Document Type : Research Article
Authors
1 Department of Soil Science and Engineering, Faculty of Agriculture, Shahrekord University, Km 2 Saman Road, Shahrekord, Iran
2 Department of Soil Science and Engineering, Faculty of Agriculture, Shahrekord University, Shahrekord, Iran
3 Department of Soil Science Engineering, Faculty of Agriculture, Shahid Bahonar University of Kerman, Kerman, Kerman , Iran
Abstract
Introduction
One of the macronutrients essential for plant growth is potassium and plays significant physiological and biochemical roles in plant yield. There are four forms of potassium in the soil, listed in order of their availability for plant uptake: soluble potassium, exchangeable potassium, non-exchangeable potassium, and structural potassium. Determining the concentration of available potassium using an efficient extractant that is applicable to different soil types is essential for soil and crop management, such as fertilizer recommendations. One of the most common extractants for available potassium is 1N ammonium acetate (NH4OAC). This extractant is widely used in many soil science studies and fertilizer recommendations due to its ability to extract exchangeable potassium and a portion of non-exchangeable potassium. However, this method may not have sufficient accuracy to measure the potassium readily available for plant uptake. In soils with high amounts of potassium-containing minerals, due to the presence of specific adsorption sites, a large portion of potassium is held strongly at these sites and can be extracted partially during NH4OAC extraction. This issue could be one reason for the weak correlation between NH4OAC extracted potassium and plant response to potassium fertilizer in such soils. The critical level of available potassium is the threshold below which plant growth is limited. Since the amount of potassium extracted depends on the concentration of the extractant, evaluating the effect of different NH4OAC concentrations on determining the critical level is important. The objective of this study was to assess the impact of various NH4OAC concentrations on the extraction of available potassium and to determine the critical potassium level in the calcareous soils of Shahrekord Plain.
Material and methods
In order to evaluate different concentrations of NH4OAC in the calcareous soils of the Shahrekord plain, 30 agricultural soil samples were collected from a depth of 0–30 cm. four different concentrations of NH4OAC including; 1, 0.5, 0.25 and 1 molar were evaluated for extracting available potassium. The greenhouse experiment was carried out as a factorial in the form of completely randomized design with two factor; 30 types of soil and potash fertilizer in two levels of potassium (zero and 100 mg k kg-1) from sources of potassium sulfate with three replications. At the end of, the vegetative period, corn plants harvested and plant indices including; dry matter weight, potassium concentration, potassium uptake, relative yield and plant response were determined. To assess the significance of treatment effects in terms of plant indicators, factorial analysis of variance was performed. Then, the correlation between plant indices and potassium extracted using different concentrations of NH4OAC was calculated, and based on the results, the most suitable concentration for extracting available potassium by NH4OAC was determined. The potassium critical level was determined using the Cate-Nelson graphical method for NH4OAC extractants with concentrations of 1, 0.5, 0.25, and 0.1 molar.
Results and Discussion
The results showed The range of available potassium extracted using NH4OAC extractants at concentrations of 1, 0.5, 0.25, and 0.1 molar were 157–581, 155–598, 160–596, and 168–590 mg kg⁻¹, respectively. The results of the analysis of variance showed that the main effects of soil type and potassium fertilizer were significant (p<0.01) on dry matter weight, potassium concentration and uptake. However, the interaction between soil and fertilizer was not significant for dry matter weight. Based on the strong correlation between potassium extracted by NH4OAC at concentrations of 1, 0.5, 0.25, and 0.1 molar and the relative yield and plant response indices, these concentrations can be considered suitable for use in these soils. By using the Cate-Nelson graphical method, the potassium critical level with concentrations of 1, 0.5, 0.25, and 0.1 molar were 250, 250, 255 and 250 mg kg-1 respectively.
Conclusion
The results showed that reducing the concentration of ammonium acetate does not affect the efficiency of this extractant. The results showed that the amounts of available potassium extracted with NH4OAC at different concentrations were close to each other, with less than one percent difference. Commonly, NH4OAC 1 M is used for extracting available potassium; however, our results show that lower concentrations of NH4OAC (0.5, 0.25, and 0.1 M) can be effectively used as substitute to the 1 M solution. Therefore, it is recommended to use 0.1 molar ammonium acetate for the extraction of available potassium. This substitution could result in a considerable reduction in chemical consumption.
Acknowledgements
The authors would like to thank the Soil Science Department of the University of Shahrekord for providing equipment and facilities.
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