Runoff/Erosion -
Water that doesn’t infiltrate soil and is lost by surface flow is runoff. Erosion refers to the wearing away of land and soil surface through rain, irrigation, wind, and ice. Both of these actions result in lost nutrients, including potassium, from the soil.
Crop Harvest -
This represents the amount of potassium removed in the grain or harvested portion of the plant. Crops that use more leaves and stems, like alfalfa, remove more potassium than grain crops. Use our nutrient removal calculator to find out how much potassium, and other nutrients, you should be replacing.
Plant Residue +
This is potassium that’s recycled to the soil and is calculated by crop uptake minus grain removal – e.g., in corn 1.10 lb./bu. can be returned to the soil. In a corn crop, potassium releases back to the soil shortly after the plant reaches physical maturity. Unlike nitrogen and phosphorus, potassium has no organic form in tissue and doesn’t require mineralization by microorganisms to become available to plants.
Mineral Fertilizer +
Applying fertilizers that include potash (KCL), sulfate of potash (K2SO4) and potassium nitrate (KNO3) adds to the soluble-K fraction in the soil.
Animal Manure/Biosolids +
These organic materials provide potassium as an accompanying cation (K+).
Leaching -
Water can remove soluble nutrients from one zone of the soil to another. Leaching happens most often in sandy soils (with low cation exchange capacity) and high organic matter soils.
Soil Solution
Potassium is relatively immobile in soil and reaches plant roots mostly by diffusing in the soil solution – the liquid phase of soil.
Desorption
The opposite of adsorption, desorption is the movement of adsorbed potassium off the adsorption sites.
Adsorption
This happens when potassium ions are taken up from the soil solution and held on the surface of solids by chemical or physical binding.
Mineral Potassium
Also known as feldspar, mineral potassium must weather in the soil to become available to plants – a process that can take hundreds of years and add significant amounts of available potassium to the soil.
Fixed Potassium
When clay soils shrink and swell during dry and wet weather, water-soluble potassium moves or converts into the clay and becomes “fixed” within clay layers.
Exchangeable Potassium
This potassium is held on the cation exchange complex (CEC) and is in constant equilibrium with the soil solution potassium. As plants take up potassium from the soil solution, potassium is released from the CEC.