Potassium is an essential element in plants and is considered one of the three macronutrients, along with nitrogen and phosphorus. The amount of K is reported in almost all routine soil samples. Unfortunately, with price increases, it has gone from being the least expensive to the most expensive of the three macronutrients. Ignoring the importance of potassium fertilization and not maintaining adequate soil levels can lead to forage losses and ultimate stand decline.
Potassium is essential for producing economical yields and maintaining persistence in our forages. The role of potassium is extremely important. Potassium regulates the enzymatic processes that are necessary for growth. It helps regulate water use. Potassium assists with the plants ability to withstand extreme temperatures, drought and pests. Therefore, it affects plant vigor, disease resistance, forage quality, and winter survival. Poor K fertility has been shown to be one of the top 10 reasons for forage stand loss in Georgia.
Soil type and environmental conditions have an effect on the amount of potassium available for plant use. Availability is highest under warm, moist conditions in soils that are well aerated with a neutral or slightly acidic pH. Soils that are too wet can reduce potassium uptake. In addition, soils with a high clay make-up can have reduced potassium availability; as well as very sandy soils where leaching can be an issue.
Symptoms of potassium deficiency include yellowing of the lower leaves and, in severe cases, leaf-tip dieback. Once symptoms are present, the plant’s ability to withstand stress conditions, such as high heat, drought and pests, is diminished. A bermudagrass stand may be very old before it begins to exhibit severe stand thinning as a result of K deficiency. However, some varieties are more prone to K deficiency problems than others. For example, “Alicia” is very susceptible to leafspot diseases when K deficiency occurs.
The amount of potassium needed is dependent upon the level of management. For instance, there is a high demand for potassium in a hayed bermudagrass field compared to one that is grazed. This is due to the amount of potassium removed in the hay. Each ton of bermudagrass hay will often contain the equivalent of more than 40 lbs. of K fertilizer (K2O). High-producing bermudagrass hayfields may yield well over 10 tons per acre. As a result of this high rate of nutrient removal, K deficiencies occur frequently. Potassium amounts should be applied in relation to your yield goals.
Research has shown that stands can recover if given adequate K supplementation. Soil tests should be taken and potassium fertilization recommendations adhered to.It is important to split K applications across two or more application times to prevent excess K uptake. For more information refer the UGA publication – “Soil and Fertilizer Management Considerations for Forage Systems in Georgia”.