Morphogenesis of Vertisols：A Model Study

Studies on Vertisols of Southwes China show that the distribution of organic matter,mechanical compositon,carbonates and spore-pollen in their profiles exhibits a definite differentiation and the radiocarbon age has a functional variation with soil depth,which sugests that pedoturbation model is a kind of incomplete model for genetic study and that the distubance and inversion of solums of Vertisol are not as rapid and absolute as expected.In further consideration of the characters of swelling pressure and shear strength of Vertisol,vertic soil and other zonal soils.it is speculated that soil mechanics model is more adaptable for interpreting the morphogenesis of vertisols without any contradiction with soil properties.     

金沙江干热峡谷中退化的土壤生态系统生物学特征初探

Distribution characteristics of soil animals,microorganisms and enzymatic activity were studied in the dry red soil and Vertisol ecosystems with different degradation degrees in the Yuanmou dry hot valley of the Jinsha River,China.Results showed that Hymenoptera,Araneae and Collembola were the dominant groups of soil animals in the polts studied.The numbers of groups and individuals and density of soil animals in the dry red soil series were higher than those in the Vertisol series,and the numbers of individuals and density of soil animals decreased with the degree of soil degradation.Bacteria dominated microbiococnosis not only in the dry red soils but also in the Vertisols.Microbial numbers of the dry red soil series were higher than those of Vertisol series,and decreased with the degree of soil degradation.The activities of catalase,invertase,urease and alkaline phosphatase declined with the degradation degree and showed a significant decline with depth in the profiles of both the dry red soils and the Vertisols,but activities of polyphenol oxidase and acid and neutral phosphatase showed the same tendencies only in the Vertisols.It was concluded that the characteristics of soil animals,microorganisms and enzymatic activity could be used as the bio-indicators to show the degradation degree of the dry red soils and Vertisols.Correlation among these soil bio-indicators was highly significant.     

作物根系层土壤水分模拟的经验-机理模型

To predict soil water variation in the crop root zone,a general exponential recession (GER) model was developed to depict the recession process of soil water storage.Incorporating the GER model into the mass balance model for soil water,a GER-based physicoempirical (PE-GER) model was proposed for simulating soil water variation in the crop root zone.The PE-GER model was calibrated and validated with experimental data of winter wheat in North China.Simulation results agreed well with the field experiment results,as well as were consistent with the simulation results from a more thoroughly developed soil water balance model which required more detailed parameters and inputs.Compared with a previously developed simple exponential recession (SER) based physicoempirical (PE-SER) model,PE-GER was more suitable for application in a broad range of soil texture,from light soil to heavy soil.Practical application of PE-GER showed that PE-GER could provide a convenient way to simulate and predict the variation of soil water storage in the crop root zone,especially in case of insufficient data for conceptual or hydrodynamic models.     

Age and Some Genetic Characteristics of Vertisols in China

The ages of organic matter of some dark-colored horizons and calcareous concretions in some Vertisols from tropical,subtropical and warm-temperate zones of China were studied using radiocarbon dating method.The relationship between soil age and genesis of Vertisols was also expounded based on the study of their genetic characteristics and micromorphological features.The results show that although Vertisols have developed for a relatively long time,their weathering and soil forming process are weak and young with little horizonation.This is closely related to their special grochemical soil forming environment.Low-lying terrain,heavy texture,clay minerals dominated by montmorillonites and alternative drying-wetting climate give rise to the vertic features expressed in intense swelling-shrinking and cracking-closing in soils.As a result,the soil development and soil leaching process are resisted,and the climatic effect on the horizonation is impeded.Moreover,pedoturbation eliminates the horizonation in the upper part of soil profile,and postpones their evolution into zonal soils.So vertisols show certain pedogenic inertia and stay at relatively young developmental stage.Therefore,Vertisols are intrazonal soils dominated by local soil forming factors such as the relief and parent materials.     

基于微观球体颗粒模型的土水特征曲线研究

When variations occur in the water content or dry bulk density of soil,the contact angle hysteresis will affect the soil-water characteristic curve(SWCC).The occurrence of the contact angle hysteresis can be divided into slipping and pinning.It is difficult to determine the effect of pinning existence on SWCC by tests.In this study,the effect of contact angle hysteresis on SWCC was analyzed either in the case of no variations in soil dry bulk density with changes in soil water content or no variations in soil water content with changes in soil dry bulk density.In both cases,soil particles were simplified to the spherical particle model.Based on the geometrically mechanic relationship between the particles and connecting liquid bridges,a physical model for predicting the SWCC was derived from the spherical particle model.Adjusting parameters made the model applicable to various soils,that is,the cohesive soil was considered as micron-sized spherical particles.Through the simulations on SWCC test data of sand,silt,clay,and swelling soil,it was confirmed that the physical model possessed good reliability and practicability.Finally,the analysis of rationality of contact angle was performed based on the basic assumptions of the model.     

A new perspective on functional redundancy and phylogenetic niche conservatism in soil microbial communities

Functional redundancy in soil microbial communities seems to contradict the notion that individual species have distinct metabolic niches in multi-species communities.All soil microbiota have the metabolic capacity for"basic"functions(e.g.,respiration and nitrogen and phosphorus cycling),but only a few soil microbiota participate in"rare"functions(e.g.,methanogenesis and mineralization of recalcitrant organic pollutants).The objective of this perspective paper is to use the phylogenetic niche conservatism theory as an explanation for the functional redundancy of soil microbiota.Phylogenetic niche conservatism is defined as the tendency for lineages to retain ancestral functional characteristics through evolutionary time-scales.The present-day soil microbiota is the result of a community assembly process that started when prokaryotes first appeared on Earth.For billions of years,microbiota have retained a highly conserved set of core genes that control the essential redox and biogeochemical reactions for life on Earth.These genes are passed from microbe to microbe,which contributes to functional redundancy in soil microbiota at the planetary scale.The assembly of microbial communities during soil formation is consistent with phylogenetic niche conservatism.Within a specific soil,the heterogeneous matrix provides an infinite number of sets of diverse environmental conditions,i.e.,niches that lead to the divergence of microbial species.The phylogenetic niche conservatism theory predicts that two or more microbial species diverging from the same clade will have an overlap in their niches,implying that they are functionally redundant in some of their metabolic processes.The endogenous genetic factors that constrain the adaptation of individuals and,thus,populations to changing environmental conditions constitute the core process of phylogenetic niche conservatism.Furthermore,the degree of functional redundancy in a particular soil is proportional to the complexity of the considered function.We conclude with a conceptual model that identifies six patterns of functional redundancy in soil microbial communities,consistent with the phylogenetic niche conservatism theory.     

地膜覆盖滴灌棉田土壤上水分动态的数值模拟

Drip irrigation under plastic mulch has been widely applied in arid Northwest China as a water-saving irrigation technology.A comprehensive knowledge of the distribution and movement of soil water in root zone is essential for the design and management of irrigation regimes.Simulation models have been proved to be efcient methods for this purpose.In this study,the numerical model Hydrus -2D was used to simulate the temporal variations of soil water content in a drip irrigated cotton field under mulching.A concept of partitioning coefcient,calibrated to be 0.07,was introduced to describe the efect of plastic mulch on prevention of evaporation.The soil hydraulic parameters were optimized by inverse solution using the field data.At the optimized conditions,the model was used to predict soil water content for four field treatments.The agreements between the predictions and observations were evaluated using coefcient of determination (R2) and root mean square error (RMSE).The results suggested that the model fairly reproduced the variations in soil water content at all locations in four treatments,with R2 ranging from 0.582 to 0.826 and RMSE from 0.029 to 0.050 cm3 cm-3,indicating that the simulations agreed well with the observations.     

Estimating Soil Salinity in the Yellow River Delta,Eastern China——An Integrated Approach Using Spectral and Terrain Indices with the Generalized Additive Model

Soil salinity is one of the most severe environmental problems worldwide. It is necessary to develop a soil-salinity-estimation model to project the spatial distribution of soil salinity. The aims of this study were to use remote sensed images and digital elevation model (DEM) to develop quantitative models for estimating soil salinity and to investigate the influence of vegetation on soil salinity estimation. Digital bands of Landsat Thematic Mapper (TM) images, vegetation indices, and terrain indices were selected as predictive variables for the estimation. The generalized additive model (GAM) was used to analyze the quantitative relationship between soil salt content, spectral properties, and terrain indices. Akaike’s information criterion (AIC) was used to select relevant predictive variables for fitted GAMs. A correlation analysis and root mean square error between predicted and observed soil salt contents were used to validate the fitted GAMs. A high ratio of explained deviance suggests that an integrated approach using spectral and terrain indices with GAM was practical and efficient for estimating soil salinity. The performance of the fitted GAMs varied with changes in vegetation cover. Salinity in sparsely vegetated areas was estimated better than in densely vegetated areas. Red, near-infrared, and mid-infrared bands, and the second and third components of the tasseled cap transformation were the most important spectral variables for the estimation. Variable combinations in the fitted GAMs and their contribution varied with changes in vegetation cover. The contribution of terrain indices was smaller than that of spectral indices, possibly due to the low spatial resolution of DEM. This research may provide some beneficial references for regional soil salinity estimation.     

淮北平原的变性土的形成和演化

The objectives of the present paper are to restore soil-forming environment of the Vertisols,to reveal their regularities of formation and evolution and to found soil chronology.In regard to formation and evolution of the Vertisols in the Huaibei Plain,they have undergone 3 cycles of deposition-formation during different geologic time (Q3^3;Q4^2 and Q4^3).Therefore,they are considered as the soils developed on heterogeneous parent material.The Vertisols as a paleosol can be divided into relict Vertisols and buried Vertisols.The former is shajiang black soils called by local people,the latter is shajiang black soils underlying Warp soil or warp soil horizon.     

Mechanistic Model for Predicting NO3-N Uptake by Plants and Its Verification

Some mechanistic models have been proposed to predict the No3^- concentrations in the soil solution at root surface and the NO3-N uptake by plants,but all these relatively effective non-steady state models have not yet been verified by and soil culture experiment.In the present study,a mathematical model based on the nutrient transport to the roots,root length and root uptake kinetics as well as taking account of the inter-root competition was used for calculation,and soil culture experiments with rice,wheat and rape plants grown on alkali,neutral and acid soils in rhizoboxes with nylon screen as a isolator were carried out to evaluate the prediction ability of the model through comparing the measured NO3-concentrations at root surface and N uptake with the calculated values.Whether the inter-root competition for nutrients was accounted for in the model was of less importance to the calculated N uptake but could induce significant changes in the relative concentrations of NO3^- at root surface.For the three soils and crops,the measured NO3-N uptake agreed well with the calculated one,and the calculated relative concentrations at root surface were approximate to the measured values.But an appropriate rectification for some conditions is necessary when the plant uptake parameter obtained in solution culture experiment is applied to soil culture.In contrast with the present non-steady state model,the predicted relative concentrations,which show an accumulation,by the Phillips‘ steady-state model were distinct from the measured values which show a depletion,indicating that the present model has a better prediction ability than the steady-state model.     

Nitrogen and Carbon Mineralization in Cultivated Acrisols and Vertisols in a Sub-Humid Tropical Climate

In the southern part of the Republic of Benin (West Africa), investigations were carried out on two contrasting sites (Ferrali-Haplic Acrisols and Stagni-Eutric Vertisols), with the aim of assessing the effect of soil type and micro-climate on carbon and nitrogen turnover under subhumid tropical conditions. The Acrisols in Southern Benin are characterized by a sandy topsoil with high water permeability. In contrast, the Vertisols have a clayey topsoil and show stagnic properties. Maize was planted during two years i.e. four consecutive cropping seasons (no-till, no organic or mineral fertilizer, weeding by hoe) on a total of fourteen Acrisol and nine Vertisol plots. Fresh organic material like fallow vegetation or crop residues were systematically removed. In spite of their higher clay content the Vertisols showed significantly higher carbon mineralization rates (12.0%) under field conditions than Acrisols (5.2% of C_org per year). The net nitrogen mineralization rates were, however, similar on both sites (13.8% and 13.0% of N₁ per year respectively). Differences between Vertisols and Acrisols were due to the drier microclimate in the Acrisols. Incubation studies with Acrisol topsoil samples under controlled conditions demonstrated that decreasing soil matrix potential and temperature fluctuations, as they occur in the field, reduce CO₂ evolution more than the net nitrogen mineralization, which was not the case in Vertisol topsoil samples. Carbon mineralization is, therefore, under tropical sub-humid conditions highly related to soil microclimate, hence site specific. Carbon and nitrogen mineralization may differ considerably from each other depending on site conditions.     

Palygorskitreicher Vertisol im ariden Bereich NO-Somalias

Palygorskite rich Vertisol in the arid part of NE-Somalia In the arid part of NE-Somalia on a large plane in the central part of the Darror Valley Vertisols rich in palygorskite are found. The investigated Vertisol is very poor on smectite and vermiculite. The parent material of the soil consists of Pleistocenic fluvial sediment, which originated from Tertiary stones. In the field, slicken sides in 92 to 140 cm depth and cracks reaching a depth of 100 cm were observed in the soil. The cracks were partly filled with topsoil material. Because of the fresh appearance of gilgai microrelief and the cracks, which are partly empty, peloturbation must be active under the present climatic conditions. The high content of palygorskite in the investigated Vertisol seems to be lithogenic and originating from Tertiary sediments found in the surrounding area.     

The genesis of vertisols with gilgai microtopography: A review

Different hypotheses about the genesis of gilgai microtopography and corresponding soil complexes with clayey swelling soils are considered in this review. Their diversity is stipulated by specificities of the objects themselves and by the history of studies of the composition, properties, regimes, and landscape conditions of the areas with Vertisols in different countries. Most of the hypotheses about the genesis of Vertisols with the gilgai microtopography suggest that strong swelling–shrinking processes take place in these soils in the course of moistening–drying cycles; the origin of shear stress in the soils, its spatial patterns, and the particular ways of translocation of the soil material are discussed. At the early stage of Vertisol studies, a hypothesis about the leading role of the process of “self-swallowing” of the soils as a result of filling of open cracks with the material from the upper soil horizons was popular. However, numerous facts suggest that the intensity of this process is relatively low, so that it cannot play the major role in the gilgai formation and cyclic changes in the thickness and properties of the soil horizons in Vertisols. Another important mechanism is the uneven moistening and drying of the whole soil volume resulting in the irregular distribution of inner tensions in the soil with the development of shear stress and plastic deformation of the soil mass. The hypotheses suggested in the recent decades are based on the models of soil mechanics. A number of hypotheses consider possible alternation and duration of evolutionary stages of the development of Vertisols with the gilgai microtopography.     

Crop Residue Retention and Nutrient Management Practices on Stratification of Phosphorus and Soil Organic Carbon in the Soybean–Wheat System in Vertisols of Central India

The long-term crop residue retention coupled with external nutrient inputs are crucial for maintaining soil phosphorus (P) and soil organic carbon (SOC) in Vertisols of Central India. A study was conducted to evaluate the long-term effect of three wheat residue management practices (residue burning, incorporation, and surface retention) in combination with three supplementary nutrient inputs (SNI) [control, fertilizer, and farmyard manure (FYM)] on stratification of P and SOC in the soybean–wheat system in Vertisol. The wheat residue either incorporated or retained on the soil surface increased the availability of P and SOC content as compared to the common practices of residue burning. Residue retention or incorporation increased stratification of P and soil organic carbon over the residue burning. Irrespective of the nutrient treatments, greater stratification ratio of SOC and P were registered under wheat residue incorporation or retention compared to residue burning. It is evident from the study that wheat residue incorporation or retention plus addition of FYM could be an effective strategy for increasing the soil fertility in a soybean–wheat system of Vertisols of Central India.     

Sources and distribution of arsenic in agricultural soils of Central Mexico

Purpose

The concentrations and distribution of arsenic (As) in two different soil types (Vertisols and Entisols) of Central Mexico impacted by mine activities and irrigation with As-rich groundwater are analyzed in order to determine their impact on the soil quality, and to contribute reliable data that may help to assess the environmental risk that represents the progressive accumulation of As in the arable soils of Guanajuato.

Materials and methods

Two Entisol and two Vertisol profiles located in the Guanajuato state (Mexico) were described and sampled from ~?1.20-m-deep pits. Soils are irrigated with As-rich deep and shallow groundwaters that were sampled from irrigation boreholes. Additionally, a Vertisol profile located in a parcel not impacted by irrigation was sampled and used as a control soil. Minerals were identified by X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with dispersive X-ray spectrometry (EDS). Geoaccumulation indexes (Igeo) were calculated to evaluate As enrichment with respect to a control soil and the Upper Continental Crust (UCC). Anions and cations of groundwater were analyzed by high-performance liquid chromatography (HPLC) and by inductively coupled plasma atomic emission spectroscopy (ICP-AES), respectively. As in soils was determined by ICP-AES.

Results and discussion

Near total As concentrations are higher in Entisols (mean As value?=?7.20 mg/kg) than in Vertisols (mean As?=?1.02 mg/kg). As concentrations in the control soil are lower (0.34 to 0.70 mg/kg). The in-depth distribution of As in Vertisol profiles reveals that the higher As concentrations are found in the uppermost horizons (10 cm) and they tend to decrease with depth. In Entisols, As concentrations do not follow a vertical trend. Igeo values of As indicate moderate to heavy As contamination in Vertisols and moderate contamination in Entisols. SEM-EDS analyses revealed the presence of some potential As-bearing minerals such as magnetite and abundant Fe oxides and Ti-Fe coatings precipitated onto feldspar grains, particularly in Entisols.

Conclusions

Irrigation of Vertisols with As-rich groundwater determines As concentrations in the uppermost horizons that exceed the natural background of the region (0.4 mg/kg). In depth, clay grain-sized particles inhibit the downward migration of As, while Fe oxides and organic matter scavenge As by adsorption. As concentrations in Entisols are higher, and the in-depth distribution of this element is controlled by periodic contributions of As-bearing minerals delivered from mine prospects located at the river’s catchments.

     

Applying Composted Cotton Gin Trash to a Vertisol in Southeastern Queensland,Australia

Many Australian cotton farmers are interested in using organic waste products such as composted cotton gin trash as soil amendments because of perceived benefits to soil health and the environment. However, detailed information on the relative benefits and costs involved is not readily available to cotton growers who farm on clayey Vertisols. The objective of this study was to quantify soil changes in a farmer-established trial to evaluate the potential benefits of applying composted cotton gin trash and/or lime to a Vertisol. Selected soil properties were measured in an experiment located on a commercial cotton farm near Goondiwindi in southern Queensland, Australia. Cotton gin trash compost improved potassium availability and soil microbial biomass in soil, whereas lime improved only the latter.     

滇桂地区变性土的发生特性和系统分类研究

本文研究了我国西南地区变性土的形成条件和发育程度，并结合世界主要分类系统进行了分类研究。结果表明，相对于地带性土壤而言，变性土风化成土作用较弱，发育程度较低，土壤中元素的淋溶迁移及相对富集程度也远低于地带性土壤。由于粘粒含量尤其是粘粒矿物组成的差异，变性土表现出极高的膨胀潜势。通过研究，本文还对我国土壤系统分类中变性土土钢、亚纲、土类等的划分标准和依据及变性土性土的确立等提出了见解。     

The prospects of reduced tillage in tef (Eragrostis tef Zucca) in Gare Arera, West Shawa Zone of Oromiya, Ethiopia

Soils in Ethiopia are traditionally ploughed repeatedly with an oxen-drawn plough before sowing. The oxen ploughing system exposes the soil to erosion and is expensive for farmers without oxen. This study was undertaken to assess agronomic and economic impacts of alternative, reduced tillage methods. Field experiments were carried out on a Vertisol and a Nitisol for 2 years to study the effect of zero tillage, minimum tillage, conventional tillage, and broad bed furrows (BBF) on the yield of tef (Eragrostis tef Zucca). No significant differences in tef biomass and grain yields were observed between the treatments on both soils in the first year. In Nitisol in the second year, yield was lower in the zero tillage treatment as compared to the other treatments. No difference in yield was observed between single plough, conventional, and BBF. On Vertisol, the yields were higher in BBF as compared to the other treatments. The yields on Vertisol were 1368, 1520, 1560 and 1768 kg ha⁻¹ for the zero tillage, minimum tillage, conventional tillage and BBF treatments respectively. More than twice as much grass weed was observed on zero tillage treatment as compared to the BBF treatment on both soils. Zero tillage gave the lowest gross margin on both soils whereas BBF gave the highest gross margin. The gross margin on Nitisols for the zero tillage and BBF treatments were −108 and 1504 Birr/ha respectively and corresponding numbers for the Vertisol were 520 and 1924 Birr ha⁻¹. On Vertisol there were no significant difference in gross margin between minimum tillage and conventional tillage. Minimum tillage is an interesting option on Vertisols, particularly for female-headed households as it reduces the tillage cost. It may also improve overall productivity of the farming system because it allows partial replacement of oxen with cows and reduces soil erosion.