Potassium Fertilization Effects on Bahiagrass Herbage Accumulation, Nutritive Value, and Tissue K Concentration.

Bahiagrass (Paspalum notatum Flugge) is the most used forage for beef cattle production in Florida. Although bahiagrass is adapted to low soil fertility conditions, there is a perception that bahiagrass pastures are declining due to insufficient K fertilization levels. Two studies were conducted to determine the effects of K and N fertilization on bahiagrass herbage accumulation (HA) and nutritive value (Experiment 1), and critical tissue K concentration (Experiment 2). Experiment 1 was conducted in two locations from May to December 2014 and 2015. Treatments were the factorial combination of three N fertilization levels (0, 50 kg ha^-1 in May, or 50 kg ha^-1 in May and August) and two levels of K fertilization (0 or 50 K₂O kg ha^-1) in a randomized complete block design with three replicates. Plots (12 x 15 m) were harvested every 6 wk. Potassium fertilization did not affect HA, crude protein, and in vitro digestible organic matter concentrations; however, tissue K concentration increased from 10.6 to 11.2 g kg^-1 with increasing K fertilization levels. Plots fertilized with N had greater HA than control but there was no difference between plots fertilized in May only or May and August. Experiment 2 was conducted in a greenhouse in 2014 and 2015 with a factorial combination of three levels of N fertilization (0, 50, and 100 kg ha^-1) and four levels of potassium fertilization (0, 20, 40, and 80 kg K₂O ha^-1) distributed in a completely randomized design with four replicates. There was a quadratic correlation between K tissue concentration and HA and maximum HA occurred with K tissue concentration of 17 g kg^-1. Potassium fertilization levels greater than 50 K₂O kg ha^-1 may be necessary to increase HA of bahiagrass pastures with limited N fertilization; however, fertilization decisions should be based on agronomic aspects and economic viability.