The chemistry and dynamics of soil potassium: impacts on crop nutrition and fertilizer management

Abstract

Potassium (K) is a vital macronutrient, second only to nitrogen in plant uptake, playing essential roles in enzyme activation, osmotic regulation, and carbohydrate transport. Soil potassium exists in dynamic equilibrium in four forms viz., water soluble (WSK), exchangeable (Exch K), non-exchangeable (NEK) and lattice K, of which the first two are important for the growth of higher plants and microbes. A large portion of the total K in soil occurs as structural component of soil minerals and is unavailable to plants. Plants can use only the Exch-K present on the surface of soil particles and the K dissolved in soil water. This often constitutes very small fraction of the total soil K. The dynamics of K in soil depends on the magnitude of equilibrium among various forms which have relationship with physicochemical properties. Intensive agriculture, especially in India, often overlooks crop-specific K requirements, applying uniform fertilizer doses that fail to compensate for K removal by high-yielding crops. This imbalance has led to progressive depletion of labile K and increased dependence on non-exchangeable pools, risking long-term soil fertility. Soil properties such as mineralogy, clay content, and organic matter significantly influence K availability and transformation among pools. An integrated nutrient management (INM) approach combining inorganic fertilizers with organic amendments like farmyard manure (FYM) is essential to enhance K mobilization and maintain soil health. Understanding the dynamics of K forms and their interactions is critical for developing efficient, site-specific K management strategies. This paper underscores the importance of balancing K inputs with crop demands to sustain productivity and soil quality in intensively managed agricultural systems.