Bermudagrass Forage Response to Phosphorus and Potassium Fertilization

Introduction

Warm- and cool-season forages cultivated for hay production are grown on about 1.4 million acres in Arkansas (USDA-NASS, 2023). Bermudagrass [Cynodon dactylon (L.) Pers.] is grown for hay and pasture which helps sustain cattle production in western Arkansas. Phosphorus (P) and potassium (K) are essential macronutrients for forage production. Forage uptake and removal of N and K are nearly equal (≈45 lb N or K/ton forage) and eight to ten times greater than P uptake and removal (≈5 lb P/ton). Poultry litter has been the primary soil amendment and nutrient source applied to forages in western Arkansas for years. However, the use of poultry litter as a nutrient source is now limited or prohibited due to regulations that limit the rate or sometimes prohibit its application on soils that contain high soil-test P or have features that are conducive to P transport via run-off. Sustaining high forage yields will require judicious use of inorganic fertilizer and soil amendments. Growers may choose to apply little or no fertilizer and produce forage yields that are likely to be low and decline over time or apply commercial fertilizer to eliminate these nutrients as yield limiting factors.

Objective: Field trials were initiated in 2006 to collect data that describe the relationships between soil-test P and K, nutrient uptake, and bermudagrass forage yield responses to fertilizer-P and -K rates.

Materials and Method

Site Description

Fertilization trials were initiated in April 2006 in a field of established to common bermudagrass on a Captina silt loam (Fine-silty, siliceous, active, mesic Typic Fragiudults) at the Shult Agricultural Research Experiment Station (MAES30) located in Fayetteville, Arkansas, in April 2007, in a commercial field (CityFarm) of established ‘Midland’ bermudagrass on a Johnsburg silt loam (Fine-silty, mixed, active, mesic Aquic Fragiudults) near Fayetteville, Arkansas, and in April 2011 on a Barling silt loam (Coarse-silty, mixed, active, thermic Fluvaquentic Dystrudepts) with an established stand of ‘Midland 99’ bermudagrass on a commercial farm (ElPaso) located near El Paso, Arkansas. The Captina soil had been used for hay production and grazing with a history of manure application. The Johnsburg silt loam had received biosolid applications for several years, but none since 2003 and was used only for hay production. The Captina site was managed with no irrigation, but the Johnsburg site was irrigated once in early September 2007. The plots were 20-ft long and 5-ft (MAES30) or 6-ft (CityFarm and ElPaso) wide. The MAES30 trials were established and maintained for 5 consecutive years (2006-2010), whereas the CityFarm (2007-2008) and ElPaso (2011-2012) trials were maintained for 2 consecutive years. The forage at each site was not a pure stand of bermudagrass and contained other warm-season grasses (see the annual W. E. Sabbe Arkansas soil fertility studies publications).

Soil Analysis

Composite soil samples were collected from each plot to a depth of 4 inches to determine the initial soil chemical properties and uniformity among plots. Each composite soil sample consisted of eight soil cores. Soils were dried at 120-130°F, crushed to pass a 2-mm diameter sieve, analyzed for water pH (1:2 soil weight to water volume ratio; Sikora et al., 2014), and extracted for plant-available nutrients using the Mehlich-3 method (Zhang et al., 2014). Soil organic matter was determined on selected samples using the loss on ignition method (Zhang & Wang, 2014). Pelletized lime (1000 lb/acre) was applied to the MAES30 on 27 September 2006 to adjust the soil pH. The P-rates and K-rates experiments were randomized complete block designs with each fertilizer rate replicated five times.

Phosphorus Treatments Application

Triple superphosphate was applied in 1-3 three split applications for five season-total fertilizer-P rates plus a no-P control. Phosphorus fertilizer treatments were applied before green-up and following the first and second harvests. Blanket application of 100 lb K₂O/acre was applied before green-up and repeated when N fertilizer was applied to each site. The green-up application of N fertilizer consisted of 100 lb (NH₄)₂SO₄/acre plus 300 lb NH₄NO₃/acre at each site (≈120 lb N/acre). Following each harvest on the Captina, 120 lb N/acre (358 lb NH₄NO₃/acre) was applied to stimulate forage production resulting in a season total of 360 lb N/acre. For the Johnsburg soil, 90 lb N/acre as NH₄NO₃ was applied following each harvest for a season total of 300 lb N/acre. For the Barling soil, 150 lb muriate of potash/acre and 260 lb urea/acre were applied at green-up. Following each harvest, the trial on the Barling soil received 150 lb muriate of potash and 80 to 100 lb urea-N/acre.

Potassium Treatments Application

Muriate of potash was applied in 1-3 split applications for five fertilizer-K rates plus a no-K control. Potassium treatments were applied before green-up and following the first and second harvests. Blanket application of 100 lb triple superphosphate/acre, 100 lb (NH₄)₂SO₄/acre, and 300 lb NH₄NO₃/acre were applied (≈120 lb N/acre) to the Captina and Johnsburg sites. Following each harvest on the Captina, applications of 120 lb N/acre as NH₄NO₃ were made to stimulate forage production resulting in a season-total N rate of 360 lb N/acre. For the Johnsburg soil, 90 lb N/acre as NH₄NO₃ was applied following each harvest for a season total of ~300 lb N/acre. For the trial on the Barling soil, P [150 lb 12-40-0-10S-1Zn/acre, sold as MicroEssentials (MESZ)] and N fertilizers (260 lb urea/acre) were applied at green-up. After subsequent harvests, the trials received 80 to 100 lb urea-N plus 100 lb MESZ or ammonium sulfate/acre.

Weed Management

Weed control at the MAES30 site was performed by applying glyphosate (Roundup WeatherMax at 1 pt/acre) before green-up to suppress/control winter weeds in 2007. Cimarron Max (2 qt/acre of 2,4-D + dicamba plus 0.5 oz metsulfuron/acre) was applied following the first harvest in 2006 and 2009 primarily to control buckhorn plantain.

Harvest

Bermudagrass forage was harvested by cutting an 18-ft long by 3.8-ft wide swath with a self-propelled sickle-bar mower at a height of 2.0 to 2.5 inches. The forage was harvested 3-4 times a year at a targeted interval of 28-35 days. Some harvest times were delayed due to poor growth caused by lack of rainfall. The freshly cut biomass from each plot was weighed and eventually adjusted to a total dry weight expressed as lb dry forage/acre by recording the weight (≈500 g) of a subsample of fresh forage which was subsequently dried to a constant weight in a forced draft oven at 60°C and weighed again for dry weight. A shrink factor was calculated and used to adjust total fresh forage weight to a dry weight basis. Subsamples of forage were ground to pass a 1-mm sieve and digested in concentrated HNO₃ and 30% H₂O₂ to determine forage P and K concentrations and calculation of K uptake and removal.

Annual reports of the trials published by Slaton et al. (2006, 2007, 2008, 2009, 2010, 2011, & 2012) in W. E. Sabbe Arkansas soil fertility studies, research series 548, 558, 569, 578, 588, 599, and 608 (https://scholarworks.uark.edu/aaesser/) provide additional details on the management.

Funding for forage studies was provided by Fertilizer Tonnage Fees administered by the Arkansas Soil Test Review Board and the University of Arkansas System Division of Agriculture.

References

Sikora, F. J., & Kissel, D. E. (2014). Soil pH. In Sikora F. J. & K. P. Moore (Eds), Soil test methods from the southeastern United States (pp. 48–53). Southern Cooperative Series Bulletin 419. Athens, GA: University of Georgia. http://aesl.ces.uga.edu/sera6/PUB/MethodsManualFinalSERA6.pdf

USDA-NASS. United States Department of Agriculture, National Agricultural Statistics Service. 2023. Available at https://quickstats.nass.usda.gov/results/F1704B27-0098-3977-97C4-17C12DE026D6 [Accessed on 12/08/2023]

Zhang, H., Hardy, D. H., Mylavarapu, R., & Wang, J. J. (2014). Mehlich-3. In Sikora F. J. & Moore K. P. (Eds), Soil test methods from the southeastern United States (pp. 101–110). Southern Cooperative Series Bulletin 419. Athens, GA: University of Georgia. http://aesl.ces.uga.edu/sera6/PUB/MethodsManualFinalSERA6.pdf

Zhang, H., & Wang, J. J. (2014). Loss on Ignition. In Sikora F. J. & Moore K. P. (Eds), Soil test methods from the southeastern United States (pp. 155–157). Southern Cooperative Series Bulletin 419. Athens, GA: University of Georgia. http://aesl.ces.uga.edu/sera6/PUB/MethodsManualFinalSERA6.pdf