CLP)与土壤碳、氮有效性之间的相互关系（英文）

The goal of this work was to assess soil microbial respiration,determined by the assay of community-level physiological profiling in an oxygen-sensitive microplate(O2-CLPP),in response to endogenous C and several individual C substrates in the soils with different organic C contents(as a function of soil type and management practice).We also used the O2-CLPP to determine the respiratory response of these soils to endogenous C and amended C substrates with N addition.A respiratory quotient(RQ) was calculated based on the ratio of the response to endogenous soil C vs.each C-only substrate,and was related to total organic carbon(TOC).For assessing N availability for microbial activity,the effect of N supplementation on soil respiration,expressed as N_(ratio),was calculated based on the response of several substrates to N addition relative to the response without N.Soils clustered in 4 groups after a principal component analysis(PCA),based on TOC and their respiratory responses to substrates and endogenous C.These groups reflected differences among soils in their geographic origin,land use and C content.Calculated RQ values were significantly lower in natural forest soils than in managed soils for most C-only substrates.TOC was negatively correlated with RQ(r = —0.65),indicating that the soils with higher organic matter content increased respiratory efficiency.The N addition in the assay in the absence of C amendment(i.e.,only endogenous soil C present) had no effect on microbial respiration in any soil,indicating that these soils were not intrinsically N-limited,but substrate-dependent variation in N_(ratio) within soil groups was observed.     

城市土壤特征土层的数值分类

Pedogenetic soil horizons are one of the fundamental building blocks of modern soil classification; however, in soils of urban areas which are often strongly disturbed by human activities, horizons are difficult to distinguish but substitutive morphological layers may be identified. To identify the characteristic soil layers in an urban environment, 224 soil layers of 36 in-situ pedons were examined and described in urban and suburban Nanjing, and 27 variables were extracted for multivariate analysis. Three groups and six subdivisions were identified by TwoStep cluster analysis combined with hierarchical cluster analysis based on factor scores. Soil forming factors and soil forming processes could be interpreted from the principal component analysis （PCA） of variables, cluster analysis of soil layers, and discriminant analysis of soil layer groups and their subdivisions. Parent materials, moisture regimes, organic matter accumulation, and especially nutrient accumulation were the main causes of characteristic soil layer formations. The numerical approaches used in this study were useful tools for characteristic soil layer identification of urban soils.     

CHARACTERISTICS OF NUBIAN SANDSTONE-DERIVED SOILS

Nubian sandstone exposures in sub-humid, semi-arid, and arid environments have given rise to red, sandy but in other respects very different soils. Soils have a fairly well developed profile only in the sub-humid zone, including a textural B horizon and are free of soluble salts and carbonates. In the semi-arid and arid zones, profile differentiation is weak or non-existent. Soils are shallow and contain carbonates, and in the arid zone also soluble salts, including gypsum. Kaolinite is the only clay mineral which is common to all the nubian sandstone parent materials. It is the major clay mineral in the sub-humid zone soil. In the semi-arid soils smectite is a second major clay component. In the arid zone both smectite and palygorskite, in minor amounts, accompany kaolinite. Both smectite and palygorskite are probably pedogenic neoformation products. Material of aeolian origin has probably been introduced into the silt and fine sand fractions of both the semi-arid and arid soils. Some contamination of the clay fractions may have also occurred.     

Dispersion and migration of fine particles in two palygorskite‐containing soils of the Jordan Valley

Migration of different mineral particles within columns of soil‐sand mixtures containing 10 or 20 mass % of soil was investigated by establishing differences in the mineral suite between the ”︁bulk clay” and the ”︁mobile fine material” fractions. The ”︁bulk clay” fractions of all soils contained smectite, palygorskite, kaolinite, quartz, feldspar, and calcite. The soils were saturated with sodium by leaching with NaCl solution, and then leached with distilled water. Clay dispersion and particle migration occurred in the columns. Values of SAR (sodium adsorption ratio) of the effluent decreased with time due to carbonate dissolution. At a certain SAR value, the clays apparently formed aggregates, and as a consequence particle migration stopped in the column. In addition to clay‐sized particles (< 2 μm), very‐fine‐silt‐sized particles (2— 5 μm) were able to migrate in the soil‐sand mixtures, too, and to some extent fine‐silt‐sized particles (5—10 μm) as well. Average size of mobile particles decreases with increase of soil content in the soil‐sand mixtures. The mineralogical composition of the ”︁mobile fine material” changed during the experiment. At the beginning of the experiment, the ”︁mobile fine material” was enriched in the non‐phyllosilicates (especially in calcite, and in some cases in quartz, feldspar and dolomite) and contained low concentrations of phyllosilicates (smectite, palygorskite and kaolinite). At the end of the experiment, the proportion of non‐phyllosilicates decreased, and as a consequence, the proportion of phyllosilicates increased. Among the non‐phyllosilicates, calcite was the most mobile mineral. Among the phyllosilicates, palygorskite was preferentially mobilized in topsoil horizons. In subsoil horizons, on the other hand, kaolinite was preferentially mobilized. This difference was explained by the different nature of carbonates in the topsoil and subsoil horizons. Palygorskite is preferentially occluded within the soil carbonates of lacustrine origin over smectite and kaolinite. These carbonates are present mainly in the subsoil horizons. As a consequence, the presence of these carbonates in the subsoil horizons decreases the migration of mainly palygorskite.     

Flow-associated precipitation reactions in saline-sodic soils and their significance

A saline-sodic soil (pH 10.0, ESP 100.0, total soluble salts 10.0 mequiv./100 g) rich in soluble sodium carbonate (7.8 mequiv./100 g) was leached in the laboratory with calcium-containing water. The effect of varying flow velocities and concentration of calcium in the leaching water on the extent of carbonate precipitation was studied by following the composition of leachate in one set of experiments and the redistribution of soluble carbonates in the soil column in another experiment. The results showed that precipitation of soluble carbonates in the soil increased with increasing flow velocity and concentration of calcium in the leaching solution. The results have been discussed in terms of actual flow processes occurring at the wetting front. It is suggested that by controlling the extent of carbonate precipitation, the quantity of amendments containing calcium necessary for the reclamation of sodic soils rich in soluble carbonates can be considerably reduced. The results also suggest that the usual method of determining the gypsum requirement of soils is likely to overestimate the gypsum needs of these soils because a large portion of the soluble carbonates is leached out without reaction with the added gypsum.     

Influences of quaternary climatic changes on processes of soil development on desert loess deposits of the Cima volcanic field, California

Soils formed in loess are evidence of both relict and buried landscapes developed on Pliocene-to-latest Pleistocene basalt flows of the Cima volcanic field in the eastern Mojave Desert, California. The characteristics of these soils change systematically and as functions of the age and surface morphology of the lava flow. Four distinct phases of soil development are recognized: phase 1 - weakly developed soils on flows less than 0.18 M.y. old; phase 2 - strongly developed soils with thick argillic horizons on 0.18 – 0.7 M.y. old flows; phase 3 - strongly developed soils with truncated argillic horizons massively impregnated by carbonate on 0.7 to 1.1 M.y. old flows; and phase 4 - degraded soils with petrocalcic rubble on Pliocene flows. A critical aspect of the development of stage 1 soils is the evolution of a vesicular A horizon which profoundly affects the infiltration characteristics of the loess parent materials. Laboratory studies show that secondary gypsum and possibly other salt accumulation probably occurred during the period of phase 1 soil development. Slight reddening of the interiors of peds from vesicular-A horizons of phase 1 soils and presence of weakly developed B horizons indicates a slight degree of in situ chemical alteration. However, clay and Fe oxide contents of these soils show that these constituents, as well as carbonates and soluble salts, are incorporated as eolian dust. In contrast to phase 1 soils, chemical and mineralogical analysis of argillic horizons of phase 2 soils indicate proportionally greater degrees of in-situ chemical alteration. These data, the abundant clay films, and the strong reddening in the thick argillic horizons suggest that phase 2 and phase 3 soils formed during long periods of time and periodically were subjected to leaching regimes more intense than those that now exist. Flow-age data and soil-stratigraphic evidence also indicate that several major loess-deposition events occurred during the past 1.0 M.y. Loess events are attributed to past changes in climate, such as the Pleistocene-to-Holocene climatic change, that periodically caused regional desiccation of pluvial lakes, reduction of vegetational density, and exposure of loose, unconsolidated fine materials. During times of warmer interglacial climates, precipitation infiltrates to shallower depths than during glacial periods. Extensive, saline playas which developed in the Mojave Desert during the Holocene are a likely source of much of the carbonates and soluble salts that are accumulating at shallow depths both in phase 1 soils and in the formerly noncalcareous, nongypsiferous argillic horizons of phase 2 and 3 soils.     

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.     

Potassium fixation of some calcareous soils after short term extraction with different solutions

This investigation was done to determine the release of potassium (K) from five calcareous soils of southern Iran using 0.025 M CaCl₂, HCl and citric acid during six successive extractions and to study the K fixation capacity of the soils after K release experiment. Mineralogical study indicated that Vertisols and Mollisols were dominated with smectites; while other soils had illite, chlorite, palygorskite and smectite. Results indicated that citric acid extracted more K than CaCl₂ and HCl (137 vs. 111 and 113 mg kg^?1, respectively). The analysis of calcium (Ca), magnesium (Mg) and K concentrations in the solutions suggests that the exchange of K with soluble Ca and Mg (originated from dissolution of carbonates by acidic solutions) is the main mechanism of K release, but citrate is able to dissolve K-bearing minerals and release K in slightly calcareous soils. Soils with more illite released more K. Potassium fixation capacity of soils increased after extractions of soils with different extractants from 324 to 471 mg kg^?1, with no significant difference. It is suggested to apply more K fertilizers in K-depleted calcareous soils and use of different solutions for extracting K from soil minerals may be a temporary and short term solution.     

Reclamation of saline‐sodic soil under a rice–wheat system by horizontal surface flushing

Saline sodic soil with a high content of soluble carbonates is one of the important agricultural soils on the Central Indo‐Gangetic plains and elsewhere. Conventional reclamation procedures using gypsum application followed by vertical leaching (GC) is uneconomic; high ECe and precipitation of applied gypsum, reacting with soluble carbonates, reduce the efficacy of gypsum in these soils. This paper reports results from a project designed to evaluate reclamation by irrigation of the ploughed soil and turning of soil with a power tiller followed by flushing of standing water after 24 h, a second flushing after 7 days and subsequent application of gypsum and vertical leaching (GF2). Average rice and wheat production after GF2 significantly increased (25 and 62%, respectively) over the conventional practice. Compared with conventional treatment, GF2 significantly reduced the ECe and SAR of the soil and improved physical properties such as ζ‐potential, dispersible clay content, water stable aggregates expressed as MWD, and saturated hydraulic conductivity. Split application of gypsum between flushing (GF1/2 and GF2/3) gave similar results to GF2 in terms of soil amelioration and crop production.     

Similarities and differences of the spheroidal microstructure in Vertisols from Turkey and Israel

Vertisols formed on different parent materials from Turkey (Aslanpınarı and Begde soil series) and Israel (Akko soil series) were studied for their microstructure. The Aslanpınarı and Begde soils showed similar spheroidal microstructural development in the ABss horizons, whereas the spheres of Akko differed by being smaller and lacking granostriation. Micromorphometric analyses of the three soils revealed similar pore characteristics within and between the aggregates of the ABss horizons. Presence of the spheroidal microstructural units and increase of palygorskite and vermiculite in the ABss horizon of the Be de soil, which is in contrast with increasing smectite in the Aslanpınarı and Akko soils, links with an increase in the structural stability index and an increase in the hydraulic conductivity.