Alkalinity of virgin solonetzes in northern Kalmykia (the Arshan-Zel’men Experimental Station)

The alkalinity of virgin solonetzes of the Ergeni Upland, Ergeni Plain, and Sarpinsk Lowland has been studied. These soils are characterized by the neutral salinization and the high alkalinity of the solonetzic and subsolonetzic horizons. The analysis of the soil water extracts demonstrated that the highest alkalinity is typical of the subsolonetzic horizons containing calcium carbonates (the B2 and BCca horizons). In the solonetzic horizons without CaCO₃, the alkalinity is lower despite the high exchangeable sodium percentage (up to 42%). The alkalinity of the solonetzic and subsolonetzic horizons may be conditioned by two processes: (a) the hydrolysis of the exchange complex (EC) containing sodium (EC-Na + H₂O ↔ EC-H + Na⁺ + OH⁻) and (b) the reaction of the ion exchange with the substitution of calcium for sodium in the exchange complex (EC-2Na + CaCO₃ ↔ EC-Ca + 2Na⁺ + CO₃²⁻). Calculations performed on the basis of the thermodynamic equations of the physicochemical equilibria according to the LIBRA program indicate that soda is absent in the solonetzic horizons, whose alkalinity is related to the carbonatecalcium equilibria. The high alkalinity of the calcareous subsolonetzic horizons is related to the presence of soda in combination with CaCO₃. The formation of soda in these horizons is due to the reaction of ion exchange described by Gedroits.     

La(NO3)3 对盐胁迫下黑麦草幼苗生长及抗逆生理特性的影响

为探讨稀土元素镧(La)对牧草盐胁迫伤害的缓解作用, 采用水培法研究了叶面喷施20 mg·L^-1La(NO₃)₃ 对NaCl 胁迫下黑麦草幼苗生长及其抗逆生理特性的影响。结果表明: 盐胁迫显著抑制黑麦草幼苗的生长, 提高叶片电解质渗漏率及丙二醛(MDA)、O₂^- 和H₂O₂ 含量, 其作用随盐浓度的增大而增强。超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX)活性和抗坏血酸(AsA)、谷胱甘肽(GSH)、可溶性蛋白质、脯氨酸含量随盐浓度增大呈先升后降趋势, 可溶性糖和Na⁺/K⁺比逐渐增大, 质膜H⁺-ATP 酶活性逐渐降低, 过氧化物酶(POD)活性及POD 同功酶数量表达增强。喷施La(NO₃)₃ 处理可降低盐胁迫下黑麦草幼苗叶片的O₂^- 和H₂O₂ 含量, 提高SOD、CAT、POD、APX 和质膜H⁺-ATP 酶的活性及POD 同功酶的表达, 使AsA、GSH、可溶性蛋白质、可溶性糖和游离脯氨酸含量及幼苗生物量增加, Na⁺/K⁺比降低。表明La(NO₃)₃ 可通过提高抗氧化系统的活性和积累渗透溶质减轻盐胁迫伤害, 从而提高黑麦草的耐盐性。     

Parameterization and regionalization of Cd sorption characteristics of sandy soils. II. Regionalization: Freundlich k estimates by pedotransfer functions

The aim was to describe Cd sorption in spatially variable sandy soils of the ‘Fuhrberger Feld’ catchment area as a prerequisite for prognosis of Cd transport in soil and of the threat of groundwater pollution. Thus, the possibility is evaluated to derive a generalized Freundlich equation based on multiple regressions relating the retention parameters k and M (from isotherm data of part 1 of this study) to basic soil properties (pedotransfer functions). For the parameter M (exponent), the correlation ‘measured vs estimated’ was weak (r² < 0.5) whereas k was well predictable by pedotransfer functions. The best regression was obtained if organic carbon (OC). clay content and H⁺ activity were combined as independent variables (r² up to 0.96). The obtained k values were much higher than those from comparable literature models, probably due to lower ionic strength and different composition of our background solutions used for the isotherms. As a critical evaluation, the estimates for k were used to derive solute Cd concentrations (C_est) which then were compared to measured data (range 0.1–3 μg L^?1). The best but still unsatisfactory r² was 0.77, obtained if G_est was compared to Cd in 0.01 M_c Ca(NO₃)₂ equilibria (Cd₀). Cd in fresh soil solution (Cd_z) showed no significant correlation with C_est, except for one relationship where OC had been excluded from the preceding multiple regression of k. Generally, the role of the variable OC remained unclear. Direct multiple regressions of measured solute Cd vs soil properties (bypassing k, no sorbed fraction) yielded much closer correlations, with r² = 0.9 for Cd₀ vs OC, H⁺ activity, clay (log data, OC decreases C) and r² = 0.7 for Cd₂ vs OC, H⁺ activity, clay (log data, OC enhances C).     

Effect of sodium chloride on CO2 evolution,ammonification, and nitrification in a Sassafras sandy loam

Sodium chloride, at rates up to 100 mg g^?1, was added to a Sassafras sandy loam amended with finely-ground alfalfa to determine the effect of NaCl on CO₂ evolution, ammonification, and nitrification in a 14-week study. A NaCl concentration of 0.25 mg g^?1 significantly reduced CO₂ evolution by 16% in unamended soil and 5% in alfalfa-amended soil. Increasing NaCl progressively reduced CO₂ evolution, with no CO₂ evolved from the soil receiving 100 mg NaCl g^?1. A 0.50 mg NaCl g^?1 rate was required before a significant reduction in decomposition of the alfalfa occurred. The NO^?₂-N + NO^?₃-N content of the soil was significantly reduced from 40 to 37 μg g^?1 at 0 and 0.25 mg NaCl g^?1, respectively in the unamended soil. In the alfalfa amended soil, nitrification was significantly reduced at 5 mg NaCl g^?1. At 10 mg NaCl g^?1, nitrification was completely inhibited, there being only 6 and 2 μg NO^?₂-N + NO^?₃-N g^?1 in the alfalfa amended and unamended soil, respectively. In the alfalfa amended soil NH⁺₄-N accumulated from 6 μg g^?1 at the 0 NaCl rate to a maximum of 54 μg g^?1 with 25 mg NaCl g^?1. These higher NH⁺₄-N values resulted in a 0.5 unit increase in the pHw over that of the 0 NaCl rate in the alfalfa amended soil. At NaCl concentrations above 25 mg g^?1 there was a reduction in NH⁺₄-N. The addition of alfalfa to the soil helped to alleviate the adverse affects of NaCl on CO₂ evolution and nitrification.     

Changes in chemical processes in soils caused by acid precipitation

In the absence of SO _infin4 ^sup= and NO _inf3 ^su? in precipitation, the pH of precipitation is primarily a function of CO₂?₂0 equilibria. Soil CO₂ and organic acids, acquired during descent through soil profiles, augment the dissolving capacity of the solutions which initially may have a pH of 4 or lower. The recent man-related increase of H₂SO₄ and HNO₃ in rainfall results in a significant lowering of pH in incident precipitation and an increase in corrosiveness of soil solutions. H₂SO₄ and HNO₃ may contribute some Eh buffering capacity. Particularly susceptible to these changes are clay minerals and redox sensitive elements such as Fe, Mn, Ni, and Co. The overall chemical weathering trends associated with increased acidity of rainfall will be de-stabilization and eventual solution of clay minerals (and the loss of their cation exchange capacity), increased rates of chemical denudation, and solution of illuvial Fe and Al oxides and hydroxides. The latter results in the loss of the adsorbed and coprecipitated metal trace elements associated with these highly reactive phases. The general result in soils developed on non-carbonate substrates is a tendency toward extensive podsolization, with associated decrease in clay minerals, loss of cation exchange capacity, and decrease in fertility.     

Chemical and biological relationships relevant to the effect of acid rainfall on the soil-plant system

This paper deals with problems concerning measurements of rainfall acidity and interpretation in terms of possible effects on the soil-plant system. The theory of acidity relationships of the carbon dioxide-bicarbonate equilibria and its effect on rainfall acidity measurements is given. The relationship of a cation-anion balance model of acidity in rainfall to plant nutrient uptake processes is discussed, along with the relationship of this model to a rainfall acidity model previously proposed in the literature. These considerations lead to the conclusion that average H+ concentration calculated from pH measurements is not a satisfactory method of determining H⁺ loading from rainfall if the rain is not consistently acid. Calculating loading from H⁺ minus HCO₃ ^? , strong acid anions minus basic cations, or net titratable acidity is suggested. The flux of H⁺ ions in soil systems due to plant uptake processes and sulfur and nitrogen cycling is considered. H⁺ is produced by oxidation of reduced sulfur and nitrogen compounds mineralized during decomposition of organic matter. Plant uptake processes may result in production of either H⁺ or OH^? ions. Fluxes of H⁺ from these processes are much greater than rainfall H⁺ inputs, complicating measurement and interpretation of rainfall effects. The soil acidifying potential due to the oxidation of the NH₄ ⁺ rainfall is examined, with the conclusion that acidity from this source is of a similar magnitude to direct H⁺ inputs common in rainfall.     

A comparison of measured and theoretical soil acidity diffusion coefficients over a wide range of pH

The soil acidity diffusion coefficients have been measured at two P_co2 levels with values in the range 2–70 × 10^?9 cm² s^?1. The coefficient passed through an ill-defined minimum in the pH range 5–6.5. Theoretical values, calculated on the basis that the only significant acid-base carriers in the soil were the H₃O⁺ -H₂O and H₂CO₃-HCO^?₃ pairs, agreed well with the experimental values over the whole pH range at P_co2= 0.005 atm. Agreement was not so good however at a CO₂ pressure of 0.0003 atm., especially in the neutralalkaline pH range. This was thought to be due to difficulties in maintaining this level of CO₂ throughout the soil samples.     

Effect of sodium chloride on denitrification in glucose amended soil treated with ammonium and nitrate nitrogen

Laboratory incubations were conducted to study the effect of sodium chloride (NaCl) on denitrification and respiratory gases (CO₂, O₂) from soil treated with ammonium or nitrate and incubated at 20 % moisture. The same samples were assayed for denitrifying enzyme activity (DEA) after incubation at 40 % moisture with glucose and NO₃^–. Under aerobic conditions (20 % water content), a flush of activity was observed at 6 hours after start of incubation and subsided to negligible levels at 12 hours. Sodium chloride significantly depressed N₂O and CO₂ emissions and O₂ consumption. Significantly more loss of N₂O occurred from NH₄⁺‐ than NO₃^–‐treated soil at all NaCl levels and was attributed to higher microbial activity. A highly significant positive correlation was obtained between N₂O emission and respiratory gases. The respiratory quotient (CO₂ evolved/O₂) was higher for NH₄⁺‐treated soil and decreased with the amount of NaCl. At 40 % moisture, N₂O emissions were higher than at 20 % and peaked at 37 hours followed by a sharp decrease. Short‐term incubations of soil with NH₄⁺ or NO₃^– did not have an effect on denitrifying enzyme activity (DEA) while NaCl had a positive effect, particularly in previously NO₃^–‐treated soil.     

Charge properties of mixtures of minerals with variable and constant surface charge

Surface charge of mixtures of lepidocrocite and illite determined by adsorption of potential-determining and electrolyte ions is studied as a function of pH and NaCl concentration. Deviations between results obtained by both methods were a function of the illite content of the mixtures, and can be mainly attributed to coatings of hydroxyaluminium complexes on the constant charge surfaces of the clay mineral, which can react with H⁺ ions or release exchange sites by precipitation of well-formed hydroxides. These coatings of aluminium complexes can cause H⁺ consumptions similar to those due to lepidocrocite. Some ideas are put forward for modelling charge properties of mixed systems.     

燕麦幼苗对氯化钠和氯化钾胁迫的生理响应差异

为探讨燕麦对NaCl和KCl胁迫的生理响应差异,采用水培法,研究了不同浓度NaCl和KCl胁迫对幼苗生长,活性氧代谢和渗透调节的影响。结果表明:(1)在75和150mmol/L浓度下,NaCl胁迫对燕麦幼苗的膜脂过氧化伤害和生长抑制大于KCl胁迫。NaCl胁迫下叶片中的超氧化物岐化酶(SOD),过氧化氢酶(CAT)活性及可溶性蛋白、可溶性糖和脯氨酸含量低于KCl胁迫;当浓度增大到225mmol/L时,KCl胁迫叶片中O-2.,H2O2,丙二醛(MDA),可溶性蛋白和可溶性糖含量显著大于NaCl胁迫,而SOD,抗坏血酸过氧化物酶(APX)活性及谷胱甘肽(GSH)含量则相反。(2)225mmol/L KCl和NaCl处理的植株叶片水势分别为-0.867和-1.034 MPa,渗透势分别为-1.409和-1.252 MPa,说明KCl对燕麦的更强伤害不是渗透胁迫所致;经225mmol/L KCl胁迫后,燕麦叶片中Na+含量下降至对照的36.5%,而K+含量上升为对照的1.49倍,而补充20mmol/L NaCl显著提高了225mmol/L KCl胁迫下叶片Na+的含量及SOD,APX活性,降低了K+,H2O2,O-2.和MDA含量,说明离子毒害引起的活性氧积累可能是高浓度KCl胁迫对燕麦幼苗伤害大于NaCl胁迫的重要原因。     

Solubility control of KCl extractable aluminum in soils with variable charge

Abstract

Solubility and kinetic data indicated that concentrations of aluminum (Al) extracted with 1 M KCl are determined by the solubility of a precipitated A1(OH)₃ phase in soils dominated by variable charge minerals. Kinetic studies examining the release of Al on non‐treated and KCl treated residues indicated the precipitation of an acid‐labile Al phase during the extraction procedure. The log ion activity products estimated for the KCl extracts ranged between 8.1–8.6 for the reaction Al(OH)₃ + 3H⁺ < = > Al³⁺+ 3H₂O, which was similar to the solubility product of several Al(OH)₃phases. The mechanism proposed for Al precipitation indicated that Al released by exchange with added K⁺ hydrolyzed and released H⁺ that was readily adsorbed on surfaces of variable charge minerals. The increased ionic strength of the extracting solution further increased the amount of H⁺adsorbed to the variable charge surface and reduced the H⁺ concentration in the aqueous phase. Consumption of H⁺ induced further hydrolysis of Al, resulting in supersaturation of the extracting solution and formation of polynuclear hydroxy Al species. It was concluded that the 1 M KCl extraction does not quantitatively extract salt exchangeable Al from variable‐charge soils.     

Interactions of allophane with humic acid and cations

Allophanic soils are known to accumulate organic matter, but the underlying mechanism is not well understood. Here we have investigated the sorption of humic acid (HA) by an allophanic clay in the presence of varied concentrations of either CaCl₂ or NaCl as background electrolytes. Both the HA and the clay were separated from New Zealand soils. Much more HA was sorbed in CaCl₂ than in NaCl of the same ionic strength. Apparently Ca²⁺ ions were more effective than Na⁺ ions in screening the negative charge on HA. In CaCl₂ the HA molecule might also assume a more compact configuration than in NaCl. In the presence of CaCl₂ sorption increased, reached a maximum, and then declined as the concentration of HA in solution was increased. This behaviour was not observed in NaCl where sorption showed a gradual and steady increase with HA concentration. We propose that ligand exchange occurs between the surface hydroxyl groups of allophane and the carboxylate groups of HA. As a result, the allophane–HA complex acquires negative charges, requiring the co‐sorption of extraneous cations (Ca²⁺ or Na⁺) for charge balance. The Ca²⁺ co‐sorbed can attract more HA to the complex possibly by a cation‐bridging mechanism, giving rise to a maximum in sorption. The decline in sorption beyond the maximum may be ascribed to a decrease in the concentration of free Ca²⁺ ions through binding to HA molecules in solution. The increase in supernatant pH may be attributed to a ligand exchange reaction between the surface hydroxyls of allophane and the carboxylate groups of HA, and proton binding to the allophane–HA complex.     

Sodium‐calcium interactions with growth,water, and photosynthetic parameters in salt‐treated beans

Calcium (Ca²⁺) amelioration of the plant's growth response to salinity depends on genetic factors. In this work, supplemental Ca²⁺ did not improve growth in Phaseolus vulgaris L. cv. Contender under high‐saline conditions and negatively affected several physiological parameters in nonsalinized plants. The response to supplemental Ca²⁺ was examined using plants grown in 25% modified Hoagland solution at different Na⁺ : Ca²⁺ ratios. In control plants (1 mM Ca²⁺; 1 mM Na⁺) surplus Ca²⁺ (4 or 10 mM) was associated with stomatal closure, decrease of hydraulic conductivity, sap flow, leaf specific dry weight, leaf K⁺ and leaf Mg²⁺ concentrations, and inhibition of CO₂ assimilation. Leaf water content was enhanced, while water‐use efficiency and dry matter were unaffected during the 15 d experimental period. The Ca²⁺ effect was not cation‐specific since similar results were found in plants supplied with high external Mg²⁺ or with a combination of Ca²⁺ and Mg²⁺. Relative to control plants, salinization (50 and 100 mM NaCl) caused a decrease in dry matter, hydraulic conductivity, sap flow, leaf Mg²⁺ activity, and inhibition of stomatal opening and CO₂ assimilation. However, NaCl (50 and 100 mM NaCl) enhanced leaf K⁺ concentration and water‐use efficiency. At 100 mM NaCl, leaf water content also significantly increased. Supplemental Ca²⁺ had no amelioration effect on the salt‐stress response of this bean cultivar. In contrast, the 50 mM–NaCl treatment improved stomatal conductance and CO₂‐assimilation rate in plants exposed to the highest Ca²⁺ concentration (10 mM). Phaseolus vulgaris is classified as a very NaCl‐sensitive species. The similarities in the effects caused by supplemental Ca²⁺, supplemental Mg²⁺, and NaCl salinity suggest that P. vulgaris cv. Contender has a high non‐ion‐specific salt sensitivity. On the other hand, the improvement in gas‐exchange parameters in Ca²⁺‐supplemented plants by high NaCl could be the result of specific Na⁺‐triggered responses, such as an increase in the concentration of K⁺ in the leaves.     

The effects of electrolyte concentrations on calcium-sodium exchange equilibria in two soil samples of india

The effects of total electrolyte concentrations of the equilibrium solutions (t.e.c.) on Ca²⁺-Na⁺ exchange equilibria in two soil samples (high and low in organic matter, clay content and CEC) were studied. Homoionic (Na⁺-saturated) soil samples were equilibrated with solutions having a large range in sodium adsorption ratio (SAR) at 25, 50, 75 and 100 meq. 1^-1 t.e.c. The exchange equilibria data were analysed, using a thermodynamic approach and the selectivity coefficients of Gapon (1933), Vanselow (1932) and Krishnamoorthy et al. (1948) (K_G, K_V and K_KDO). At a given proportion of Ca²⁺: Na⁺ in the equilibrium solution, the development of the exchangeable sodium percentage (ESP) in both soil samples increased with the increase in t.e.c. At a given SAR, the effect of t.e.c. on the development of ESP was less on a soil sample with high organic matter (O.M.), clay content and cation exchange capacity (CEC) than on a soil sample with low O.M., clay content and CEC. The values of exchange selectivity coefficients decreased with the increase in t.e.c, and did not remain constant throughout the exchange isotherm for any of the t.e.c. tried.     

Chemistry of the Urauchi River Water in Iriomote Island National Park, Okinawa, Japan

The chemical characteristics of the Urauchi River water in Iriomote Island National park, Okinawa, Japan have been studied. Concentrations of PO₄ ^3?, NO₂ ^?, and NH₄ ⁺ were barely detectable. We compared the concentration ratios of Mg²⁺/Na⁺, HCO₃ ^?/Na⁺, and Ca²⁺/Na⁺ in the Urauchi River to those of 60 large rivers in the world and indicated that the chemical composition of the river is most likely formed by the binary mixing of sea salt components and silicate rock weathering components. Although rock weathering in the catchments area is driven by both H₂CO₃ and H₂SO₄, the role of H₂CO₃ is dominant. The percentages of the concentration of each cation in the river water are almost the same as those of other rivers with drainage areas consisting of silicate rock and sandstone. Thus, the Urauchi River shows the typical chemical characteristics of a river in a silicate rock area that includes sandstone.     

GROWTH AND PHYSIOLOGICAL RESPONSE OF HYDROPONICALLY-GROWN SUNFLOWER AS AFFECTED BY SALINITY AND MAGNESIUM LEVELS

The effects of NaCl and magnesium levels (Mg²⁺) on the physiological response of sunflower were investigated. Plants were grown for 54 days in hydroponic culture with NaCl (100 mM) or without NaCl and four concentrations of Mg²⁺: 0, 0.4, 1.0 and 5.0 mM. At the end of the vegetative growing cycle of sunflower, salt stress reduced leaf area development by 51% and dry matter accumulation by 37% as compared to non saline-treated plants; at this stage, considering the percent reduction of partitioned plant dry matter, roots (42%) and leaves (35%) showed to be more salt-sensitive than stem. Growth reduction was related to the drop in net CO₂ assimilation rate and stomatal conductance, which started declining later during the vegetative growth period when leaf ion concentration started increasing. The investigated genotype was unable to exclude ions and significant amounts of Cl^? (about 1700 μmol g^?1 DW) and lesser Na⁺ (700 μmol g^?1 DW) accumulated in the leaves. The decline in net CO₂ assimilation was well correlated to the increase in leaf Cl^? concentration (r² = 0.71) and not to leaf Na⁺ concentration (r² = 0.33). The results suggest that, though sunflower develops an endogenous protection system by which it redistributes this ions in the whole plant, with more ions accumulating in roots and older leaves, growth reduction may be attributed to specific toxic effects of Cl^? on photosynthetic functionality. In both saline and non saline conditions, little or no significant differences in growth parameters of plants exposed to a range from 0.4 to 5 mM of Mg²⁺ were observed. Whereas, its deficiency caused a drastic reduction of dry matter accumulation up to 90%, due to progressive decline in CO₂ assimilation rate and chlorophyll content, with imbalances in Ca²⁺, Mg²⁺ and K⁺.     

Salts and acids as determinants of the solution composition of acidic forest soils — anion effects

The study aimed at evaluating whether salt-induced mobilization of acidity may be modified by the type of anion. For this purpose, the effects of different neutral salts on the solution composition of acid soils were investigated. The results were compared with those of the addition of acids. Two topsoil (E and A) and two subsoil horizons (Bs and Bw) were treated with NaCl, Na₂SO₄, MgCl₂, MgSO₄, HCl, and H₂SO₄ at concentrations ranging from 0 to 10 mmol dm^?3. With increasing inputs of Cl^? the pH of the equilibrium soil solution dropped, the concentrations of Al and Ca increased, and the molar Ca/(Al³⁺ + AlOH²⁺ + Al(OH)₂⁺) ratios decreased. These effects were the least pronounced when NaCl was added and the most at the HCl treatments. According to the release of acidity, the topsoils were more sensitive for salt-induced soil solution acidification whereas on base of the molar Ca/(Al³⁺ + AlOH²⁺ + Al(OH)₂⁺) ratios, the salt effect seems to be more important for the subsoils. Addition of S0₄^2? salts and H₂SO₄ induced higher pH and lower Al concentrations than the corresponding Cl^? treatments due to the SO₄^2? sorption, especially in the subsoils. The Ca/(Al³⁺ + AlOH²⁺ + Al(OH)₂⁺) ratios were higher than those of the corresponding Cl^? treatments. In subsoils even after H₂SO₄ additions these ratios were not higher than those of the NaCl treatments. The results indicate (I) that speculation about the effects of episodic salt concentrations enhancement on soil solution acidification not only need to consider the ionic strength and the cation type but also the anion type, (II) that salt-induced soil solution composition may be more crucial in subsoils than in topsoils, and (III) that in acid soils ongoing input of HNO₃ due to the precipitation load may induce an even more acidic soil solution than the inputs of H₂SO₄ of the last decade.     

H+‐atpase and H+‐transport activities in tonoplast vesicles from barley roots under salt stress and influence of calcium and abscisic acid 1

Seedlings of two barley cultivars differing in NaCl sensitivity were treated with low (100 mM) or high (400 mM) concentration of NaCl for 6 days. Tonoplast vesicles were prepared from roots, and H⁺‐ATPase and H⁺‐transport activities associated with tonoplast were assayed. Both H⁺‐ATPase and H⁺‐transport activities in the two cultivars were increased at 100 mM NaCl. These activities also increased in the salt‐tolerant cultivar at 400 mM NaCl, but in salt‐sensitive cultivar were decreased. In vivo treatment with 10 mM Ca²⁺ stimulated H⁺‐ATPase and H⁺‐transport activities at two levels of NaCl, however, treatment with 10⁵M (±) abscisic acid (ABA) inhibited these activities. From these results we propose that the increase of the vacuolar H⁺ pumps in barley roots reflects an adaptation to salt stress. The stimulation of HVATPase and H⁺‐transport activities by calcium (Ca) depends mainly on its effect in maintaining stability of membrane under salt stress.     

Evaluation of Extractants and Quantity–Intensity Relationship for Estimation of Available Potassium in Some Calcareous Soils of Western Iran

Accurate estimation of the available potassium (K⁺) supplied by calcareous soils in arid and semi‐arid regions is becoming more important. Exchangeable K⁺, determined by ammonium acetate (NH₄OAc), might not be the best predictor of the soil K⁺ available to crops in soils containing micaceous minerals. The effectiveness of different extraction methods for the prediction of K‐supplying capacities and quantity–intensity relationships was studied in 10 calcareous soils in western Iran. Total K⁺ uptake by wheat grown in the greenhouse was used to measure plant‐available soil K⁺. The following methods extracted increasingly higher average amounts of soil K⁺: 0.025 M H₂SO₄ (45 mg K⁺ kg^?1), 1 M NaCl (92 mg K⁺ kg^?1), 0.01 M CaCl₂ (104 mg K⁺ kg^?1), 0.1 M BaCl₂ (126 mg K⁺ kg^?1), and 1 M NH₄OAc (312 mg K⁺ kg^?1). Potassium extracted by 0.01 M CaCl₂, 1 M NaCl, 0.1 M BaCl₂, and 0.025 M H₂SO₄ showed higher correlation with K⁺ uptake by the crop (P < 0.01) than did NH₄OAc (P < 0.05), which is used to extract K⁺ in the soils of the studied area. There were significant correlations among exchangeable K⁺ adsorbed on the planar surfaces of soils (labile K⁺) and K⁺ plant uptake and K⁺ extracted by all extractants. It would appear that both 0.01 M CaCl₂ and 1 M NaCl extractants and labile K⁺ may provide the most useful prediction of K⁺ uptake by plants in these calcareous soils containing micaceous minerals.     

Interaction of clays with dilute fluoride solutions

Interaction between dilute (mg L^?1) NaF solutions and clay suspensions (0.08 % w/v) has been examined as a function of pH (range 3 to 8), clay type (Na⁺- or Ca²⁺-kaolinite, illite, montmorillonite) and NaF concentration. No F loss from solution was detected at pH > 6.5, while enhanced uptake was found on decreasing the pH, especially in the 4 to 3 region. Removal of F from 1 to 6 × 10^?4 M NaF was only slightly dependent on weight of solid, but did increase with [F^?]. It is proposed that F losses are due to the formation of sparingly soluble Al species (e.g. cryolite, Na fluoro silicate), occasionally augmented with CaF₂ formation (Ca²⁺-clays). The Al is released by proton attack on the lattice, following conversion of the suspended solids into the unstable H⁺-form, either through acid addition (pH < 5) or through hydrolysis of the Na⁺-form material. The latter process was most pronounced with the illite and montmorillonite samples. The amount of F fixed by montmorillonite was roughly double that held by the other two clays, and had a maximum value (pH 3) of ～ 4 mg g^?1, using 11 mg L^?1 NaF solutions. Soluble fluoro-complexes, similar in quantity to the retained F, were detected, in many of the studies. It was concluded that contact of the clay components of soils or sediments with mg L^?1 levels of F in adjacent aqueous phases would result in only a minor proportion being retained.