Zinc adsorption characteristics of selected calcareous soils of Iran and their relationship with soil properties

Abstract

The apparent recovery of applied zinc (Zn) by plants is very low in calcareous soils of Iran because most of it is retained by the soil solids. Subsamples of 24 surface soil (clay 130–530 g kg^‐1; pH 7.7–8.4; electrical conductivity 0.63–3.10 dS m^‐1; organic matter 6.0–22.0 g kg^‐1; cation exchange capacity 8–20 cmol kg^‐1; calcium carbonate (CaCO₃) equivalent 180–460 g kg^‐1) representing 13 soil series in three taxonomic orders were equilibrated with zinc sulphate (ZnSO₄) solutions and the amount of Zn disappeared from solution after a 24‐h shaking period was taken as that adsorbed (retained) by the soil solids. The adsorption data were fitted to Freundlich (X=AC^B) and Langmuir [X=(K‐bC)/(1+K#lbC)] adsorption isotherms. Backward stepwiseprocedure was used to obtain regression equations with isotherms coefficients as dependent and soil properties as independent variables. Freundlich A and Langmuir K were found to be highly significantly related to pH and clay and increasing as these soil properties increased. But Langmuir b was related only to clay and Freundlich B showed no significant relationship with any of the properties studied. The distribution coefficient (also called maximum buffering capacity), calculated as the product of Langmuir K and b, was also found to be highly significantly related to pH and clay. It is concluded that pH and clay content of calcareous soils are the most influential soil properties in retention of Zn.     

Optimum conditions for extraction of Al,Fe, and Si from soils with acid oxalate

Abstract

Acid oxalate reagent was used at various concentrations, pH values, shaking times, and soil to solution ratios to find the optimum conditions for the extraction of Al, Fe, and Si from short‐range‐order materials in soils and stream‐bed deposits. The optimum conditions vary with the nature of the soil sample and its components. For most soils maximum amounts of Al, Fe, and Si were extracted with 0.15M acid oxalate reagent at pH 3.0 with a soil to solution ratio of 1:100 and shaking for 4 h in the dark at 20°C. Soils with more than 5% oxalate‐extractable Al or Fe require a 0.20M oxalate solution at pH 3.0 with a soil to solution ratio of 1:200.

Allophane is extracted by acid oxalate reagent after shaking for 2 h and it may be estimated from the 4 h oxalate‐extractable Si values. Ferrihydrite is extracted after shaking for 4 h, and it may be estimated from the oxalate‐extractable Fe values. Either sodium oxalate or ammonium oxalate may be used     

A comparison of acid hydrolyses for the determination of carbohydrate content in soils

Abstract

Four Italian surface soils were used to compare four different acid hydrolyses for the determination of the total content of carbohydrates in soils. Soil hydrolyses in 0.25M and 1M H₂SO₄ and by mechanical shaking for 16 h released carbohydrates as efficiently as the 8 h soil hydrolysis under reflux. Degradation of released carbohydrates was probably the cause of the low values given by the hydrolysis in 72% H₂SO₄ for 15 min followed by a 16 h shaking in 0.5M H₂SO₄. This study confirms that the carbohydrate determination based on the colorimetric phenol‐sulphuric acid method is more accurate than the colorimetric anthrone‐sulphuric acid method. Moreover, soil characteristics may influence the accuracy and precision of results depending on the hydrolysis procedure as it was shown by the soils rich in organic carbon and clay.     

Factors affecting potassium fixation in calcareous soils of southern Iran

Potassium fixation capacity and mineralogical analysis of 24 representative soils, collected from southern Iran, were studied. Potassium fixation analysis was performed by adding six rates of K from 0 to 1000 mg kg^?1 soil in a plastic beaker and shaking for 24 h. Mineralogical analysis showed that the clay fractions were dominated by smectite, chlorite, mica, palygorskite, vermiculite and quartz. In general, the studied soils fixed 8.5–55% of the added K. The potassium fixation capacity of the studied soils was significantly correlated with smectite content (r ² = 0.87), clay content (r ² = 0.60), cation-exchange capacity (r ² = 0.79) and NH₄OAc-K. Wetting and drying treatment and incubation time had significant effects on K fixation. The average percentage increase in K fixation following the wetting and drying treatment was 24 and 30% for surface and subsurface soils, respectively. The average percentage increase in K fixation with increasing residence time was 79 and 56% for surface and subsurface soils, respectively. Because K fixation is a diffusion process, time and increased concentration of soluble K (because of soil drying) are factors affecting the rate of K diffusion from a soil solution to the interlayer positions of the expansible 2:1 clay minerals.     

Simultaneous fluometuron and norflurazon analysis in soil extracts and leachates

Abstract

Rapid, methanol‐extraction techniques for fluometuron (N, N‐dimethyl‐N'‐[3‐(trifluoromethyl) phenyl] urea) and norflurazon (4‐chloro‐5‐(methylamino)‐2‐(3‐(trifluoromethyl)phenyl)‐3(2(H)‐pyridazinone) from fortified soils have been reported to attain >90% recoveries. Analytical methods involving chromatographic separation coupled with fluorescence detection have also been described. The objectives of this study were to describe an analytical method for the simultaneous detection of fluometuron and norflurazon using ultraviolet spectro‐scopy in soil leachates and extracts and to examine the influence of residence time on herbicide recovery from fortified soil. The analytical method requires a gradient HPLC system, a reverse‐phase C‐18 column, and ultraviolet spectroscopy at a wavelength of 240 nm. The method is characterized by high reproducibility (spike recovery and diluted sample results are generally within 10% of the expected herbicide concentrations), low limits of detection (less than 1 (μg/L in soil leachates and 20 μg/L in soil extracts, depending on organic carbon content), and an applicable concentration range of more than two orders of magnitude. The recovery of fluometuron and norflurazon from fortified soils was significantly influenced by equilibration time, loading rate, and soil type (assuming zero chemical degradation). Most significantly, as herbicide contact time with the soil increased, recovery decreased. Thus, herbicide recoveries determined in the laboratory may not provide a true measure of herbicide recoveries from field soils.     

Experimental Evaluation of Procedures to Quantify Carbohydrate Carbon in Some Calcareous Soils

Carbohydrates are an important component of soil organic matter, and a method is needed to quantify them, which would be efficient in terms of time and cost. Different extractants and methods were examined in this work for their efficiency to extract carbohydrate C from four calcareous soils. Four extractants (distilled water, 0.5 M potassium sulfate (K₂SO₄), and 0.25 and 0.5 M sulfuric acid (H₂SO₄)) and three incubation methods (shaking for 16 h, heating in an oven (85 °C) for 16 h, and heating in a water bath (85 °C) for 2.5 h) were compared. The results show that significantly more carbohydrate C was extracted from all four soils with oven and water bath heating of the soil–extractant suspensions than with shaking them at room temperature. The efficiency of the extractants decreased in this order: 0.5 M H₂SO₄ > 0.25 M H₂SO₄ > 0.5 M K₂SO₄. The combination of the heated–water bath incubation method with 0.5 M H₂SO₄ as extractant was the most efficient method.     

Methodologically controlled variations in laboratory and field pH measurements in waterlogged soils

We have tested the reliability and consistency of conventional pH measurements made on water‐soil mixtures with respect to sieving, drying, ratio of water to soil, and time of shaking prior to measurement. The focus is on a waterlogged soil where the preservation potential of archaeological artefacts is critical. But the study includes agricultural and forest soils for comparison. At a waterlogged site, laboratory results were compared with three different field methods: calomel pH probes inserted in the soil from pits, pH measurements of soil solution extracted from the soil, and pH profiles using a solid‐state pH electrode pushed into the soil from the surface. Comparisons between in situ and laboratory methods revealed differences of more than 1 pH unit. The content of dissolved ions in soil solution and field observations of O₂ and CO₂ concentrations were used in the speciation model PHREEQE in order to predict gas exchange processes. Changes in pH in soil solution following equilibrium in the laboratory could be explained mainly by CO₂ degassing. Only soil pH measured in situ using either calomel or solid‐state probes inserted directly into the soil was not affected by gas exchange processes. Variations on the order of 0.2–0.5 pH unit in different laboratory methods could not be explained by degassing and seem to be soil‐type specific and strongly influenced by drying and shaking. Further attention should be given to standardization of pH measurements, particularly before pH measurements from different soil types are compared.     

Experimental evaluation of methods to quantify dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) in soil

A significant proportion of the total nutrient in soil solution can be bound to organic molecules and these often constitute a major loss from soil to freshwater. Our purpose was to determine whether chemical extractants used for measuring inorganic N could also be used to quantify dissolved organic nitrogen (DON) and carbon (DOC) in soil. In a range of soils, DOC and DON were extracted with either distilled water or 2 M KCl and the amount recovered compared with that present in soil solution recovered by centrifugal-drainage. The recovery of DON and DOC from soil was highly dependent upon the method of extraction. Factors such as soil sampling strategy (number of samples over space and time), sample preparation (sieving and drying), soil storage, extraction temperature, shaking time, and soil-to-extractant volume ratio all significantly affected the amount of DOC and DON extracted from soil. To allow direct comparison between independent studies we therefore propose the introduction of a standardized extraction procedure: Replicate samples of unsieved, field-moist soil extracted as soon as possible after collection with distilled water, 0.5 M K₂SO₄ or 2 M KCl at a 1:5 w/v ratio for 1 h at 20 °C.     

Amino acid interference with ammonium determination in soil extracts using the automated indophenol method

Abstract

The formation of a colored indophenol complex is commonly used as a quantitative measure of the ammonium content of soil extracts. The potential interference with ammonium determination from co‐extracted amino acids was examined. The extent of color development was examined for 22 amino acids by subjecting pure solutions to ammonium determination by both the indophenol method and steam distillation. Apparent detection of amino acid as ammonium ranged from 0 to 94 % of total nitrogen for the indophenol procedure, whereas steam distillation resulted in little apparent ammonium recovery. With the exception of threonine, the extent of color development was inversely related to amino acid molecular weight. The range in recoveries for the indophenol procedure suggests both size and composition of the co‐extracted amino acid pool is important in determining the extent of interference.

Significantly (p=0.001) greater estimates, averaging 0.4 μg mL^‐1, were found in indophenol estimates of mineral‐N content of moist, fresh soil samples. Air drying, oven drying or chloroform fumigation significantly increased the difference (0.3 ‐ 0.7 μg mL^‐1) in estimates of ammonium content. At 10: 1 extract: soil ratios this could cause ? to be overestimated by 3–7 μg g^‐1soil. The increased interference was attributed to a release of amino acid as a result of pretreatment. The difference between distillation and indophenol estimates of ammonium content of 0.5 M K₂SO₄was found to be dependent upon ammonium content. The use of procedures employing a distillation step (manual or automated) is recommended to avoid amino acid interference when precise NH₄+‐N determinations are needed on dried or fumigated samples.     

Interference by magnesium in the determination of nitrate in 2 M KCl extracts of soil by steam distillation

Abstract

Steam distillation of 2 M KCl extracts of soil showed low recovery of NO₃‐N when compared with an automated method for NO₃‐N determination. The low recoveries were more pronounced in extracts where a soil:solution ratio of 1:2.5 had been used. In extracts where the Mg²⁺ content was in excess of 0.02 M Mg, recoveries of added NO₃‐N could be as low as 25%. Increasing the amount of Devarda's alloy or using a 1:10 soil:solution extraction ratio overcame the problem of low NO₃‐N recovery. Calcium salts did not interfere in the recovery of added NO₃‐N.     

Chloride interference in total nitrogen analysis by the Kjeldahl method

Abstract

Very low recovery of NH₄+‐N was observed in total N determination of (NH₄)₂SO₄ in KC1 solutions by a semimicro Kjeldahl method using permanganate and reduced iron to recover NO₃‐ and NO₂‐, whereas complete recovery was obtained in analysis of NH₄+‐N in water, and of NO₃ ^?‐N or NO₂ ^?‐N in either water or KC1 solutions. The loss of NH₄ ⁺‐N observed with KC1 was attributed to the formation of NCl₃ upon reaction of NH₄ ⁺ with Cl₂ generated during oxidation of Cl^? by MnO₄ ^?. This difficulty is avoided by using K₂SO₄ instead of KC1 for extraction of inorganic N from soil. Complete recovery was obtained by adding ¹⁵N‐labeled NH₄+, NO₃‐, or NO₂‐ to 0.5 M K₂SO₄ soil extracts, and total ¹⁵N analyses of the labeled extracts were in good agreement with values calculated from the additions of ¹⁵N and the total N contents of the soil extracts.     

Effects of coalbed methane‐produced water on sorghum‐sudangrass growth and soil chemical properties

Abstract

Production of methane gas from coal seams generates well water that is slightly to moderately saline. Since land application is a potential method of disposal for this water, a greenhouse study was conducted to evaluate plant response and changes in soil chemical properties resulting from irrigation with coalbed methane‐produced water. The soil was a Montevallo (Typic Dystrochrepts)‐Nauvoo (Typic Hapludults) association located in northern Alabama. Two irrigation methods used in the initial greenhouse test were 1) continuous, irrigation 24 h d^‐1 and 2) intermittent, irrigation for 12 h and off for 24 h. In a second greenhouse test, three irrigation methods were used: 1) continuous, irrigation for 24 h d^‐1, 2) intermittent, irrigation for 12 h and off for 48 h, and 3) irrigation to maintain field capacity, by daily additions of the respective irrigation water. The flow rate for continuous and intermittent irrigation treatments was 3.75 mm h^‐1. In each greenhouse test, 5 levels of salinity were generated by mixing well‐produced water with deionized water to give solutions containing 0, 10, 20, 40, and 100% well‐produced water (specific conductance (second greenhouse test) of 0.2, 1.4, 2.2, 4.4, and 9.3 dS m^‐1, respectively). Corresponding sodium adsorption ratios were 0.1, 27, 36, 55, and 81, respectively. Sorghum‐sudangrass [Sorghum bicolor (L.) Monech] was harvested for forage yields and chemical analysis at 14–30 days after initiation of irrigation treatments. Results from these preliminary short term, greenhouse studies show that coalbed methane produced water that is typical for Alabama (total dissolved solids ≤2000 mg L^‐1) can be applied to highly weathered soils. The results indicate that plant growth of summer annual grasses will be optimized if an irrigation system is used to apply produced water at a rate to maintain soil moisture at or near field capacity.     

Manganese retention by selected calcareous soils as related to soil properties

Abstract

Calcareous soils often need supplemental manganese (Mn) to support optimum plant growth, but some reports show that the apparent recovery of applied Mn is very low in such soils, i.e., nearly all of the applied Mn is retained in the soil. This experiment was conducted to find the relationship between the retained Mn and selected properties of calcareous soils. Eleven surface (0–20 cm) soil samples with pH ranging from 7.7 to 8.1 and calcium carbonate equivalent (CCE) ranging from 20 to 50% were used in the Mn adsorption study. Two‐gram subsamples of each soil were equilibrated with 20 mL of 0.01M CaCl₂ solutions initially containing 10 to 200 mg Mn L^‐1. The Mn that disappeared from solution (after 6 h shaking at 25°C) was considered as adsorbed (retained) Mn. The adsorption data showed a highly significant fit to Freundlich and also to the two‐surface Langmuir adsorption isotherms. The coefficients of both isotherms showed significant positive correlations with cation exchange capacity (CEC), organic matter (OM), and CCE of the soils indicating that OM and calcium carbonate are the sites of Mn retention in calcareous soils. Comparison of the adsorption data of this experiment with those of plant Mn uptake of the same soils (published earlier) shows that as the Langmuir second surface adsorption maxima (maximum retention capacity) of the soils increase the plant Mn concentration and uptake decrease.     

Determination of nitrogen by microdiffusion in mason Jars. I. inorganic nitrogen in soil extracts

Abstract

Simple microdiffusion methods are described for determination of NH₄ ⁺, NO₃ ^‐, and NO₂ ^‐ in soil extracts. These methods involve diffusion of NH₃ in a 473‐mL (1‐pint) wide‐mouth Mason jar, the diffused NH₃‐N being collected in 3 mL of boric acid‐indicator solution in a 60 mm (dia.) Petri dish suspended from the Mason jar lid, for quantitative determination by titrimetry (0.0025 M H₂SO₄). Magnesium oxide is used to liberate NH₄ ⁺; Devarda's alloy is used to reduce NO₃‐ and NO₂ ^‐ to NH₄ ⁺; and sulfamic acid is used to eliminate NO₂ ^‐. Depending upon the volume of soil extract (10–50 mL), diffusion at room temperature (a20°C) was complete in 18–72 h with orbital shaking, and in 24–86 h without shaking. The methods gave quantitative recovery of NH₄ ⁺, NO₃ ^‐, and NO₂ ^‐added to soil extracts. A potential source of interference in the methods involving use of Devarda's alloy is the liberation of NH₄ ⁺‐N from alkali‐labile organic‐N compounds.     

Comparison of analytical procedures for determination of soil sorption coefficients of some triazine herbicides

Abstract

The sorption behavior of three triazine herbicides: atrazine, metribuzin, and terbutryn was studied in two different soils. Three experimental procedures to determine the K_f values were assayed: the conventional batch equilibration method in which the sorbed concentration is calculated by difference from the change in solution concentration; an alternative mass balance equilibrium batch technique in which the solution and the sorbed phase concentration are measured directly; and the flow equilibration method in which a solution of known concentration was passed through a column of soil until the effluent reached the same concentration as the input solution. Four concentrations of each herbicide were selected and results were fitted to the linearized form of the Freundlich isotherm. Recovery of the herbicides was studied in soil and water samples using the same four concentrations employed in the sorption assays. Average recoveries ranged from 86 to 104% with standard deviations lower than 10%. The K_oc (mg^1–1/n kg^‐1 L^l/n) values obtained ranged from 43 to 87 for atrazine, 27 to 114 for metribuzin, and 355 to 505 for terbutryn. The exponents 1/n of the Freundlich adsorption isotherms were lower than unity, with only one exception, and varied from 0.72 to 0.86 for atrazine, 0.73 to 1.12 for metribuzin, and 0.76 to 0.99 for terbutryn. The solution method gave values of K_oc that were 1.25, 1.55, and 2.65 (average of both soils) times those of the mass balance method for terbutryn, atrazine and metribuzin, respectively. When adsorption was low, the mass balance calculation method is recommended if the batch equilibration method is used, since the solution method can produce a considerable overestimation of adsorption. The flow equilibration method produced similar values of adsorption than the mass balance batch equilibration method and it made the experimental procedure easier since pesticide solution concentration need not to be measured once the equilibration time has been determined to ensure that the equilibrium was reached.     

Evaluation of an anion‐exchange membrane for extracting plant available phosphorus in soils

Abstract

Anion‐exchange resins (AER) have been used to determine plant available phosphorus (P) since the fifties and their results have shown strong relationships with plant growth and P uptake irrespective of soil properties. However, this procedure is still not widely used by laboratories because of difficulties in handling resin beads under routine conditions. New kinds and different shapes of resins are being produced each with specific characteristics that must be evaluated before use in laboratory procedures. Thus the objective of this work was to evaluate an AER manufactured in membranes reinforced with a Modacrylic fabric. These anion‐exchange membrane (AEM) sheets are commercially available, making them suitable for soil testing. The membranes were cut in pieces (1.0×7.5 cm) identified as AEM‐strips. The AEM‐strips were soaked in 0.5M HCl for a few days and transferred, after being rinsed with deionized water (DI), to 0.5M NaHCO₃ to convert them to HCO₃ ^‐ form. The AEM‐strips and resin beads in nylon bags recovered 98.4 and 98.0% of the P content in an aqueous P solution, respectively. Three eluent solutions were evaluated with different shaking times. The 0.1M H₂SO₄ and 1.0M NaCl in 0.1M HCl were equally suitable for the molybdenum blue color development without any pH adjustment, while the pH of the 0.5M HCl was too low. The elution of P from the AEM‐strips was independent of time with a 15‐min shaking being adequate for removal of all P from the strips. A comparison of soil sample preparation demonstrated that it was not necessary to vigorously grind or sieve the soil to improve the repeatability of the results. The AEM‐strips were compared with other methods (Pi impregnated filter paper, Mehlich I and Bray 1) using 32 soils from Guatemala with widely varying physico‐chemical and mineralogical properties. Phosphorus extracted by the AEM and Pi procedures (similar principle) were highly correlated and gave similar results irrespective of soil type. The acid extraction (Mehlich I and Bray 1 methods) attacked soil components (apatites) resulting in higher and inconsistent amounts of P extracted which may not be available to plants; the correlation between these methods within soils of similar properties was good, but when all soils were considered together the relationship was not significant. This demonstrated that the acid extraction method for P is not suitable for soils containing apatites, while those based on a sink for P (AEM and Pi) can be applied irrespective of the type of soil.     

Effect of sample preparation,length of time,and sample size on quantification of total lipids from bovine liver

The objective was to evaluate the effect of sample preparation (pulverization under liquid nitrogen, homogenization, or sonication), time length of sonication (0-60 s), shaking in chloroform/methanol solvent (0, 2, 4, or 12 h), incubation in chloroform (0 or 12 h), and drying of extracted lipids at 50 degrees C (2, 4, 6, or 24 h), and sample size (50-250 mg) on quantification of total lipids from bovine liver. Pulverization under liquid nitrogen yielded the lowest recovery. Sonication was least time-consuming for sample preparation. Precise estimates and the greatest recovery were obtained with 30 s of sonication, at least 2 h of shaking in chloroform/methanol solvent, 12 h of incubation in chloroform, and at least 6 h of drying. Sample sizes of at least 150 mg gave precise estimates. The results demonstrate that sample preparation, time length of different steps of the extraction procedure, and sample size affect quantification of total lipid from bovine liver.     

Control of soil solution interferences in an automated nitrate method

Abstract

An AutoAnalyzer method for nitrate nitrogen based on hydrazine reduction followed by diazotization was re‐examined after certain soil solutions had given poor recoveries. Modifications to the reaction parameters, particularly in the reduction stage improved the recovery of nitrate as nitrite. Soluble organic compounds in the samples were more critical than inorganic salts, but the proposed method allowed tolerance of up to 30 mgl^‐1 total organic carbon. Concentrations of various inorganic ions in soil solutions and natural waters were usually below the limits shown to be critical for the improved method.     

雨强和坡度对红壤坡耕地地表径流及壤中流的影响

地表径流和壤中流是坡面重要水文过程,雨强和坡度是影响坡面地表径流和壤中流产流主要因素。为研究降雨强度和地表坡度对坡耕地地表径流和壤中流的影响,该文采用人工模拟降雨试验法,在长3.0 m、宽1.5 m、深0.5 m土槽,设计4个不同坡度(5°、10°、15°、20°)和3个不同雨强(30、60、90 mm/h)对红壤坡耕地地表径流及壤中流产流过程进行模拟试验。结果表明:1)壤中流开始产流时间滞后于地表径流,降雨强度从30到90 mm/h,地表径流、壤中流产流开始时间均随雨强增大而减小,壤中流比地表产流开始滞后时间随着雨强增大先增大后趋于稳定;2)地表径流强度随雨强增大而增大,壤中流初始径流强度随雨强增大而增大,不同雨强下壤中流径流峰值相近;3)地表径流和壤中流产流过程曲线有明显差异,地表径流产流过程线先增大后趋于稳定,壤中流产流过程线呈抛物线型即先增大后减小;4)从5°到20°,地表产流开始时间随坡度增大而减小,壤中流产流开始时间随坡度增大先减小后增大;5)从5°到20°,地表径流强度先增大后减小,10°为转折坡度,壤中流产流峰值随坡度增大而减小,并且随着坡度增大达到壤中流峰值时间不断减小。     

Zinc adsorption by sterilized and non‐sterilized soil in the presence of citrate and catechol

Abstract

The effect of organic ligands on zinc (Zn) adsorption in the rhizosphere may be influenced by microbial activity depleting the concentration of the ligand over time. Zinc adsorption by sterile and non‐sterile lateritic soil was measured by shaking the soils with Zn solutions at a soil‐liquid ratio of 1: 5 for five periods of time ranging from 17–480 h. The concentrations of Zn and the ligands were determined after the selected times. The speciation of Zn was then estimated.

Changes in Zn adsorption with time in the presence of organic ligands were due to changes in pH and Zn complexation associated with the addition and breakdown of the organic ligands and with the technique of sterilization. Zinc adsorption was higher in non‐sterile than in sterile soil. Adsorption in the presence of citrate was lower than in its absence except in non‐sterile soil after 72 h. The adsorption in the presence of catechol was similar to that in its absence.