Critical aspects of potassium management in agricultural systems

Fertilizer and manure application rate and timing are often based on the optimal nitrogen rate and not on potassium (K) requirements. This can lead to excess or shortage of K depending on the crop and rotation. In grass-dominated agricultural production, including many organic farming systems, K has become a critical element, especially in areas dominated by coarse-textured or organic soils. In this paper we review K management in relation to long-term sustainability of both the soil resource and the production of crops of high yield and quality. One question for the future is whether we can adopt management options that favour efficient use of K and secure a sustainable future for global K reserves. For example, is it possible to enhance the release rate of K from soil mineral sources so that we require less fertilizer K from K-bearing salt deposits? A reduction in external K inputs requires improved on-farm recycling of K in order to reduce losses. We also need a better understanding of soil processes and soil-plant interactions and decision-support tools to predict the potential K release from mineral weathering. Certain areas dominated by young, clay-rich soils can potentially supply enough K, whereas other areas with coarse sandy or organic soils have a very low weathering potential and would thus need external inputs of K.