Potassium is for Persistence - Ag News and Views

We rely heavily on our bermudagrass pastures and hay meadows during the summer in some parts of Texas. Often times we are disappointed with production, see a thinning of our stand and/or see disease like symptoms. This is often times referred to as “Bermudagrass Decline.” We quickly blame weather. Granted weather can have an impact on each of those issues. However, there is often a deeper problem that we need to access.

Primary Causes:

Low Potassium (K) Fertility: A deficiency in K will result in poor stress tolerance, reduced winter hardiness, decreased disease resistance, and reduced rhizome and stolon production. To determine if K deficiency is causing the problem, a soil analysis will be imperative. Collect representative soil samples from the affected areas and another from areas nearby that are unaffected or less affected. More soil testing information can be located here: (http://soiltesting.tamu.edu). Potassium deficiency may occur during periods of water stress. The plant absorbs K from the soil by drawing in water from the soil that contains K. Therefore, even if the soil test indicates an adequate level of soil test K, a drought can reduce the amount of K available to the plant.
Low Soil pH: There are several ways that soil pH causes a problem. First, toxic levels of soluble Al can occur in soils where the soil pH has dropped too low. This burns back the fine root hairs and prevents root growth. Low soil pH also reduces the availability of other nutrients such as P, K, Mg, Ca, and others. Ultimately, low soil pH starves the plant of water and nutrients. Soil pH (as evaluated by soil test) showed not to be less than 5.5 for Coastal bermudagrass and 5.8 for Tifton 85 bermudagrass. Overseeded forages such as clover and ryegrass need a pH of 6.0 or higher for optimum growth.
Leaf Spot: Helminthosporium leaf spot (Bipolaris spp.) is commonly associated with bermudagrass decline. Helminthosporium leaf spot commonly attacks bermudagrass stands where K levels are low.
Ryegrass: The past two springs have been abundant with rainfall and ryegrass (volunteer or otherwise). In the spring when bermudagrass is breaking dormancy, an abundance of ryegrass can out-compete bermudagrass for water, nutrients and light. Heavy growth of ryegrass and removal as hay can deplete large amounts of K from the soil, thus effectively reducing the amount of K available to the bermudagrass. To avoid this problem, be sure to avoid late applications of N to ryegrass stands and utilize as much ryegrass forage as possible by grazing.
Drought: Bermudagrass is quite drought tolerant. However, if drought is combined with other stressors such as K and pH stress drought can be challenging for bermudagrass to handle. Remember to maintain soil fertility during good growing conditions (periods of rainfall) so if drought does become an issue bermudagrass will be better prepared, so to speak.
Poor Nutrient Management in Hay Production: Bermudagrass can be an excellent hay crop if properly managed. High rates of nitrogen fertilization with no attention to depletion of other plant nutrients (especially K) can lead to low soil potassium and the associated problems as listed above. Annual soil testing and special attention to K levels with help alleviate these problems.

Struggling Bermudagrass Hay Meadow

Improvement of Bermudagrass Hay Meadow with Weed Control, Fertilizer Application and Replanting.

Vanessa Corriher-Olson, Forage Extension Specialist, Soil & Crop Sciences, Overton, TX

vacorriher@ag.tamu.edu

Texas A&M AgriLife Extension Service, Texas A&M University System