Niloofar Sadri; Hamidreza Owliaie; Ebrahim Adhami; Mahdi Najafi
Abstract
Introduction: 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 ...
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Introduction: 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.
Materials and Methods: 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.
Results and Discussion: 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.
Conclusion: 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.
N. Sadri; H.R. Owliaie; E. Adhami; M. Najafi Ghiri
Abstract
Introduction: The optimum and sustainable use of soil is only possible with a correct and complete understanding of its properties. Potassium (K+) is an essential element for plant growth and is a dynamic ion in the soil system and its importance in agriculture is well recognized. According to increasing ...
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Introduction: The optimum and sustainable use of soil is only possible with a correct and complete understanding of its properties. Potassium (K+) is an essential element for plant growth and is a dynamic ion in the soil system and its importance in agriculture is well recognized. According to increasing order of plant availability, soil K exists in four forms: mineral (5000-25000 ppm), nonexchangeable (50-750 ppm), exchangeable (40-600 ppm), and solution (1-10 ppm). K cycling or transformations among the K forms in soils are dynamic. The objectives of the present research were to study the relationship between different forms of potassium and clay mineralogy as well as soil evolution of 14 surface soil samples from some selected locations of Fars Province.
Materials and methods: Fars provinces, with an area of 122000 km2 located in southern Iran. The elevation varies from 500 m to 4400 m above mean sea level. Mean annual precipitation ranges from about 350 mm to 850 mm. Mean annual temperature ranges from 10°C to 24°C. According to Soil Moisture and Temperature Regime Map of Iran, the soils comprise xeric, and ustic moisture regimes along with mesic, thermic and hyperthemic temperature regimes. Based on the previous soil survey maps of Fars province, 14 surface soil samples were collected. Routine physicochemical analyses and clay mineralogy were performed on soil samples. Soil reaction, texture, electrical conductivity, calcium carbonate, and gypsum were identified. Soluble potassium, exchangeable potassium, non exchangeable potassium, and mineral potassium were measured. The amounts of K forms in each sample were determined. Total K was determined following digestion (110°C) of soil 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.
Results and discussion: The soils are all calcareous (average of 43% calcium carbonate equivalent) with relatively high clay contents (average of 34 %). The different forms of K including water soluble, exchangeable, HNO3-extractable, and mineral K are also 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 230 to 436, 282 to 1235, and 2312 to 9201 mg/kg-1, respectively. The soils categorized into three groups based on the soil evolution, clay mineralogy, and total potassium. Well developed soils (Alfisols), slightly developed soils (Aridsols and Inceptisols), and non developed soils (Entisols), were categorized in groups of1, 2, and3. Except for soluble K, maximum of the other potassium forms were observed in group 1. Moreover, there was a high correlation between allpotassium forms andillite content, except for soluble potassium. Mineralogical results revealed that smectite and illite were the major clay minerals in Alfisols resulting high amount of available potassium. The differences among the soil groups in terms of clay percentages may be the results of differences in parent material. K concentration is greater in soils with higher content of calcium carbonate and this is resulted in the greater leaching of K in these soils. This is in consistent with the finding of the other authors, who concluded that calcite and gypsum have a positive effect on the concentration of K in soil solution and leaching of this element from soil.
Conclusion: The results of the present study indicated that the arid and semiarid soils of southern Iran have a relatively high content of K pools. Exchangeable and HNO3-extractable K exist in equilibrium with each other, but the exchangeability of HNO3-extractable K is greater in soils dominated with illite and montmorrilonite than other soils dominated with chlorite and palygorskite. It found that calcium carbonate content had a negative effect on different soil K pools except for water soluble K. The relationship obtained in this study will be allowed determination of soil K pools from clay mineralogy and chemical and physical properties such as exchangeable K, clay content and calcium carbonate content.
