Potassium (K)
Potassium (K), unlike both N and P, is not incorporated into organic compounds within the plant. The primary role of K in the plant is that of an osmotic regulator as the potassium ion. The K ion also plays an important role in stomatal regulation which in turn regulates water use and loss. During the period of fiber elongation in the cotton crop proper K fertility is critical. The fiber elongation process is controlled by the movement of water into the elongating fiber cell. This movement of water is osmotically controlled primarily by the K ion. Research has indicated a significant relationship between proper K fertility in the plant and fiber quality, particularly length.
Soil K levels are often sufficient for cotton crop production. However in some cases the labile or available quantity of K in the soil solution is unable to keep pace with demand of the crop particularly during the boll-filling period. In these instances supplemental K delivered through K fertilization has proven effective in increasing both yield and quality. This situation is typically encountered in coarser textured soils or soils comprised primarily by non K bearing minerals or when cotton follows a crop that is a high K user such as alfalfa.
Soil testing is an effective technique for predicting in-season K needs. State specific recommendations for soil test levels may be found in the ‘Resources from Individual States’ section. Keep in mind however that most commercial soil tests for K will provide an indication of the amount of labile or available K in the soil at that time.
Deficiency symptoms of cotton begin to appear as an interveinal chlorosis on the older tissue. As the deficiency progresses an orange-bronze color begins to appear on the leaf while the leaf edges begin to curl downward. Under severe deficiency scenarios, necrotic patches begin to develop along leaf margins.
| Growth Stage | Petiole Potassium Concentration (ppm) |
|---|---|
| First Bloom | 45,000 |
| Peak Bloom | 30,000 |
| First Open Boll | 15,000 |
| Late Season | 10,000 |
Potassium deficiency symptoms
