جستجوی مقالات مرتبط با کلیدواژه "پتاسیم غیر تبادلی" در نشریات گروه "آب و خاک"

Potassium is an essential element for plant growth and exists as four forms in soils: soluble, exchangeable, non-exchangeable, and mineral. Soluble and exchangeable K are considered as readily available and non-exchangeable K as slowly available. Organic matters and acids play an important role in increasing the bioavailability of nutrients especially potassium in the soils. Organic acids are low-molecular weight CHO containing compounds which are found in all organisms and which are characterized by the possession of one or more carboxyl groups. Depending on the dissociation properties and number of these carboxylic groups, organic acids can carry varying negative charge, thereby allowing the complexation of metal cations in solution and the displacement of anions from the soil matrix.The ability of an organic acid to release K from soils depends on some factors such as: diffusion rate of the organic acid in soil, the diffusion capability of organic acid-element complexes, the contact time of the organic acid on a mineral surface, the ionization of the organic acid, the functional group of the organic acid and its position, and the chemical affinity between the organic acid and the mineral elements. This study was conducted in order to evaluate the effect of organic acids and vermicompost on transformation of K in some selected soils of Fars Province, southern Iran.
In this study, nine soils with enough diversity were selected from different parts of Fars Province. The experiment was done as a completely randomized design with three replications, consisting of three incubation times (5, 15 and 60 days) and four organic compounds (including 2% vermicompost, three acids of citric, malic and oxalic acid eachat a concentration of 250 mmolkg-1and one control). The samples were incubated at 50% of saturation moisture at 22°C. Routine physicochemical analyses and clay mineralogy were performed on soil samples. Soil reaction, texture, electrical conductivity, calcium carbonate, and gypsum were identified. Soluble, exchangeable, non-exchangeable and mineral potassium were measured. The amounts of K forms in each sample were determined. Total K was determined following digestion of soil (110°C) with 48 % HF and 6 M HCl. Water soluble K was measured in the saturated extract. Exchangeable K was extracted with 20 ml 1.0 M NH4OAc (pH 7.0) for 5 min. Nitric acid-extractable K was measured by extraction of a soil sample with boiling 1.0 M HNO3 for 1 h. Potassium was measured on all filtrated extracts by flame photometer. The content of clay minerals was determined semi-quantitatively, using peak areas on the diffractograms of ethylene glycol solvated specimens. Statistical analysis was accomplished using the SPSS 16.0 software and the comparison of mean values was done using the Duncan test at the 5% level of significance.
The amount of different forms of K including water soluble, exchangeable, HNO3-extractable, and mineral K are relatively high in the studied soils. Mineralogical analysis indicated that smectite, illite, palygorskite and chlorite were the major minerals in the clay fractions. The results also showed that exchangeable, non-exchangeable and total potassium were in the range of 166 to 378, 282 to 1694, and 2312 to 8437 mg/kg-1, respectively.Organic acids and vermicompostwere led toa significant increase in soluble K at all times compared to control and vermicompost treatment exhibited greater effect. These treatments also significantly increased exchangeable potassium compared to control. Significant differences between exchangeable potassium of organic acids and vermicompost treatments were not observed at 5 and 15 days, but significant differences were observed between treatments of mallic and oxalic acids at 60 days. Compared to the control, the non exchancheable K showed significant increase in all three organic acid treatments and vermicompost at 15 and 60 days.
Based on the results, while exchangeable and non-exchangeable (NEK) potassium showed a clear trend in treatments, solution potassium was first increased and then showed a decreasing trend due to the rapid changes in liquid phase compared to the solid phase. All treatments significantly increased soluble potassium in each 3 times. The greatest potassium increase associated with vermicompost. In general, oxalic acid> malic acid>vermicompost> citric acid, were increased exchangeable potassium, while the trend for NEK was in the order of oxalic acid> malic acid> citric acid>vermicompost, respectively. All treatments at all times (except for treatment 5 days of NEK), showed a significant increase in the exchange and NEK potassium compared to the control. The results also reflect the effect of the dominant soil clay mineral on transformation of exchangeable and NEK, so that the highest and lowest rate of increase was related to the soils with dominant palygorskite and illite, respectively. In general, it seems that the use of organic acids and organic matter leads to a rapid increase of potassium, which must be properly managed in the soils with high leaching. Due to the complexity of soil environment in terms of soil physical, chemical and biological aspects and the role of these factors on potassium transformation, repeating of this experiment in other soils is recommended.

Potassium (K) as a macroelement is frequently made available by weathering of aluminosilicates such as K-feldspar and micaceous minerals in the soils. The objectives of this study were to determine the effect of mineral grain size and type of extractant on the different forms of K of micaceous and K-feldspar minerals and to find out a relationship between aqua-regia extractable K and type of K-bearing minerals. Water soluble, exchangeable, non-exchangeable and aqua-regia exteractable K of 50-100 and <50 μm sizes of biotite, phlogopite, muscovite, zanjan and yazd K-feldspars were investigated. The amount of released K was measured by flame photometer. The results indicated that the amounts of soluble and exchangeable K of trioctahedral micas (biotite and phlogopite) and feldspars are not greatly different, but in this regards, diotahedral muscovite is less important even than feldspars. Soil reservoir of non-exchangeable potassium is significantly higher in trioctahedral micas (up to 17 g kg-1) than muscovite and feldspars (up to 3 g kg-1). The small particles (<50 μm) had a significant effect on the different forms of K in all minerals. The amount of aqua-regia extractable K from trioctahedral micas exceed to 81 g kg-1. This value was 4 g kg-1 for other minerals. The mineral size had no effect on the aqua-regia extractable K in trioctahedral micas while in muscovite and feldspars this form of K increase up to 3.5 times with particle size reduction. More investigations are necessary to propose aqua-regia extractable K as an indicator for assessing type and amount of K-bearing minerals and soil potassium supplying power.

Kinetical study on non-exchangeable potassium (NEK) release is necessary for management, optimum use of soil resources, availability and supplying power of potassium. Information about NEK release rate in Golestan soils is limited. The aim of this study was to investigate the NEK release of saturated soil sample by calcium using acid citric and CaCl2 extractants from 2 to 1844 h duration in 12 dominant soil series in Golestan province. Different soils indicated various responses to continuous extraction. The rate of K released in different soils was lower in CaCl2 than that of Citric acid. Potassium release was faster in earlier periods of the extraction in all soils followed by a lower release rate. Due to high coefficient of determination and low value of the standard error of the estimate, the NEK release kinetic by citric acid and CaCl2 were well described by Elovich and Parabolic diffusion equations and Power, First order and Elovich equations, respectively. Therefore, NEK release rate was controlled by K diffusion from weathered surface of soil minerals.

Information about nonexchangeable potassium (NEK) release rate in Hamadan soils is limited. The objective of this study included an investigation of the dynamics of NEK in some soils from Hamadan Province by successive extraction with dilute citric acid over a period of 2500 h and determination of the correlation between the rate constants in this kinetic equation with soil properties. The results of this experiment showed that the initial NEK release rate was rapid which slowed down later on. The amount of NEK released after 2500 h ranged from 0.87 to 2.89 cmol kg-1. The amount of NEK released after 2500 h was significantly correlated with CEC, NEK, and soil separates. First order, parabolic diffusion law and power function equations described well the NEK release kinetics based on their highest determination coefficient and their lowest value of the standard error of the estimate. Release rate constant in the first order, parabolic diffusion law and power function equations ranged from 1.0×10-4 to 3.0×10-4, 1.7×10-4 to 10.6×10-4 and 2.75×10-1 to 4.6×10-1, respectively. In the correlation study the rate constants in the kinetic equations were correlated with some chemical properties and particle size distribution. The results of this experiment also showed that dilute citric acid can be used in the study of NEK release.