Potassium dynamics in three alluvial soils differing in clay contents

Despite the presence of a huge amount of potassium (K^+) in the soil, most of the soils are deficient in plant available K^+. A large amount of the K^+ is fixed by clay minerals present in such soils and cannot be taken up by plants to achieve optimum plant growth. In such type of soils, large amount of K^+ fertilizers are required for optimum plant growth, as plants do not respond enough to a normally recommended K^+ fertilization. Vermiculite clay minerals can fix an enormous amount of applied K^+, which becomes slowly available to the plants. The K^+ dynamics in such soils are valuable to recommend K^+ fertilizer requirements for sustainable nutrient management. We analyzed the K^+ dynamics of three alluvial soils, i.e Kleinlinden, Giessen and Trebur, collected from Germany and found that the soils with vermiculite and smectite clay minerals have more K^+- fixing ability than soils dominated by illite clay minerals. However, as the K^+ concentration decreased in the soil solution, smectite-dominant soils may easily release fixed K^+ due to lower particle-charge, whereas vermiculite and illite dominant soils may not release fixed K^+ easily. Moreover, ammonium exchangeable K^+, non-exchangeable K^+, total K^+ and K^+-fixing capacity of these soils are directly proportional to the soil clay contents. While recommending K^+ fertilizers clay contents and the type of clay minerals is not considered and recommended K^+ fertilizers sometimes do not response plant growth enhancement. Therefore potassium fertilizer should be recommended by taking into consideration the type and amount of clay minerals present in the soil.