The effect of extractant type and soil to extractant ratio on the extraction of soil available potassium

Document Type : Research Paper


1 Soil and Water Research Institute, Agricultural Research, Education, and Extension Organization, Karaj, Iran

2 Department of Soil Science, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran

3 Agricultural Research, Education and Extension Organization (AREEO), Soil and Water Research Institute (SWRI), Karaj, Iran


Potassium, as an essential element, which its a role in plant metabolism and resistance to biological and environmental stresses has been proven many times, and requires accurate extraction and estimation for optimal management. The present study was conducted to investigate the effect of soil to extractant ratio in estimating the amount of available potassium in the soil. For this purpose, in October 2021, 62 soil samples were taken from agricultural fields all over the country and their potassium content was measured by three extractants, namely 1 M ammonium acetate (three ratios of 5:1, 10:1, and 20:1), ammonium bicarbonate-DTPA (2:1, 5:1 and 10:1) and Mehlich-3 (5:1, 10:1 and 20:1) in Karaj soil and water research institute (SWRI). The results showed the amount of available potassium measured by ammonium acetate and Mehlich-3 extractants had no significant difference, but these two extractants had a significant difference with ammonium bicarbonate-DTPA. Probably, the reason for this difference is replacing the 2:1 ratio with the 20:1 ratio in the extraction method by ammonium bicarbonate-DTPA. In all three extractants, the estimated soil available potassium increased by increasing the soil to extractant ratio. On average, the amount of extracted potassium in the ratio of 20:1 was 11.5% and 5.01% more than the ratio of 5:1 and 10:1 for ammonium acetate, and 8.79% and 6.84% more than the ratios of 10:1 and 5:1 for Mehlich-3, respectively. By using the 10:1 ratio, all three extractants estimated the amount of soil available potassium without any significant difference. Therefore, suggested that all three extractants can be used to determine the amount of available potassium. In addition, it seems the 10:1 ratio is a suitable ratio for estimating the amount of available potassium with minimal difference between different extractants.


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