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. According to Dr. Dennis Hancock, UGA
Extension Forage Specialist, poor K fertility is one of the top 10 causes for
stand loss. (View all top 10 causes in
this video http://www.youtube.com/watch?v=_EADtbQsbAg.)
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 b efore 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.
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Leafspot disease can be a result of K
deficiency.
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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”.
Carole Knight
UGA Cooperative Extension – Bulloch County Ag Agent
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