Potassium Fertilization of Bermudagrass Pastures and Hayfields

April, 2014
Maria Silveira, Joao Vendramini, and Ed Jennings
UF/IFAS, Range Cattle REC, Ona and Pasco County Extension Office, Bushnell

Potassium (K) is an essential nutrient for forage production in Florida required by plants in higher amounts than any other nutrient except nitrogen (N). On average, one ton of harvested bermudagrass [ Cynondon dactylon (L.) Pers.] forage removes approximately 45 lb of K2O. Bermudagrass yield and stand persistence are highly dependent on adequate soil K supply and as soils become depleted in K, crop responses to added K can be as great as those observed for added N. Several studies observed significant bermudagrass yield increases in response to K fertilization. In a study in Arkansas, Slaton et al. (2007) observed approximately 20% bermudagrass yield increase when K was annually applied at 100 lb K2O/A compared to control (no K application) treatments. In 4-year study in Texas, Haby et al. (2007) observed a 22% bermudagrass yield increase when K was applied at 134 K2O/A compared to zero K application. Nelson et al. (1983) observed a 50% yield increase when K was annually applied at 170 lb K2O/A on a fine sandy loam soil in east Texas. In Florida, a field study currently being conducted at the University of Florida/IFAS Range Cattle REC in Ona indicated ‘Jiggs’ bermudagrass yields in 2012 increased 45% when K was annually applied at 80 lb K20/A relative to zero K application. In addition to yield increases, many studies have also demonstrated that adequate levels of soil K reduce bermudagrass winter injury and survival after freezing temperatures. Potassium fertilization has also been linked to rhizome production, root development, stand persistence, and plant resistance to diseases and pests injury. When K is deficient, winter kill is greater, stand persistence diminishes, forage production is reduced, and profitability can be detrimentally affected. First visual signs of stand decline are often observed in the initial spring regrowth. Soil test along with tissue analysis can provide a good estimate of K status. Despite the limited information on critical K tissue level adequate to maintain production and sustainability of various bermudagrass cultivars in Florida, data in the literature suggest that 1.5% appears to be a reasonable estimate. In Florida, potassium fertilization is not recommended when soil test levels are above medium (36 to 60 parts per million Mehlich-1 K) level.

Despite its important role in sustaining bermudagrass stands, K fertilization has received much less attention than N Fertilization. Unfortunately, many forage production systems do not supply adequate K to replace that removed with harvested forage and, consequently, soil K supply becomes deficient. Numerous field observations in Florida suggest the importance of K fertilization of highly productive bermudagrass cultivars. Despite bermudagrass’ ability to effectively extract soil K to very low levels, there have been many cases of bermudagrass decline reported in Florida as a result of K deficiency. These failures are typically observed in more intensive production systems such as hayfields where the grass is harvested up to five times a year over long periods of time. This is partially due to the fact that depletion of soil K can occur within relatively short periods even in soils with adequate soil K levels when large amounts of forage are harvested. In addition, it is not uncommon to see soil fertilization practices focused solely on N fertilization. Because most soils used for forage production in Florida exhibit poor fertility conditions and relatively low K concentrations, low K supply in the soil may also limit the ability of the plants to utilize the applied N. While addition of N increases yield, it also stimulates additional uptake of other nutrients. Several studies observed that greater rates of K are required to obtain higher yields expected at higher N rates. If soil K supply is low, yield increase in response to N fertilization can also be reduced. As the soil reserves became more depleted in K, marginal crop responses to added N (or any other nutrient) are expected to occur.

Moreover, because sandy soils often exhibit low cation exchange capacity and, therefore, limited ability to retain K even after receiving K fertilizer, repeated application of K is often required to meet plant requirements. Potassium application rate, frequency, and time of application are important considerations for bermudagrass production in Florida soils. Intensive management, especially high N applications, increase yield responses to K fertilization. Various reports in the early 70’s concluded that Coastal bermudagrass required between 200 to 400 lb K20/A per year. Corroborating these early studies, Robinson et al. (1990) observed maximum yields at the 300 lb K2O/A rate. Although these relatively high K application rates can increase bermudagrass yields, they are likely not economical on many production systems. Similarly, maintaining soil test K at medium or higher levels can be highly expensive and difficult to achieve in Florida soils. On the other hand, because extreme low K supply may also represent an economic risk, efforts should be focus on replacing K removed with harvested forage. According to the University of Florida/IFAS fertilizer recommendations for bermudagrass hay production, K should be applied at rates of 40 to 80 lb K20/A (if soil is very low or medium in K, respectively) in early spring.  An additional 40 lb K2O/A should be applied after each harvest, except the last in the fall. Despite limited research data, there are evidences in the literature showing that fall application of K to bermudagrass is advantageous and may help protect the grass against cold damage. For maintenance of established bermudagrass pastures, 50% of K20 should be applied in early spring and the remaining K2O in mid- to late-season. Research is currently being conducted at the University of Florida /IFAS Range Cattle REC to determine the minimum K fertilization regimens that can maintain optimum forage yield, nutritive value, and stand persistence. In addition, on-farm demonstration plots in Pasco and Sumter Counties are also evaluating bermudagrass responses to K fertilization in fields that exhibited significant stand loss and very poor regrowth after winter kill.

Haby, V.A., W.M. Stewart, and A.T. Leonard. 2007. Tifton 85 bermudagrass response to potassium sources and sulfur. Better Crops, Vol. 91, Pages 3-5.

Nelson, L.R., T.C. Keisling, and F.M. Rouquette, Jr. 1983. Potassium rates and sources for Coastal bermudagrass. Soil Science Society of America Journal, Vol. 47, Pages 963-966.

Robinson, D.L. M.S. Miller, and D.J.R. Cherney. 1990. Potassium fertilizer influences on Coastal bermudagrass yield and nutrient uptake and on available soil potassium levels. Communications in Soil Science and Plant Analysis, Vol. 21, Pages 753-769.

Slaton, N.A., R.E. DeLong, C.G. Massey, B.R. Golden, and E.T. Maschmann. 2007. Bermudagrass forage response to potassium fertilization. In: N.A. Slaton (ed.). Arkansas Agricultural Experiment Station Research Series 558:64-68. Fayetteville, AK.

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