The quantity of available phosphorus in soils is the fraction that is affected by plant removal. Potassium helps to improve disease resistance, tolerance to water stress, winter hardiness, tolerance to plant pests, and uptake efficiency of other nutrients. Potassium removal by crops under good growing conditions is usually high, and is often three to four times that of phosphorus and equal to that of nitrogen. In many cases where levels of soluble potassium in the soil are high, plants tend to take up more potassium than they need. This is called luxury consumption because the excess potassium does not increase yields.
Potassium is also mobile in soils, depending on soil texture.
Movement is greatest in course-textured sands, followed by fine sands and then clay soils. Accumulation of potassium also depends upon soil texture. The greatest accumulation generally occurs in clay soils, followed by loam and coarse-textured sands. Visual evidence of calcium deficiencies generally occurs in growing points of the plant at the fruit, stem, leaf, and root tips. Magnesium is also involved in energy metabolism in the plant and is required for protein formation.