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Micromorphology of Surface Crusts in the Knersvlakte,South Africa

Journal of Mountain science 2009年第2期6卷 189-196页

作者： Sarah-Jane C.Fox Anthony J.Mills Rosa M.Poch department of soil science Stellenbosch UniversityStellenbosch South Africa department of Environment and soil science University of LleidaRovira Roure 191 Lleida

soils in the Knersvlakte are particularly prone to crusting and have lower inherent infiltrability than other soils across western southern Africa. Micromorphological techniques were used to examine the structure and porosity of soil crusts in the Knersvlakte to ascertain why crusting is so intense in this region. Quantile regression using boundary lines was employed to examine the relationships between infiltrability and soil properties for all samples （n = 67）. This analysis showed that infiltrability is potentially maximal at low water- dispersible ＇clay plus silt＇ content and low silt content （r^2 = 0.72 and 0.64; respectively, n = 67）（Figure 2）. The strength of crusts, pH, EC, clay mineralogy, and water-dispersible clay, silt and ＇clay plus silt＇ content were compared, and a pore analysis using optical microscopy was undertaken on images of six soil thin sections （n = 6）（circular and parallel polarizers）. Pore analysis was further undertaken on five horizontal slices of equal dimensions taken through each soil thin section. The porosity samples with low infiltrability （〈 100 mm·hr^-1, n = 4） had greater crust strength, lower porosity （both total and in the least porous slice） and greater water-dispersible ＇day plus silt＇ and silt content than the porosity samples with high infiltrability （〉 100mm·hr^-1, n = 2）. The porosity samples with low infiltrability showed a trend of lower pH and greater water dispersible clay percentage. Porosity varied within the porosity samples due to the presence of dense clay/silt bands （〈 0.5 mm in width） with relatively few air vesicles. The porosity samples with horizontal slices of low porosity （but large numbers of air vesicles） had low infiltrability, while those without slices of low porosity （and relatively few air vesicles） had high infiltrability. We conclude that the intense crusting and resultant low infiltrability of soils in the Knersvlakte appears to be related to the formation of thin, dense clay/silt bands in the

关键词： Infiltrability optical microscopy porosity air vesicles

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Origin of Sulfur and Mode of Gypsum Formation in Central Iraqi soils

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Journal of Mountain science 2013年第5期10卷 734-742页

作者： Sabar Rahi Jasem ALJEBOORY Ahmad MUHAIMEED MohammadHady FARPOOR KA SALIeM soil science department College of AgricultureUniversity of Baghdad soil science department College of AgricultureShahid Bahonar University of Kerman Ministry of Agriculture

The δ18O and 8D values of gypsum crystallization water together with δ18O and 834S of sulfates were used as reliable techniques to study source of sulfur and mode of gypsum formation in selected central Iraqi soils. Six representative pedons on different geologic units were studied. The slope of 3.9 for δ18O and 8D plot of gypsum crystallization water showed that evaporation was the major process of gypsum deposition in the study area. The mean 834S value of ＋17.58 %0 showed that Cretaceous sea sulfate followed by Tertiary is the source of sulfur in studied soils. The heavier 834S value （＋17.58 %0） of the study area compared to central Iran （＋13.5 %） proved that gypsum in central Iraq soils has been formed in the later stage of evaporation and that Iraqi landforms were cut off from the Tethys seaway after central Iran was evolved.

关键词： Sulfur geochemistry Gypsumcrystallization water Tethys Sea Iraq

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Element Abundances of China's Continental Crust and Its Sedimentary Layer and Upper Continental Crust

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Chinese Journal Of Geochemistry 1995年第1期14卷 26-32页

作者：黎彤 department of geology University of Science and Technology Beijing

China's continental crust (CCC)has an average thickness of 47km,with the uppercontinental crust (CUCC)being 31 km and the sedimentary layer(CSL)5 km in *** CCC,CUCC and CSL measure 12.437×10^17,8.005×10^17 and 1.146×10^17 metric tons in mass,*** mass ratio of the upper continental crust to the lower one is 1.8:*** element abundances were calculated for the CCC,CUCC and CSL respectively in terms of the chemical compositions of 2246 samples of various types and some complementary trace element *** total abundance of 13 major elements accounts for 99.6% of the CCC mass while the other minor elements only account for 0.4%.REE characteristics,the abundance ratios of element pairs and the amounts of ore-forming elements are also discussed in the present paper.

关键词：中国大陆地壳沉积地层沉积物元素成矿元素稀土元素

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Cadmium speciation as influenced by soil water content and zinc and the studies of kinetic modeling in two soils textural classes

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International soil and Water Conservation Research 2020年第3期8卷 286-294页

作者： Farzad Rassaei Mehran Hoodaji Seyed Ali Abtahi department of soil science Isfahan(Khorasgan)BranchIslamic Azad UniversityIsfahanIran department of soil science Shiraz UniversityShirazIran

Background and aims:Since few studies have existed in the literature about the effect of zinc(Zn)on cadmium(Cd)chemical forms in ***,this study has been performed to determine the impact of Zn on cadmium Cd chemical forms in two soil textural classes in Fars province-Iran at two soil water content(SWC)(flooded soil water content(FSWC)and field capacity soil water content(FCSWC))and study the kinetic modeling of *** and materials:Variables were three levels of Cd(0,30 and 60 mg kg-1 of soil as CdSO4·8H2O),three levels of Zn(0,5 and 10 mg kg-1 of soil as Zn-EDTA)three level Incubation times(2,4 and eight weeks),two soil textural classes(clay and sandy clay loam)and two *** randomized completed block design(RCBD)was used for this *** Tessier sequential extraction method was used to determine the Cd concentration in(WsEx),(Fe-MnOx),(Car),(Om)and(Res)chemical ***:In the FSWC,Zn reduced the Cd concentration in Fe-MnOx,Car and Om forms and increased the WsEx but had no significant effect on the Res *** in the Cd chemical forms under the in-fluence of Zn in both soils followed a similar *** the FCSWC,Zn reduced the Cd concentration Car and Om forms and increased the Cd concentration in the Fe-MnOx and WsEx forms while had no sig-nificant effect on Res form in the sandy clay loam *** the clay soil adding Zn reduced the Cd con-centration in Car and Om fractions and increased the Fe-MnOx and Res forms while has no significant effect on WsEx *** competitive transport and adsorption Interactions between these two ions caused the changing in the Cd concentration in its chemical *** reduces the Cd concentration in the forms which are easily released into the soil solution from where they can be absorbed by *** power function kinetic mode is the best fitted model which can describe the Cd adsorption in our soil *** clay and organic compounds control the Cd adsorption in *** higher rate of C

关键词： Cadmium Chemical forms Field capacity Flooding condition Kinetic model Sequential technique soil water content Zinc

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Modeling Runoff from Semi-Arid Agricultural Lands in Northwest Iran

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Pedosphere 2014年第5期24卷 595-604页

作者： A.R.VAEZI department of soil science Agriculture Faculty University of Zanjan

Transformation of rainfall into runoff over an area is a very complex process which exhibits both temporal and spatial variability;runoff in a defined area can be affected by factors such as topography, vegetation, rainfall characteristics and soil properties. This study was conducted to develop an empirical model using the rainfall characteristics and soil properties for predicting runoff from dry-farming lands in a semi-arid agricultural area in Hashtroud, Northwest Iran. Runoff plots(1.83 m × 22.1 m) in triplicate were installed in thirty-six sloped dry-farming lands in the study area. Runoff under natural rainfalls was measured in each plot during a2-year period. The results showed that runoff for 41 runoff-producing rainstorm events with duration longer than 30 min was largely associated with a rainfall index obtained by multiplying the positive square root of rainfall depth(h0.5) by the logarithm of the maximum 30-minute intensity(LogI30)(R2= 0.81). Runoff significantly varied among the plots(P soil properties(R2= 0.74), i.e., soil permeability(Per) and aggregate stability(AS). A multiple linear regression model was developed between runoff and the rainfall index(h0.5logI30) and the effective soil properties(AS and Per). Evaluation of the model using 34 runoff-producing rainstorm events that occurred during the next two years resulted in high values of the efficiency coefficient and R2(0.88 and 0.91, respectively), which revealed that the model developed in this study could be used in predicting runoff from the dry-farming lands in the semi-arid regions.

关键词： aggregate stability dry-farming lands natural rainfall rainfall depth rainfall index rainfall intensity soil permeability

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Kinetics of Ligand-Controlled Release of Zinc in Acid Sulfate Paddy soils

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Pedosphere 2019年第2期29卷 216-223页

作者： Worachart WISAWAPIPAT Aksarapak PONGPOM department of soil science Faculty of Agriculture Kasetsart University

The elevated solubility of zinc(Zn) in acid sulfate paddy soils can limit rice production and pose a risk of environmental ***, little attention has been paid to the ligand-controlled release of Zn in these soils. Here we quantified the rate of ligandcontrolled Zn release in Thai acid sulfate paddy soils, using ethylenediaminetetraacetic acid as the extractant. Sequential extractions were performed to obtain quantitative information on Zn fractions contributing to the ligand-controlled mechanisms. The amount of Zn released within 192 h varied significantly(8–43 mg kg^(-1)), which corresponded to 12%–40% of the total soil Zn, indicating that Zn solubility in most soils was relatively low and that Zn mainly occurred as residual phases. The kinetics of Zn release was well described by the power function model(r = 0.65–0.99, median = 0.87). The magnitude of initial Zn release(coefficient a) was significantly(P soils, the dynamics of which have a significant influence on the availability, phytoextraction, and mobility of Zn in terrestrial and engineered environments.

关键词： ethylenediaminetetraacetic acid kinetic release ligand exchange sequential extraction zinc fraction zinc solubility

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Predicting soil Moisture Characteristic Curves from Continuous Particle-Size Distribution Data

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Pedosphere 2013年第1期23卷 70-80页

作者： M.H.MOHAMMADI F.MESKINI-VISHKAEE department of soil science Faculty of Agriculture University of Zanjan

soil moisture characteristic curve （SMC） is a fundamental soil property and its direct measurement is tedious and time consuming. Therefore, various indirect methods have been developed to predict SMC from particle-size distribution （PSD）. However, the majority of these methods often yield intermittent SMC data because they involve estimating individual SMC points. The objectives of this study were 1） to develop a procedure to predict continuous SMC from a limited number of experimental PSD data points and 2） to evaluate model predictions through comparisons with measured values. In this study, an approach that allowed predicting SMC from the knowledge of PSD, parameterized by means of the closed-form van Genuchten model （VG）, was used. Through using Mohammadi and Vanclooster （MV） model, the parameters obtained from fitting of VG to PSD data were applied to predict SMC curves. Since the residual water content （Or） could not be obtained through fitting of VG-MV integrated model to PSD data, we also examined and compared four different methods estimating 0r. Results showed that the proposed equation （MV-VG integrated model） provided an excellent fit to all the PSD data and the model could adequately predict SMC as measured in forty-two soils sampled from different regions of Iran. For all soils, the method in which Or Was obtained through parameter optimization procedure provided the best overall predictions of SMC. The two methods estimating Or with Campbell and Shiozawa （CS） model resulted in less accuracy than the optimization procedure. Furthermore, the proposed model underestimated the moisture content in the dry range of SMC when the value of 0r was assumed to equal zero. 0r could be attributed to the incomplete desorption of water coated on soil particles and the accurate estimation of 0r was critical in prediction of SMC, especially for fine-textured soils at high suction heads. It could be concluded that the advantages of our approach were the continuity, rob

关键词： fine-textured soils modeling residual water content soil hydraulic properties van Genuchten model

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Application of Kinetic Models in Describing soil Potassium Release Characteristics and Their Correlations with Potassium Extracted by Chemical Methods

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Pedosphere 2013年第4期23卷 482-492页

作者： A. R. HOSSEINPUR H. R. MOTAGHIAN department of soil science College of Agriculture Shahrekord University

Potassium （K） release characteristics in soil play a significant role in supplying available K. Information on K-release characteristics in soils of central Iran is limited. The objectives of this study were to determine K release characteristics and correlations of K release rate constants with K extracted by different chemical methods in surface soils of ten calcareous soils of central Iran. The kinetics of K release in the soils was determined by successive extraction with 0.01 mol L-1 CaC12 in a period of 2-2017 h at 25±1℃. soil K was extracted by distilled water, 0.5 mol L-1 MgNO3, 0.002 mol L-1 SrC12, 0.1 mol L-1 BaC12, 0.01 mol L-1 CaC12, 1 mol L-1 NaC1, 1 mol L-1 boiling HNO3, 1 mol L-1 NH4OAC, Mehlich 1, 0.002 mol L-1 SrC12 ＋ 0.05 mol L-1 citric acid, and ammonium bicarbonate-diethylenetriamine pentaacetic acid （AB-DTPA）. A plot of cumulative amounts of K released showed a discontinuity in slope at 168 h. Thus, two equations were applied to two segments of the total reaction time （2-168 and 168-2 017 h）. Cumulative amounts of K released ranged from 55 to 299 mg kg-1 in 2-168 h and from 44 to 119 mg kg-1 in 168-2 017 h. Release kinetics of K in the two time segments conformed fairly well to parabolic diffusion, simplified Elovich, and power function models. There was a wide variation in the K release rate constants. Increasingly higher average concentrations of soil K were extracted by distilled water, Mehlich 1, SrC12, CaC12, SrC12 ＋ citric acid, AB-DTPA, MgNO3, NaCI, NH4OAc, BaCI2, and HNO3. Potassium release rate constants were significantly correlated with K extracted. The results of this study showed that information obtained from mathematical modeling in two reaction time segments can help to estimate the K-supplying power of soils.

关键词： chemical extraction calcareous soils mathematical modeling release rate constant time segments

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Provenance, Tectonic Setting and Geochemistry of Ahwaz Sandstone Member(Asmari Formation, Oligo-Miocene), Marun Oilfield, Zagros Basin, SW Iran

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Acta Geologica Sinica(English Edition) 2014年第3期88卷 931-948页

作者： Shahram AVARJANI Asadollah MAHBOUBI Reza MOUSSAVI-HARAMI Hassan AMIRI-BAKHTIAR department of geology Faculty of Science Ferdowsi University of MashhadIran department of geology National Iranian south Oil CompanyIran

The Asmari Formation deposited in the Zagros foreland basin during the ***,the Asmari Formation consists of limestone,dolomitic limestone,dolomite,argillaceous limestone,some anhydrite （Kalhur Member） and sandstones （Ahwaz Member）.This study is based on the analysis of core samples from four subsurface sections （wells Mn-68,Mn-281,Mn-292 and Mn-312） in the Marun Oilfieid in the Dezful embayment subzone in order to infer their provenance and tectonic setting of the Ahwaz Sandstone *** data reveal that the Ahwaz Sandstone comprises 97.5% quartz,1.6% feldspar,and 0.9% rock fragments and all samples are classified as quartz *** provenance and tectonic setting of the Ahwaz Sandstone have been assessed using integrated petrographic and geochemical *** analysis reveals that mono-and poly-crystalline quartz grains from metamorphic and igneous rocks of a craton interior setting were the dominant ***,major and trace element concentrations in the rocks of the Ahwaz Sandstone indicate deposition in a passive continental margin *** indicated by the CIW index （chemical index of weathering） of the Ahwaz Sandstone （average value of 82） their source area underwent ＂intense＂ recycling but ＂moderate to high＂ degree of chemical *** petrography and geochemistry results are consistent with a tropical,humid climate and low-relief highlands.

关键词： Asmari Formation Dezful Embayment provenance tectonic setting sandstone,geochemistry Ahwaz Sandstone Member

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Spatial Prediction of soil Aggregate Stability and Aggregate-Associated Organic Carbon Content at the Catchment Scale Using Geostatistical Techniques

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Pedosphere 2011年第3期21卷 389-399页

作者： J.MOHAMMADI M.H.MOTAGHIAN department of soil science Agriculture CollegeShahrekord University

The association of organic carbon with secondary particles （aggregates） results in its storage and retention in soil. A study was carried out at a catchment covering about 92 km2 to predict spatial variability of soil water-stable aggregates （WSA）, mean weight diameter （MWD） of aggregates and organic carbon （OC） content in macro.- （〉 2 mm）, meso- （1-2 mm）, and micro-aggregate （〈 1 mm） fractions, using geostatistical methods. One hundred and eleven soil samples were eSlleeted at the 0 10cm depth and fractionated into macro-, meso-, and mlcro-aggregates by wet sieving. The OC content was determined for each fraction. A greater percentage of water-stable aggregates was found for micro-aggregates, followed by meso-aggregates. Aggregate OC content was greatest in meso-aggregates （9 g kg-1）, followed by micro-aggregates （7 g kg-1）, while the least OC content was found in macro-aggregates （3 g kg-1）. Although a significant effect （P = 0.000） of aggregate size on aggregate OC content was found, however, our findings did not support the model of aggregate hierarchy. Land use had a significant effect （P = 0.073） on aggregate OC content. The coefficients of variation （CVs） for OC contents associated with each aggregate fraction indicated macro-aggregates as the most variable （CV = 71%）. Among the aggregate fractions, the micro-aggregate fraction had a lower CV value of 27%. macro-aggregates to 84% for micro-aggregates. Geostatistical analysis differences in their spatial patterns in both magnitude and space at variance for most aggregate-associated properties was lower than 45%. The mean content of WSA ranged from 15% for showed that the measured soil variables exhibited each aggregate size fraction. The relative nugget The range value for the variogram of water-stable aggregates was almost similar （about 3 km） for the three studied aggregate size classes. The range value for the variogram of aggregate-associated OC contents ranged from about 3 km for macro-aggregates to about

关键词： kriging organic matter variogram water-stable aggregates

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