Mycelial bacteria of saline soils

The actinomycetal complexes of saline soils comprise the representatives of the Streptomyces and Micromonospora genera, the number of which are hundreds and thousands of CFU/g soil. Complexes of mycelial bacteria in saline soils are poorer in terms of number (by 1–3 orders of magnitude) and taxonomic composition than the complexes of the zonal soil types. A specific feature of the actinomycetal complexes of saline soils is the predominance of halophilic, alkaliphilic, and haloalkaliphilic streptomycetes that well grow at pH 8–9 and concentrations of NaCl close to 5%. Actinomycetes in saline soils grow actively, and the length of their mycelium reaches 140 m in 1 gram of soil. The haloalkaliphilic streptomycetes grow fast and inhibit the formation of spores at pH 9 and high concentrations of salts (Na₂SO₄ and MgCl₂, 5%) as compared to their behavior on a neutral medium with a salt concentration of 0.02%. They are characterized by the maximal radial growth rate of colonies on an alkaline medium with 5% NaCl.     

Microflora of extreme arid Atacama Desert soils

Surface and subsurface soil samples from the most arid region within the Atacama Desert, Chile, were analyzed for total organic carbon (TOC), phospholipid fatty acids (PLFA) and culturable bacteria. TOC content was determined to range between 560 and 765 μg/g. PLFA analysis indicated 2.0×10⁶-1.0×10⁷ cell equivalents/g. Culturing of soil extracts on R2A and TSA media yielded 1.6×10³-4.6×10³ CFU/g, and 200-300 CFU/g heat shock survivors. Twenty isolated strains were identified based on analysis of 16S rRNA gene sequences, and divided into eight phylogenetic groups, including Rhodopseudomonas, Sphingomonas sp., Mesorhizobium sp., Asticcacaulis sp., Bradyrhizobium sp., Bacillus subtilis, Bacillus pumilus, and Burkholderia sp.     

Improvement of saline soils through indigenous materials

Reclamation of saline soils involves heavy leaching with water, with or without the addition of gypsum, depending upon the calcium content of the soil. Many a time, flushing the soil becomes difficult because of its low permeability due to high clay content, as obtained in most of the coastal saline soils of India. There is also the danger of hydrolysis under conditions of prolonged leaching, which may result in raising the pH, dispersion of the soil, impeded drainage, root penetration and aeration. Reclamation of such soils, therefore, calls for the improvement of physical conditions for better permeability and addition of calcium rich substances. Indigenous materials like basic slag, lime sludge, calcareous soil and iron rich mineral soil, in addition to gypsum, may serve as useful amendments for improving the soil's physical conditions. It was, therefore, thought worth-while to study the effect of addition of these materials on the improvement of saline soils.     

Sorption and fate of perchlorate in arid soils

The mobility of perchlorate in soils depends on several factors, including soil mineralogy and the presence of other oxyanions that compete with perchlorate for the retention sites. Currently, there are no studies that evaluate the mobility of perchlorate in arid soils. The present study evaluated the mobility of ClO₄^– in three arid soils, Canchones, Humberstone and Pica, exposed to two ClO₄^– concentration ranges and different ionic strengths. In Humberstone (non-agricultural) and Pica (agricultural) soils, the sorption processes were not important for both concentration ranges, while Canchones soil (agricultural) showed a decrease in perchlorate concentration associated with microbial degradation processes. The increase of medium ionic strength by addition of Ca(NO₃)₂ only had an important effect on Humberstone soil, associated with the presence of kaolinite and muscovite (variable charge). A competition effect was observed between perchlorate, nitrate and other anions presents in solution by absorption sites generated from variable charge mineral and calcium. Considering the quite low sorption capacity of the soils and the high solubility, perchlorate can be absorbed by fruit and vegetables of export in concentrations over the healthy levels established by international organization.     

Mycelial fungi in saline soils of the western Transbaikal region

Mycelial fungi in a solonchakous chestnut soil, a sulfate solonchak, and a soda solonchak were studied in the western Lake Baikal basin. The humus content, the degree of salinization, and the composition of salts affected the structure of the micromycete communities. In the chestnut soil, more than half of the species identified were found. The species diversity was higher in the nonsaline and humus horizons. The eolian deposit on the soda solonchak was characterized by the presence of six species of fungi that did not occur in other soil horizons. Their occurrence in the fresh deposit seems to be related to the eolian transfer of fungi with the fine earth from the adjacent areas with the nonsaline soils. The soda solonchak fungi are dominated by the haloalkalitolerant and alkalophilic micromycetes, among which the representatives of the Acremonium (A. antarcticum and A. rutilum) and Verticillum genera and Mycelia sterilia were identified. There was also an alkalophilic ascomycete, which is an indicator of soda salinization??Heleococcum alkalinum. On the whole, the soda solonchak had the lowest number of fungal germs and the lowest species diversity of mycelial fungi among the soils compared.     

Assessing the degradation of saline wetlands in an arid agricultural region in Spain

A constellation of saline wetlands in the Spanish Monegros Desert is currently subjected to increasing agricultural pressure. Until now, no systematic study of their degradation status has been performed, and no comprehensive map of these wetlands has been available. Both subjects are addressed for the first time in this study. In addition, we set up a conceptual tool for assessing saline wetlands degradation that improves upon available methods within geomorphological, sedimentological or hydrological frameworks. A wetlands inventory was produced and updated using satellite data, field observations, and orthophotographs, together with the available disperse data about these wetlands' toponymy and location. The degraded landscape appearance of the surviving wetlands, mainly affected by agricultural intensification ― dumping and farming ― has been qualitatively assessed.     

Impact of carbo-gaseous saline waters registered by soils

The impact of carbo-gazeous saline spring waters, rich in Ca, Fe, As and P and chemically stable through time, on the chemistry (major and trace elements) and mineralogy of soils developed from anatexite is presented. The soils developed beyond the influence of the spring are typical of a granite pedogenesis on a granitic bedrock with Ca loss, Si, Al and K conservation. The soils influenced by the springs are enriched in Ca and Fe, respectively, precipitated as carbonates and oxides. In such soils, the presence of two Ca-enrichment peaks may be explained by the occurrence of two distinct precipitation mechanisms for the carbonates: (1) related to degassing of the carbo-gaseous waters upon emergence at the surface, and (2) in the water-unsaturated zone, related to capillary rise and evaporation processes. The precipitation of iron oxides is related to a change in the redox potential of the mineral waters, following their emergence at the surface.The simultaneous association of As+P with Fe, as evidenced by principal components analysis and in the patterns in concentrations vs. depth observed in soils, can be explained by adsorption and/or coprecipitation of As and P during iron-oxide formation, while The As and P enrichments and the carbonate formation are independent.The extent of the spring influence was studied: the soil enrichments in Ca and, particularly, Fe sharply decrease with increasing distance from the spring on a metric scale.     

Potassium release in some saline soils of Israel

Potassium release from samples of two saline and three nonsaline soils was studied by measuring the amounts of the cation in 0.01 N CaCl₂ and water extracts. The factors which affected the release were: the distribution of potassium between the silt and clay fractions, the total potassium content of the sample and its salinity. Soil samples with a distribution ratio above unity (i.e., with potassium mainly in the silt fraction) and a high total potassium content released K at a higher rate than those with a distribution ratio below unity and a high total potassium content. The effect of salinity was of minor importance in comparison with those of the two other factors.     

Inclusion of soils and soil-like bodies of urban territories into the Russian soil classification system

The results of the Internet discussion on the classification of urban soils aimed at evaluating their possible inclusion into the modern Russian soil classification system adopted by a wide range of specialists are presented. The first step was to address the urban diagnostic horizons as the basis for identifying soil types according to the rules of the Russian soil classification. New diagnostic horizons were proposed for urban soils: urbic (UR), filled compost-mineral (RAT), and filled peat (RT). The combination of these horizons with other diagnostic horizons and layers of technogenic materials correspond to different soil types. At the subtype level, the diagnostic properties (qualifiers) that may reflect both natural phenomena (gley, alkalinity) and technogenic impacts on the soils (urbistratified; phosphatic; or poorly expressed urban—ur, rat, rt) are used. Some corrections were proposed for the system of parent materials in urban environments. Urban soils formerly described in another nomenclature—urbanozems, urbiquasizems, and culturozems—are correlated with the taxa in all the trunks of the system. The proposals accepted can be used for the next updated version of the new Russian soil classification system.     

Amelioration strategies for saline soils: a review

Soil salinization is one of the major causes of declining agricultural productivity in many arid and semiarid regions of the world. Excessive salt concentrations in soils, in most cases, cannot be reduced with time by routine irrigation and crop management practices. Such situations demand soil amelioration. Various means used to ameliorate saline soils include: (a) movement of excess soluble salts from upper to lower soil depths via leaching, which may be accomplished by continuous ponding, intermittent ponding, or sprinkling; (b) surface flushing of salts from soils that contain salt crusts at the surface, a shallow watertable, or a highly impermeable profile; (c) biological reduction of salts by harvest of high‐salt accumulating aerial plant parts, in areas with negligible irrigation water or rainfall available for leaching; and (d) amelioration of saline soils under cropping and leaching. Among these methods, cropping in conjunction with leaching has been found as the most successful and sustainable way to ameliorate saline soils. Cropping during leaching or between leachings causes an increase in salt‐leaching efficiency because a decrease in soil water content occurs under unsaturated water flow conditions with a concurrent decrease in large pore bypass and drainage volume. Consequently, anaerobic conditions in soil may occur during leaching that can affect crop growth. Thus, in addition to the existing salt‐tolerant crop genotypes, research is needed to seek out or develop genotypes with increased tolerances to salinity and hypoxia. Since salt leaching is interacted by many factors, evaluation of the traditional concepts such as the leaching requirement (LR), the leaching fraction (LF) and the salt balance index (SBI) demands incorporation of a rapid, efficient and economical way of monitoring changes in soil salinity during amelioration. Besides this, numerous models that have been developed for simulating movement and reactions of salts in soils need evaluation under actual field conditions. Copyright © 2000 John Wiley & Sons, Ltd.     

The leaching of salts from restructured saline clay soils

Abstract. The leaching of salt from a restructured saline heavy montmorillonite clay soil was studied experimentally. Restructured clay was placed in a 25-m long ± 0.75-m deep polythene-lined trench and leaching studied under flood irrigation. The hydraulic conductivity of the soil always exceeded 25 m d^-1 during the experiment, and 85 % of the salt was leached within 16 days, most being leached in the first 8 days. The results indicate that restructuring clay could make the drainage of heavy clay soils economically feasible.     

Changes in the biological activity of heavy metal- and oil-polluted soils in urban recreation territories

Urban recreation areas of different sizes were investigated in the city of Vladimir. The degree of their contamination with heavy metals and oil products was revealed. The content of heavy metals exceeded their maximum permissible concentrations by more than 2.5 times. The total content of heavy metals decreased in the sequence: Zn > Pb > Co > Mn > Cr > Ni. The mass fraction of oil products in the studied soils varied within the range of 0.016–0.28 mg/g. The reaction of soils in public gardens and a boulevard was neutral or close to neutral; in some soil samples, it was weakly alkaline. The top layer of all the soils significantly differed from the lower one by the higher alkalinity promoting the deposition of heavy metals there. As the content of Ni, Co, and Mn increased and exceeded the background concentrations, but did not reach the three-fold value of the maximum permissible concentrations, the activity of catalase was intensified. The stimulating effect of nickel on the catalase activity was mostly pronounced at the neutral soil reaction. The urease activity increased when heavy metals and oil products were present together in the concentrations above the background ones, but not higher than the three-fold maximal permissible concentrations for heavy metals and 0.3 mg/g for the content of oil products. The nitrifying activity was inhibited by oil hydrocarbons that were recorded in the soils in different amounts.     

Urease activity in two cultivated and non-cultivated arid soils

Summary Since urease activity in soil is believed to be relatively constant, the present study was designed to examine the effects of incubation, soil depth and the effect of cultivation on the persistence of urease activity in arid soils. Two soils were used, a Harkey (coarse, silty, mixed, calcareous, thermic, Typic Torrifluvent) and a Saneli (Clayey over sandy skeletal, montmorillonitic, calcareous, Vertic Torrifluvent), each consisting of a cultivated field and a non-cultivated roadbed site. Urease activity was much lower and more varable in the roadbed soils (40 years without cultivation) than in the cultivated field soils. Pre-incubation for 24 h with urea (with toluene) and without urea (without toluene) greatly reduced the total urease activity in all cases in relation to cell free urease activity (with toluene). Urease activity in the two field soils decreased slightly with profile depth but the decrease was greatest below the plow depth (33 cm). Protease activity or some inactivation processes must have lowered the urease content since there was substantially reduced urease activity after most pre-incubations. The extent of the urease activity decrease was so great that the addition of urea would have been required to increase the production of urease enzyme.     

Restoration of saline land by halophytes for Indian soils

Usually saline soils were reclamized by chemical or mechanical remediation, since the cost of leaching technique for saline soil reclamation is higher in India. In the present study an attempt has been made to investigate to identify the fast and luxuriantly growing halophytic herbs which are salt accumulators and to assess the feasibility of salt bioaccumulation. From the results it is concluded that among six species studied Suaeda maritima and Sesuvium portulacastrum exhibited greater accumulation of salts in their tissues as well as higher reduction of salts in the soil medium.     

干旱区盐渍土介电常数特性研究与模型验证

常用的土壤介电模型一般都是针对非盐渍化土壤提出来的,对于干旱区盐渍化土壤,模型对于介电常数虚部的描述与实际测量情况有一定差距。为了更好地深入研究干旱区盐渍化土壤介电常数特性,该文选择盐渍土介电模型（修正的含水含盐土壤Dobson介电模型）作为典型研究区盐渍化土壤介电常数的基础模型,模拟分析土壤介电常数对模型参数的响应,在野外实测数据的支持下验证了盐渍土介电模型的适用性。研究结果表明：1）在低频区域（0.5＜f＜5 GHz）土壤介电常数对土壤体积含水量、含盐量的响应十分明显;2）土壤介电常数实部对土壤体积含水量的响应非常显著,线性拟合方程的相关系数R高于0.95,土壤含水量的大小直接决定着土壤介电常数实部的高低;3）土壤介电常数虚部对土壤含盐量的响应明显,线性拟合方程的相关系数R在0.86左右,可以认为土壤含盐量决定着土壤介电常数虚部的高低。研究证明利用土壤介电常数监测土壤含盐量、含水量和土壤盐渍化程度具有一定的潜力,通过盐渍土介电模型反演土壤含盐量是可行的。     

The effect of perennial herbs on the physical properties of saline soils

It is shown that the physical and water-physical properties of saline chernozemic-meadow soils improve under the impact of artificially sown perennial herbs: the content of water-stable aggregates >0.25 mm increases, the bulk density of the topsoil decreases, and the soil permeability increases. As the grass cover becomes older, the soil permeability somewhat decreases, though it remains higher in comparison with the soil without the plant cover. The effect of annual crops on the physical properties of the soils is less pronounced. The improvement of soil physical properties under perennial grasses favors the desalinization of the soil profile due to the migration of salts into the groundwater via root paths. Lucerne (Medicago sp.) and sweet clover (Melilotus suaveolens) with deep, well developed root systems have the most pronounced effect on the soil desalinization. A somewhat slighter ameliorative effect is typical of Elymus junceus.     

On the determination of total heavy metal content in saline soils and soils rich in organic matter

Abstract

Methods of soil decomposition for determination of heavy metal total content were considered. Two saline soils (chloride and sulphate solonchak solonetz) and one rich in organic matter were uzed for investigation. It has been established that decomposition by using HF‐HCl with a preliminary ignition at 500°C is a very suitable method. The type of the studied soils and the results obtained allow for this method to be recommended for decomposition of various soils.

On the basis of experiments with modelled soils it has been proved that possibilities for heavy metal losses on ignition are created when NaCl content and the percentage of weakly bound heavy metals (water‐soluble, exchangeable, etc.) are high. Under the conditions of the experiment (acid soils ‐ pH 4.3 and 5.0) losses of Zn and Pb but not of Cu have been incurred. Although these cases are not typical, this requires the applicability of the method for such particular occasions to be checked.     

Functional diversity of microbial communities in saline soils of the semidesert zone

The health status of microbial communities in soils of the Sulak Lowland (Dagestan) was estimated on the basis of data on their functional diversity. The health status of the microbial communities decreased in the following soil sequence: typical meadow soil > meadow-chestnut soil > dark chestnut soil > saline soil (solonchak). The low concentration of soluble salts (<1 meq/100 g of soil) had a positive effect on the functioning of the microbial communities. The health status of the microbial communities also depended on the soil humus content and pH conditions.