Plants that are low in potassium have a greatly reduced ability to resist infection via fungal bacterial organisms and viral diseases. There must be enough potassium (K) in the soil to provide the proper rate and nutrient balance for each individual plant. Applying properly-balanced fertilizer with enough potassium helps improve crop quality, including crop yield and less diseased seed. Certain physical signs show when a plant is too low in potassium.
Thin Cell Walls
The plant cell wall gives the plant lateral strength. It coats the outside the plant's plasma membrane and helps keep the plant rigid. Also, the porosity of the cell wall allows only certain soluble factors to penetrate and interact with the plasma membrane. Should the cell walls become thin, it will not do its job to keep fungal bacterial organisms and viral disease organisms from penetrating itself and affecting the plant. This also promotes weakened stalks and stems.
Sugar Accumulation in the Leaves
In a study by the International Society for Horticultural Science, it was found that excessive carbohydrate (sugar) buildup in plant leaves affects the photosynthesis process of the plant. The leaves with excess sugar had less photochemical efficiency. If a plant cannot efficiently complete the photosynthesis process (breathing), it becomes weak. Once a plant becomes weak, it is a free-for-all for fungal bacterial organisms, viral disease organisms and pests to attack it.
Accumulation of Unused Nitrogen
Just as too little nutrients can be damaging to plant, so can too much of a nutrient. If a plant cannot use all the nitrogen provided to it, the toxicity of the unused nitrogen causes the plant to go into stress. When too much nitrogen is introduced, the cells in the leaves and shoots die. Stress caused by too much nitrogen may also cause premature leaf abscission. This diminishes the canopy, thereby reducing the photosynthetic capabilities of the plant, which in turn reduces energy and encourages the plant to grow and to repair itself.