Factors affecting the sorption and fixation of caesium in acid organic soil

Radioactive caesium deposited on upland Britain following the Chernobyl accident in 1986 remains available for uptake by plants, despite the potential of the contaminated soils to fix Cs. The minimum concentration of Cs⁺ required to cause Cs⁺ fixation is 0.60 to 0.75 mm , and this is unlikely to be reached in any contaminated upland soil. It is suggested that the fixation is caused by interlayer collapse of the illitic clay. The observed Cs⁺ fixation in lowland mineral soils and its absence from acidic upland soils is explained by the action of K⁺ ions, which can also induce interlayer collapse. Although Cs⁺ ions are unlikely to be fixed in acid organic soils, they can be strongly sorbed on any unoccupied Cs-specific sorption sites in the narrow parts of illitic wedge zones. A method for determining the number of such sites is described. For two of the soils studied the number of sites ranged between 8 × 10^?8 and 1 × 10^?5 mmol kg^?1; for two others there appeared to be no unoccupied Cs-specific sites. Although Cs⁺ ions sorbed on such sites do not exchange with other ions, they can be desorbed if the concentration of Cs⁺ in solution is decreased. Thus, radioactive Cs in such soils will remain available for plant uptake, unless interlayer collapse can be induced.     

Factors affecting phosphate sorption along a Mediterranean, dolomitic soil and vegetation chronosequence

Phosphate sorption by calcareous soils has been studied mainly on heavily fertilized agricultural soils and soils with calcite as the main carbonate mineral. We examined factors affecting phosphate adsorption in the soils of a semi-arid, mediterranean, dolomitic, soil and vegetation chrono-sequence in southeastern Spain. The youngest soils are highly eroded, Sandy Regosols (Typic Xerorthents) under gorse-scrubland vegetation. These have small P sorption capacities, large Mg-Ca carbonate contents but small amounts of Fe and Al oxides. Small total P (HNO₃/HClO₄ digestion) concentrations (30–130 μg P g^?1), of which up to 90% is Ca-bound (HCl-extractable), are typical of these young soils. P sorption markedly increased when Ca²⁺ was added to the solution. The fractionation of previously sorbed P indicates that the fate of most of this extra-sorbed P is the labile-P fraction sorbed on to (carbonate) surfaces and the apatite-like fraction (NaHCO₃-extractable and HCl-extractable fractions). At the other extreme, older more-intensively weathered, sandy-clay-loam rendzinas (Entic Haploxerolls), supporting dense mature garrigue, have a much greater P adsorption capacity and larger clay and Fe and Al oxide concentrations. They have more total P (ca 400 μg P g^?1), much of it in occluded form (residual fraction). These soils show no significant differences in P sorption whether or not CaCl₂ was used as a background electrolyte. Considering the overall variations within the chronosequence, dithionite extractable Fe and Al are the properties best correlated with P sorption. This support the general finding that crystalline Fe-oxides (e.g. goethite and haematite) appear to be the most important P-sorbing component for soils in the Mediterranean region, rather than amorphous Fe-oxides (e.g. ferrihydrite) as is reported for more mesic areas. Stepwise multiple regression and fractionation data, however, suggest that, provided the soil solution is rich in Ca²⁺, carbonate may also be a significant contributing factor to P sorption, especially in the youngest of these dolomitic soils.     

Factors affecting soil microbial community structure in tomato cropping systems

Soil and rhizosphere microbial communities in agroecosystems may be affected by soil, climate, plant species, and management. The management and environmental factors controlling microbial biomass and community structure were identified in a three-year field experiment. The experiment consisted of a tomato production agroecosystem with the following nine treatments: bare soil, black polyethylene mulch, white polyethylene mulch, vetch cover crop, vetch roots only, vetch shoots only, rye cover crop, rye roots only, and rye shoots only. The following hypotheses were tested: (1) Temperature and moisture differences between polyethylene-covered and cover-cropped treatments are partly responsible for treatment effects on soil microbial community composition, and (2) Different species of cover crops have unique root and shoot effects on soil microbial community composition. Microbial biomass and community composition were measured by phospholipid fatty acid analysis. Microbial biomass was increased by all cover crop treatments, including root only and shoot only. Cover cropping increased the absolute amount of all microbial groups, but Gram-positive bacteria decreased in proportion under cover crops. We attribute this decrease to increased readily available carbon under cover-cropped treatments, which favored other groups over Gram-positive bacteria. Higher soil temperatures under certain treatments also increased the proportion of Gram-positive bacteria. Vetch shoots increased the amount and proportion of Gram-negative bacteria, fungi, and arbuscular mycorrhizal fungi in the rhizosphere of tomato plants. The imposed treatments were much more significant than soil temperature, moisture, pH, and texture in controlling microbial biomass and community structure.     

滇黔桂地区土壤有机碳密度变异的影响因素研究

土壤有机碳是土壤肥力的重要指标之一,也是陆地碳库的主要部分。揭示影响土壤有机碳储量的主要因素,对合理地利用土壤资源,减少土壤温室气体的排放,增加土壤碳存储等方面都具有重要的意义。土壤有机碳储量受气候、植被、土壤属     

单室结构土壤微生物燃料电池发电性能的影响因子研究

There is limited information about the factors that affect the power generation of single-chamber microbial fuel cells （MFCs） using soil organic matter as a fuel source. We examined the effect of soil and water depths, and temperature on the performance of soil MFCs with anode being embedded in the flooded soil and cathode in the overlaying water. Results showed that the MFC with 5 cm deep soil and 3 cm overlaying water exhibited the highest open circuit voltage of 562 mV and a power density of 0.72 mW m-2. The ohmic resistance increased with more soil and water. The polarization resistance of cathode increased with more soil while that of anode increased with more water. During the 30 d operation, the cell voltage positively correlated with temperature and reached a maximum of 162 mV with a 500 ft external load. After the operation, the bacterial 16S rRNA gene from the soil and anode was sequenced. The bacteria in the soil were more diverse than those adhere to the anode where the bacteria were mainly affiliated to Eseherichia coli and Deltaproteobacteria. In summary, the two bacterial groups may generate electricity and the electrical properties were affected by temperature and the depth of soil and water.     

Factors affecting the amount of phosphate extracted from soil by anion exchange resin

In resin—solution systems at equilibrium, solution concentration of phosphate was proportional to the square of the phosphorus sorbed, and inversely proportional to the weight of resin and the volume of solution. The rate of approach to equilibrium was decreased by: enclosing the resin in mesh bags, by increasing the volume of solution, and by decreasing the vigour of shaking.In resin-solution-soil systems, the concentration of phosphate in the solution was important in determining the amount of phosphate extracted from the soil. Consequently, phosphorus extracted increased as volume of water and weight of resin increased, and decreased when the resin was enclosed in mesh bags. Even after long periods of shaking, when the concentration of phosphate in solution had reached low values, appreciable phosphate remained on the soil in equilibrium with this solution phosphate. Equations suggested that, if the solution concentration could be reduced to zero, phosphate sorbed by the resin would be proportional to the phosphorus added to the soil. However, at finite levels of addition of resin, the proportion of added phosphate sorbed by the resin increased as the level of addition of phosphate increased.     

污灌区土壤重金属累积影响因素研究

本文研究了大气沉降、化学肥料施用、污水灌溉3个外源因素对污灌区土壤中重金属Hg、Cd、Pb累积的影响,结果表明:污灌区大气干湿沉降和施肥输入土壤中3种重金属元素的数量顺序为Pb>Cd>Hg。污灌水中重金属Hg、Cd、Pb含量的高低与相对应的灌区土壤中重金属的累积量的多少基本一致,对土壤Cd累积影响最大的是污水灌溉,对土壤Hg累积影响最大的是大气沉降,污灌与大气沉降对土壤Pb累积影响作用相近,施肥对3种重金属元素累积影响最小。     

鄂西南烟区土壤供氮特性影响因素研究

采用田间高频次取样方法,以不种植烤烟和不施肥土壤为对照,结合试验年份湖北省恩施州宣恩县城的气象资料,研究了气候因子、栽培和施肥等措施对宣恩县椒园镇烤烟土壤供氮特性的影响。结果表明:土壤碱解氮含量随气温上升而增加、随降雨量增加而降低,但一般比降雨时间滞后5～10d;未覆膜条件下施肥可在短期内(45d左右)明显增加土壤碱解氮含量;有机无机配合施肥烟株对氮的吸收大于纯施化肥;在烟叶生长的后期,有机无机配合施肥土壤碱解氮含量与单施化肥相比有降低趋势,因此有机无机配合施肥是调控烤烟后期氮素营养的有效措施。各因素对土壤碱解氮含量影响大小的次序为:栽培施肥气候,作物吸收、地膜覆盖等栽培因素是影响土壤碱解氮含量的最主要因子之一。     

Effect of soil components on the surfactant-enhanced soil sorption of PAHs

Purpose  

The use of cationic surfactants was proposed to enhance the soil retention of hydrophobic organic contaminants (HOCs). However, due to the complexity of soil composition, the effect of cationic surfactants on the soil sorption of HOCs was limited to a qualitative understanding. To gain further insight into the mechanism of the surfactant and predict its efficiency, a comparative study on the HOCs sorption capacities of the surfactants sorbed on pure typical soil components was investigated.     

Chemical factors affecting selenite sorption by allophanic soils

The sorption of selenite by two allophanic soils containing high amounts of variable charge materials was studied. Selenite sorption exhibited a maximum near pH 4 and decreased, although not proportionally, with increasing pH. Only negligible amounts of selenite were sorbed above pH 7.In the two soils, the addition of selenite caused a release of sulphate (SO²⁻₄), silicate (Si) and hydroxyl ion (OH⁻) and an increase in cation (Na⁺) adsorption. No measurable amount of phosphate (P) was released. Increase in negative charge as measured by Na⁺ adsorption accounted for 48 and 18% of selenite sorbed (soils 1 and 2, respectively), the rest being accounted for by release of anions. The results presented here are consistent with the widely held view that selenite and phosphate are sorbed onto variable charge surfaces by a similar mechanism (ligand exchange).     

Characteristics of earthworm casts affecting herbicide sorption and movement

Various physical and chemical characteristics of earthworm casts collected from a laboratory incubation and a field experiment were examined in relation to their effect on the sorption and the movement of three ¹⁴C-labelled ionic herbicides: atrazine, 2,4-dichlorophenoxyacetic acid, and metsulforon methyl. The earthworm casts contained higher levels of fine fractions and total and soluble C. This is attributed to the grinding action of the earthworm gut and selective feeding on zones with higher organic matter and fine size fractions. The earthworm casts had a higher pH than the source soil, resulting in a higher number of surface negative charges. The earthworm casts sorbed higher amounts of herbicides than the source soil, mainly due to the increases in the amount of organic C and fine size fractions. The incrased sorption of herbicides by the casts resulted in decreased leaching.     

Dissolved organic matter enhances the sorption of atrazine by soil

The influence of dissolved organic matter (DOM) on the sorption of atrazine (2-chloro-4-ethylamino-6-isopylamino-1,3,5-triazine) by ten soils was investigated. Batch sorption isotherm techniques were used to evaluate the important physiochemical properties of soil determining the sorption of atrazine in the presence of DOM. The sorption of atrazine as a representative of nonionic organic contaminants (NOCs) by soil with and without DOM could be well described by the Linear and Freundlich models. The n values of the Freundlich model were generally near to 1, indicating that linear partitioning was the major mechanism of atrazine sorption by soil samples. The apparent distribution coefficient, value, for atrazine sorption in the presence of DOM initially increased and decreased thereafter as the DOM concentration increased in the equilibrium solution. DOM at relatively lower concentrations significantly enhanced the sorption of atrazine by soil, while it inhibited the atrazine sorption at higher concentrations. For all the soil samples, the maximum of was 1.1~3.1 times higher than its corresponding K _d value for the control (without DOM). The maximum enhancement of the distribution coefficient () in the presence of DOM was negatively correlated with the content of soil organic carbon (SOC) and positively correlated with the clay content. The critical concentration of DOM, below which DOM would enhance atrazine sorption, was negatively correlated with SOC. The influence of DOM on atrazine sorption could be approximately considered as the net effect of the cumulative sorption and association of atrazine with DOM in solution. Results of this study provide an insight into the retention and mobility of a NOC in the soil environment.     

Evaluation of phosphorus sorption by an allophanic soil

Solutions containing different P concentrations were equilibrated with samples of an allophanic soil from Navarra (Spain) to determine whether P sorption conformed qualitatively and quantitatively to the Langmuir, Freundlich and Sokolowska isotherms.Phosphorus sorption conformed to the Langmuir isotherm. When the sorption d data were plotted according to the conventional and Hofstee forms, two linear relationships were obtained. At the lower equilibrium P concentrations the K₁ parameter determined by regression analysis was higher than those corresponding to higher equilibrium P concentrations. The values obtained for K₁ and K₂ by the conventional and Hofstee equations were different. A procedure for evaluating the coefficients for higher equilibrium P concentrations was proposed. The K₁ and K₂ values so obtained allowed us to generate an experimental curve by addition of calculated adsorption data. This suggests that the curve-splitting technique is satisfactory.The sorption data also conformed to the Freundlich and Sokolowska equations, but in the latter it was necessary to evaluate two different sets of parameters.The same experimental data can be adjusted to the three different equations, in one case with only one set of constants and in the other two cases with two different sets of parameters, one for the lower P concentrations and the other for the higher ones. Besides, to fit the experimental data to the Langmuir and Sokolowska equations, it was necessary to split the isotherm into two regions and these two regions were different for the Langmuir and the Sokolowska equations. This suggests that the parameters do not have any chemical signification and that they are only “curve fitting”.A study of the effect of pH on the P sorption indicated that low pH notably increased the P sorption.The soil samples had very high phosphate sorption capacity probably due to the very large specific surface and reactivity of the allophane.     

Factors affecting oxidation rates of elemental sulphur in a soil under a ryegrass dominant sward

Field and laboratory experiments were used to determine the effects of two consecutive applications of elemental sulphur (S°) on the S° oxidation rates and numbers of thiobacilli in a soil under a ryegrass dominant sward. The S° in soil samples were extracted into chloroform and analysed by a high performance liquid chromatography procedure. The rate of S° oxidation in the field experiment, expressed as the time in days required to oxidise 70% of added S°, decreased with decreasing diameter of S° particles because of the larger surface area of fine S° particles available for oxidation. Oxidation rates of S° also increased when S° was reapplied in autumn and spring because of the presence of large numbers of thiobacilli remaining from the first S° application and the higher soil temperatures and moisture conditions. These field observations were confirmed in laboratory experiments. Scanning electron microscopy of the S° particles showed that most were irregularly shaped with uneven, perforated surfaces. Spherical particles occurred infrequently and had smooth surfaces.     

引起小麦倒伏的因子分析

田间调查和室内测试的结果表明 ,倒伏主要是由于品种、密度、氮肥力及其交互作用造成 .氮肥力过高是倒伏的基础 ,品种、密度、降雨是倒伏的诱因     

Microscopic observations of bacterial sorption in soil cores

 Bacterial cells may be immobilized in soil through adsorption to a variety of soil particles. These associations affect the interaction of native soil microbes with their nutrient sources and control at least in part the distribution of foreign bacteria entering the soil system. To observe the relationship between soil structure and adsorption of amended bacterial cells, a series of intact cores of Freehold fine sandy loam were inoculated with suspensions of Arthrobacter crystallopoietes cells at concentrations ranging from 10⁶ to 10⁸ cells per ml. The cells were cultivated in a glucose-based medium to induce spherical cell formation. Following inoculation, the soil cores were rinsed with sterile water (30–40 ml h^–1), flushed with thiazine red R to stain the bacterial cells, and then prepared for examination by common micromorphological techniques. The use of fluorescence, polarizing, and reflected light microscopy of soil thin sections, allowed direct, qualitative determinations of microbial distribution and associations with soil components. A. crystallopoietes cells were detected throughout the length of the soil columns. Soil pores did not appear to be clogged by the spherical A. crystallopoietes cells. Adsorption of amended bacteria was governed by the presence of both variably charged mineral oxides and organic matter within the intergrain microaggregates and occurred along coated mineral surfaces. Amendment of non-inoculated soil columns with 0.2% (w/v) solution of glucose demonstrated that the staining and sectioning procedure was sufficiently sensitive to detect growth of indigenous bacterial populations and their distributions within the soil matrix. Received; 6 April 1997     

红壤基质组分对磷吸持指数的影响

在红壤旱地肥料长期定位试验(始于1988年)中,选取了无机肥试验区的NPK、NP、NK、PK,有机无机配施试验区的CK、CK+猪厩肥(BM)及CK+花生秸秆(SR)等7个施肥处理土壤,测定了土壤磷吸持指数(Phosphate sorption index,PSI),分析了PSI与红壤最大吸磷量(Xm)的相关关系,讨论了土壤pH、有机质、黏粒、铁铝氧化物及无机磷酸盐等基质组分对PSI的影响。结果表明:长期施磷或配施有机肥均可显著降低红壤PSI值,随着土壤pH的升高、有机质及铁结合态磷酸盐(Fe-P)含量的增加,红壤PSI显著降低;土壤游离铁铝氧化物及黏粒含量越高,PSI也越大。PSI与Xm呈显著线性相关关系(Xm=0.5PSI+412.8,n=15,r=0.967**,p<0.01),因此,可以用PSI替代Xm来表征土壤固磷能力,亦可由PSI的大小来推断土壤磷的供磷能力。     

Stabilization of dissolved organic matter by sorption to the mineral soil

The main process by which dissolved organic matter (DOM) is retained in forest soils is likely to be sorption in the mineral horizons that adds to stabilized organic matter (OM) pools. The objectives of this study were to determine the extent of degradation of sorbed OM and to investigate changes in its composition during degradation. DOM of different origins was sorbed to a subsoil and incubated for 1 year. We quantified mineralized C by frequent CO₂ measurements in the headspace of the incubation vessels and calculated mean residence times by a double exponential model. Mineralization of C of the corresponding DOM in solution was used as a control to estimate the extent of DOM stabilization by sorption. Changes in the composition of sorbed OM during the incubation were studied by spectroscopic (UV, fluorescence) and isotope (¹³C, ¹⁴C) measurements after hot-water extraction of OM.The fraction of sorbed organic C mineralized during the incubation was only one-third to one-sixth of that mineralized in solution. The mean residence time of the most stable OM sample was estimated to increase from 28 years in solution to 91 years after sorption. For highly degradable DOM samples, the portion of stable C calculated by a double exponential model nearly doubled upon sorption. With less degradable DOM the stability increased by only 20% after sorption. Therefore, the increase in stability due to sorption is large for labile DOM high in carbohydrates and relatively small for stable DOM high in aromatic and complex molecules. Nevertheless, in terms of stability the rank order of OM types after sorption was the same as in solution. Furthermore, the extent of sorption of recalcitrant compounds was much larger than sorption of labile compounds. Thus, sorptive stabilization of this stable DOM sample was four times larger than for the labile ones. We conclude that stabilization of OM by sorption depends on the intrinsic stability of organic compounds sorbed. We propose that the main stabilization processes are selective sorption of intrinsically stable compounds and strong chemical bonds to the mineral soil and/or a physical inaccessibility of OM to microorganisms. The UV, fluorescence and ¹³C measurements indicated that aromatic and complex compounds, probably derived from lignin, were preferentially stabilized by sorption of DOM. The ¹³C and ¹⁴C data showed that degradation of the indigenous OM in the mineral soil decreased after sorption of DOM. We estimated DOM sorption stabilizes about 24 Mg C ha⁻¹ highlighting the importance of sorption for accumulation and preservation of OM in soil.     

Factors affecting the cropping potential of reinstated soils

Abstract. Comparisons of crop production on recently reinstated soil in Northumberland have shown that the reduced yield potential of such soil may not be inevitable. Storage of soil in bunds did not greatly reduce subsequent crop yields, but failure to drain the land did. Provided an effective drainage scheme was installed, arable and grass crops could be grown successfully, responding very well to additions of nitrogen fertilizer and other normal good husbandry practices. To date it seems that neither deep cultivation nor the use of grass leys were as effective in the restoration process as had been expected.