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

Potassium, as an essential element, which its role in plant metabolism and resistance to biological and environmental stresses has been proven many times, requires accurate extraction and measurement for optimal management. The present study was conducted to investigate the effect of soil/extractant ratio on measuring 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: 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 Mahlic-3 (5:1, 10:1, and 20:1) in the Karaj soil and water research institute (SWRI). The results showed that 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, this difference is due to replacing the 2:1 ratio with a 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 20:1 ratio 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 a 10:1 ratio, all three extractants measured the amount of soil-available potassium without any significant differences. Therefore, it is suggested that all three extractants be used to determine the amount of available potassium. In addition, it seems a 10:1 ratio is a suitable ratio for measuring the amount of available potassium with minimal difference between different extractants.