Soil Nutrient management
Potassium
Forms of Potassium Taken up by Plants
Potassium exists mainly in four forms in the soil: soil solution, exchangeable, nonexchangeable (fixed), and mineral potassium. Plants absorb the ionic forms of potassium (K+) from the soil solution which is immediately available to plants.
Potassium Deficiency in Plants
Growers experience potassium deficiencies less often than those of other primary nutrients. In general, when potassium is deficient tissue at the tips and edges of the oldest leaves begin to yellow (chlorosis) and then die (necrosis), so that the leaves appear to have been burned on the edges. Because potassium is very mobile within the plant, it is translocated from older tissues to younger ones if the supply becomes inadequate. The symptoms of deficiency therefore usually occur earliest and most severely on the oldest leaves.
Potassium Toxicity in Plants
Although plants can suffer from nitrogen and phosphorus toxicity, interestingly enough, potassium toxicity is exceedingly rare. It is very difficult for plants to access too much potassium. While potassium toxicity usually won’t cause direct problems in plants, it can cause deficiencies in other nutrients, like calcium and magnesium.
Mobility of Soil Potassium
Potassium is generally immobile in soil because it is a positively charged ion that is held tightly by negatively charged soil particles but moves more readily in soil than does phosphorus.
Management of Soil Potassium
Plant uptake of potassium is affected by many factors. Generally, uptake is largely influenced by conditions that favor and increase root system development. Warm soils, adequate soil moisture, good aeration, and lack of root restriction typically allow for the greatest uptake. Fertilizer and manure application rate and timing are often based on the optimal nitrogen rate and not on potassium requirements.
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