ANN‐based pedotransfer and soil spatial prediction functions for predicting Atterberg consistency limits and indices from easily available properties at the watershed scale in western Iran

Atterberg consistency limits (liquid limit, LL; plastic limit, PL; shrinkage limit, SL) and indices (plasticity index, PI; friability index, FI) are useful indicators of soil mechanical behaviour. This study was conducted to evaluate the use of soil and environmental data for predicting Atterberg limits or indices using artificial neural network (ANN) models at the watershed scale in western Iran. The LL, PL, SL, PI, FI, particle size distribution, organic matter (OM) and calcium carbonate equivalent (CCE) were measured in soil samples collected from 113 locations. Three sets of readily available properties were employed as inputs. The first of these data sets or models consisted of soil properties. The second included topographic attributes and normalized difference vegetation index (NDVI), and the third was a combination of soil, topographic attributes and NDVI. Developed ANN models could explain a majority of the variability (62–94%) in Atterberg limits and indices. Greatest and poorest performances were attributed to the third and first models, respectively. No significant efficacy difference was observed between the second and third models. Therefore, the second data set with its readily available environmental variables is suggested for use in predicting Atterberg limits and indices at the regional scale. Sensitivity analysis showed that NDVI, OM, clay content, CCE and topographic attributes (wetness index, elevation, plan curvature and slope) could explain much of the variance associated with Atterberg limits and indices at the watershed scale in western Iran.     

THE CHARACTERIZATION OF SOME SCOTTISH ARABLE TOPSOILS BY AGRICULTURAL AND ENGINEERING METHODS

Samples from fifty-eight arable topsoils in south-eastern Scotland were analyzed for compactability, plasticity, organic matter content, particle density, and particle-size distribution. The samples were classified by the methods employed for engineering soils and the groupings so obtained were compared with the textural classes. The criteria for the classification of engineering soils provide useful information on the likely mechanical behaviour of arable soils in the field. Tests were made for correlation between fifteen soil properties. The organic matter content, which in the samples studied ranged from 2 to 10 per cent, was shown to influence several mechanical properties, including optimum moisture content, maximum dry bulk density, liquid limit, and plastic limit. Maximum bulk density and optimum moisture content were strongly correlated with Atterberg limits and organic matter content. The liquid limit was more closely correlated with particle-size distribution than was the plastic limit. Unlike soils encountered in engineering, the particle density of these soils was not correlated with particle-size distribution but, like the Atterberg limits, was strongly correlated with organic matter content.     

Guidelines for safe trafficking and cultivation, and resistance–density–moisture relations of three disturbed soils from Alberta

The Atterberg limits and the Proctor compaction test are used by engineers for classifying soils and for predicting stability of building foundations. Field capacity and wilting point (agronomic limits) are used to indicate available water for plant uptake. Few studies have related the engineering criteria to the agronomic ones with regard to compaction hazard for soils. This study investigated the relationships between Atterberg limits, agronomic limits and the critical moisture content (moisture content at Proctor maximum density) for three disturbed soils (sandy loam and clay loam soils from a reclaimed Highvale mine site, and a silt loam soil from a grazing site at Lacombe) of different textures. Relationships between bulk density, moisture content and penetration resistance for these soils were also investigated. For the sandy loam and loam soils, the field capacity was close to the critical moisture content but lower than the plastic limit. Therefore, cultivation of these two soils at moisture contents close to field capacity should be avoided since maximum densification occurs at these moisture contents. Overall, the critical moisture content or field capacity would be a better guide for trafficking of sandy loam and loam textured soils than the Atterberg limits. For the clay loam, field capacity was within the plastic range. Thus trafficking this soil at field capacity would cause severe compaction. In conclusion, either field capacity or plastic limit, whichever is less, can be used as a guide to avoid trafficking at this moisture content and beyond. For the sandy loam and loam soils penetration resistance significantly increased only with increased bulk density (P≤0.05). For the clay loam soil, penetration resistance was positively related to bulk density and negatively related to moisture content.     

Critical-state soil mechanics parameters and their variation for Vertisols in eastern Australia

Compression and shear tests were conducted on undisturbed samples from a range of Vertisols to determine the critical-state parameters, their variation, and the relationships between these parameters and the moisture content and density of the soil. The soils varied considerably in their characteristics, with the liquid limit ranging from 0.39 to 0.88, and were tested over a wide range of moisture contents, densities and saturations. The critical-state parameters describing compressional and shear properties varied with the moisture content, Atterberg limits and density of the soil, in contrast to saturated soils where these parameters are considered to be constants. It was found that the liquidity index (moisture content expressed as fractional distance between the liquid and plastic limits) explained the data significantly better than moisture content and also significantly better than did the suction. These data, therefore, supported suggestions that the Atterberg limits may serve as a useful basis for practical soil management guidelines. The measured parameters displayed considerable variation, demonstrating that any such guidelines need to be cast in terms of probabilities. The soil expanded when sheared if the normal stress during shear was less than about half the pre-consolidation stress and compressed when sheared if the normal stress during shear was more than about half the pre-consolidation stress. This behaviour was repeatable.     

花岗岩红壤丘陵区崩岗土体界限含水量的温度效应研究

水分和温度会显著影响花岗岩红壤的力学状态,是崩岗发生和发展的两大驱动因素.以崩壁三个土层土壤:红土层、砂土层和碎屑层为研究对象,在15、25、40和60℃温度条件下对三个土层土壤的液塑限和结合水含量开展研究.结果表明:红土层的液限、塑限和塑性指数均高于砂土层和碎屑层,碎屑层土壤的液塑限最小.崩岗土壤的液塑限与细黏粒、有...     

Soil Shrinkage Characteristics as Affected by Solution Composition and Mineral Contents

Soil-shrinkage characteristics affect fluid transport and soil mechanical properties, with broad implications for environmental flows, crop production, and civil engineering designs. We quantified mild-saline-solutions effects on soil shrinkage curves and developed pedotransfer functions to predict curve parameters. Seven soil and soil mixes were equilibrated with solutions of 0.5-to-8 dS m^?1 and 0-to-20 sodium adsorption ratios (SAR). Saturated paste rods were dried; water contents and isotropic shrinkage measured. Texture affected shape-forming factors when clay and smectite contents were >260 and 140 g kg^?1, respectively. Solutions ≥2 dS m^?1 affected the coefficient of linear extensibility for smectitic soils containing clay ≥300 g kg^?1. Solution SAR affected only the highest clay content (530 g kg^?1) and mixed mineralogy soils. However, the solution salinity levels were not high enough to affect shape factors of the shrinkage curves. Pedotransfer functions successfully described soil shrinkage with root-mean-squared-errors 1 to 4 magnitudes lower than the highest measured values.     

Plasticity,Mineralogy, and WRB Classification of Some Typical Clay Soils along the Two Major Rivers in Croatia

Eurasian Soil Science - Quantification of soil plasticity is usually based on Atterberg limits or indices, which are then used for engineering and agricultural purposes on clay soils. Because these...     

Genesis and micromorphology of loess-derived soils from central Kansas

The genesis and micromorphology of three Harney soils from different precipitation regions (from 540 mm to 715 mm) (fine, smectitic, mesic Typic Argiustolls) in the Smoky Hills of central Kansas were investigated. The objectives were to (1) examine the morphological, chemical, physical and mineralogical characteristics of Harney soils formed in loess; (2) determine the clay mineral distribution with depth and the origin of the clay minerals present; and (3) investigate the relationship between the clay mineralogy and other soil properties such as soil plasmic fabric, COLE values and fine clay/total clay ratios. Mineralogical and micromorphological techniques were used to evaluate the characteristics of the loess-derived soils. The first pedon was formed in 88 cm of Bignell loess over Peoria loess and the other two pedons were formed from Peoria loess. The chemical properties were similar for the pedons studied. Differences were observed in physical properties, especially in particle size distribution, oven-dry bulk density and coefficient of linear extensibility values. Although the soils were mapped in the same soil series, the geomorphic positions of the pedons and the nature of the parent material affected the characteristics of the soils. Smectite was the predominant clay mineral, especially in the fine clay fraction, regardless of the location in the precipitation gradient. The dominance of smectite increased in the C-horizons. This implies a detrital source of smectite in the B-horizons formed in both Bignell and Peoria loess units. The presence of randomly interstratified mica-smectite and the micromorphological observations of weathering biotite indicate that weathering also plays an important role in the mineralogy of Harney soils. The high content of clay mica in the surface horizons was caused by dust fall in the study area. Thick and continuous argillans were observed when FC/TC and COLE values were low and crystalline smectite was present. In the lower part of the soil profiles, the plasmic fabric was mostly ma-skelsepic (granostriated b-fabric) and smectite was more crystalline as indicated by sharper X-ray diffraction peaks.     

Field studies to assess the workable range of soils in the tropical zone of Veracruz, Mexico

In the tropical area of Veracruz (Mexico) the decision of when and how to carry out tillage operations is based on qualitative criteria. It often results in excessive and unnecessary work, energy waste, operational delay, soil exposure to water erosion and soil structural damage. Objective criteria are needed in this area for selecting when and how to do cultivation in order to meet crop and conservation requirements. The workable range of typical soils of the area (Haplic Pheaozems) was quantified by assessing in-field implement effects on the soil structure and measuring the specific energy applied by the tractor–implement combination. This was done over a range of soil moisture contents inside and outside the theoretical friable consistency state of the soils, determined by the shrinkage and plastic limits. Empirical relationships between initial moisture content and the technological result of tillage showed that these results for moist loam and clay soils shifted from optimum to poor at soil water potentials that coincides quite well with the plastic limit. However, as soil was drying out, the implement effect changed from optimum to sub-optimum at soil moisture contents well above the shrinkage limit, so the actual field workable range was smaller than the theoretical friable status of the soils. The minimum input of specific energy to obtain optimum results, was close to the soil water potential where results changed to sub-optimum as soils were drying out. To support decisions for tillage planning and operation, valuable information on workable periods can be obtained by making use of quantified workability thresholds.     

Soil hydraulic and physico-chemical properties of Ultisols and Inceptisols in south-eastern Nigeria

Understanding soil water dynamics and storage is important to avoid crop failure on highly weathered, porous and leached soils. The aim of the study was to relate soil moisture characteristics to particle-size distributions and chemical properties. On average, Atterberg limits were below 25% in the A-horizon and not more than26.56% in the B-horizon, whereas soil bulk density was between 1.27 and 1.66Mgm^?3. The saturated hydraulic conductivity (K_sat) was generally between 0.20 and 5.43 cm h^?1 in the top soil and <1.31 cm h^?1 in the subsoil. The higher K_sat values for the A-horizons were attributed to the influence soil microorganisms operating more in that horizon. The amount of water retained at field capacity or at permanent wilting point was greater in the B-horizons than in the A-horizons, suggesting that clay accumulation in the B-horizon and evapotranspiration effects in the A-horizon may have influenced water retention in the soils. Soil moisture parameters were positively related to clay content, silt content, exchangeable Mg²⁺, Fe₂O₃ and Al₂O₃, and negatively related to sand content, SiO₂, sodium absorption ratio, exchangeable sodium percentage and bulk density. The low clay content may explain why drainage was so rapid in the soils.     

THE EFFECT OF SOIL COMPOSITION AND ENVIRONMENTAL FACTORS ON THE SHRINKAGE OF SOME CLAYEY BRITISH SOILS

The shrinkage potential of natural clods from a variety of clayey soils was measured and related to their physical, chemical and mineralogical properties. It is shown that the most important factors affecting shrinkage are initial bulk density, clay content, organic carbon content and cation exchange capacity of the peroxidised clay, and mica-smectite content on a whole soil basis. Multiple regression equations involving the initial bulk density, clay content, organic carbon and cation exchange capacity accounted for 87 and 82 per cent of the variation in total shrinkage of topsoils and subsoils respectively. Because of restrictions on shrinkage imposed by factors such as climate, crops, ground-water and moisture release characteristics of soils, soils with a high shrinkage potential may not behave very differently to soils with a much lower potential. On these grounds it is concluded that the shrinkage criteria used in US Taxonomy are not applicable in Britain.     

盐化和有机质对土壤结构稳定性及阿特伯格极限的影响

对甘肃景电灌区盐化和有机质对土壤团聚体的稳定性、黏粒的分散性及阿特伯格极限进行了调查研究。研究结果表明该灌区盐化土壤中水溶性盐以钠盐为主,土壤具有钠质现象。随含盐量和交换性钠离子百分率（ESP）的增加土壤团聚体的稳定性显著降低,黏粒的分散性显著增加,阿特伯格极限具有降低的趋势,明确地说明盐化和伴随着的钠质化是土壤结构性能退化的主要原因。随有机质含量的增加,土壤团聚体的稳定性显著增加,黏粒的分散性显著降低,阿特伯格极限显著增加,说明增加有机质含量可以显著改善盐化土壤的结构性能。可以根据如下公式利用有机质含量（OM）和ESP预测团聚体的稳定性:WSAR=19.4 0.98OM-1.43 ESP（R2=0.5741,n=67）。团聚体稳定性、黏粒分散性、流限和塑限互相之间显著相关,说明流限和塑限可以作为反映盐化土壤结构状况的指标。     

Contemporary pedogenetic processes in a ferrallitic soil in Uganda,I. Identification

Ferrallitic soils were originally considered to be pedogenetically “dead”, with few pedological processes taking place except perhaps leaching. A study of the Buganda clay loam series, a widespread soil in southern Uganda, showed that although this ferrallitic soil is very highly weathered chemically, two important groups of pedogenetic processes are currently active, differentiating the B from the C horizon. These are alteration of soil structure/physical properties and clay translocation. Leaching and clay mineral transformation are not occurring. It is suggested that the pedogenetic basis for classifying soils as ferrallitic has become outdated and that the criteria used need revision.     

Influence of load on shrinkage behavior of peat soils

The shrinkage of the peat soils that accompanies the soil moisture changes is an important feature of such soils and has strong influence on their physical attributes and soil water management. The relationships between soil moisture and volume are often described using shrinkage characteristic curves by relating void ratio (volume of voids per unit volume of solids) to moisture ratio (volume of water per volume of solids). For conversion of soil volume changes into cracks volume and subsidence, a dimensionless shrinkage geometry factor is used. The paper presents results of volumetric shrinkage behavior and the geometry factor at various loads in sedge and alder peat soils. The measurements were conducted on undisturbed soil samples without applying a load and with loads corresponding to field overburden. The shape of the shrinkage characteristics of such soils were completely different from those of clay soils. The application of loads did not significantly influence the shrinkage characteristics curve. The applied load strongly influenced on relationship between shrinkage geometry factor and the moisture ratio, showing higher values of subsidence and lower values of crack volume in comparison with unloaded conditions.     

Improved prediction of water-retention properties of clayey soils by pedological stratification

The water-retention properties of clayey soils have been studied at ?0.3 × 10⁵ and ?15 × 10⁵ Pa matric potentials using three sets of clayey horizons differing in their pedological origin. Measurements were made on small clods collected in winter when swelling is at a maximum. The results are discussed in relation to variations in the clay content and clay fabric. The bulk volume, which appears to be closely related to both clay content and clay fabric, allows the variations in water retained to be explained better than with clay content alone. With clayey horizons originating from a single soil family, differences in water retained can be explained by variations in clay content alone because clay fabric does not change greatly. These results demonstrate the significance of pedological stratification in estimating the water-retention properties when a single soil characteristic, such as clay content, is used.     

Physical properties and moisture retention characteristics of some nigerian soils

Measurements were made of physical characteristics of 119 samples from 23 profiles derived from two parent materials in Nigeria. The laboratory analyses included texture, plasticity and shrinkage characteristics, and a range of soil moisture constants including saturation point and moisture retention at various suctions. Simple and multiple correlation coefficients and regression analyses were conducted to investigate the possibilities of obtaining estimates of soil moisture retention from the textural analysis. Clay and sand contents are correlated with various soil moisture constants. The textural analysis may therefore be used to estimate moisture holding capacity at different suctions for these and similar soils with a predominantly uniform clay mineralogy, dominated by kaolinite and sesquioxides. Moisture retention curves indicate that the “field capacity” for most of these soils is better estimated at 60 or 100 cm of water suction rather than at 0.3 bar. A plot of the pF curves indicated only slight differences between moisture retention at 2 or 3 bar suction and at 15 bar suction.     

Depositional seals in polyacrylamide-amended soils of varying clay mineralogy and texture

Purpose  

Depositional seals, formed when turbid waters infiltrate into soils, lead to a reduction in soil hydraulic conductivity (HC) and enhance runoff and soil erosion. Since clay size particles constitute a dominant proportion of depositional seals, soil texture and clay mineralogy play a significant role in determining the seal’s hydraulic characteristics. Presence of high molecular weight anionic polyacrylamide (PAM) in suspension flocculates fine sediments, and therefore, its application to the soil surface may modify the characteristics of the depositional seal. The impact of PAM on the latter is expected to be influenced by soil properties. The aim of this study was to elucidate the effects of PAM application on clay flocculation and the HC of depositional seals formed in four soils varying in texture (ranging from loamy sand to clay loam), and diverse proportions of clay mineral constituents (kaolinite, smectite, and vermiculite).     

AGE HARDENING OF AGRICULTURAL TOP SOILS

Changes in the strength of remoulded agricultural top soil with ageing are studied for two sandy loam soils from South Australia and a clay soil from Queensland. There is evidence of significant thixotropic behaviour in these soils around the water contents at which tillage is usually performed. For the Urrbrae soil, in which the dominant clay minerals are illite and kaolinite. the maximum thixotropic strength ratio was obtained at a water content just below the plastic limit. For the Strathalbyn soil, which contains illite and actinolite. and for the Waco soil which contains montmorillonite. the maximum thixotropic strength ratios occurred at water contents between the plastic and liquid limits. The age hardening for these soils was investigated using probe penetration, tensile strength and compression resistance measurements. The effect was still apparent after sterilization and after removal of organic matter.     

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。