Soil Nutrient Cycling
Potassium Cycle
Potassium, much like phosphorus, exists in pools with differing abilities to replenish crop available potassium. In soil, potassium occurs in four pools: soil solution, exchangeable, fixed, and primary (i.e., parent) minerals. At any one time, most soil potassium is in fixed and primary minerals forms. Plant available potassium includes solution potassium and exchangeable potassium. Potassium in the soil solution (soluble potassium) is readily available, and plant roots can immediately take it up. Exchangeable potassium is weakly adsorbed to the surfaces of soil particles and can rapidly replenish soil solution potassium.
Processes Affecting the Availability of Potassium
The processes governing the availability of potassium are mineral weathering, clay fixation and release, adsorption and desorption, leaching, erosion, and plant uptake. Mica and feldspar and mica minerals are common parent materials for most soils. Micas, especially biotite, weather faster and release their potassium much more readily than do feldspars. Feldspars are very resistant to weathering and are often found in sands, while the less resistant micas are a constituent of almost all silt and clay fractions.
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