Study of Factors Influencing Potassium and Ammonium Fixation in the Soil, Clay Minerals and its Roles in Potassium Fertilizer Consumption

Potassium and ammonium fixation is one of the most important factors that influence the availability of these ions in the soil. Type of clay minerals, charge density, potassium and ammonium saturation percentage, concentration of potassium and ammonium ions in soil solution, wetting and drying cycles, soil moisture content, soil pH and the amount of soil organic matter are the most common and important factors affecting the fixation of potassium and ammonium in clays and soils. These cations have the same ionic radius and, therefore have same behavior to be fixed by clay minerals. Application of ammonium and potassium fertilizers together can decrease fixation capacity of these ions, and improve uptake of these ions by plants. Application of ammonium ions can decrease potassium fixation in the soil and, therefore it can increase potassium availability for plants and reversible. This result has important effect on economic and management of fertilizers application, and should be considered for the application of nitrogen and potassium fertilizers. Therefore, study the attribute factors on NH4 and K fixation and its competitions can lead us to better management for these components and can help for selection of best program for fertilizer management and could be used for a good program for effect of clay mineral fixation. According to this, by application of NH4 fertilizers, such as urea, K release from clay mineral will be increased. Therefore, K for plant uptake will be provided. We attempt to elaborate a review for evaluation of K and NH4 fixation and affected factors on this process in soil. Finlay strategy for the optimum usage of these elemental fertilizers in plant nutrition will be proposed.