Concentrations of Mg, Ca, P, K, and Crude Protein in Fertilized Tall Fescue1

Abstract

AbstractTall fescue (Festuca arundinacea Schreb.) pastures have been implicated with the occurrence of grass tetany in the eastern U.S.A. Grass tetany problems would probably be reduced if Mg concentration in tall fescue forage were increased. The purpose of this study was to examine the effects of Mg, NPK, and N fertilizers on Mg and other major nutrients in tall fescue grown on a soil already high in Mg. A randomized complete block factorial experiment was conducted for 2 years on an Etowah silt loam (line‐loamy, siliceous, thermic, Typic Paleudults).Tall fescue was fertilized in August of 2 successive years with 0, 84, or 168 kg Mg/ha from MgSO4 . 7H2O and 67‐29‐56 or 134‐58‐112 kg N, P, K/ha from a complete NPK fertilizer; and in December with 0 or 67 kg N/ha from NH4NO3. Forage was harvested five times during the growing season and stockpiled forage was harvested in December. The Mg concentration in forage was increased by Mg and N application and was not affected by NPK rate. Calcium was decreased by N. Potassium was slightly increased by NPK fertilization.Forage Mg was above 0.20% for all sampling dates and K/(Ca + Mg) ratios were below 2.2, so the grass tetany hazard from this forage was probably low. Soil test Mg levels increased in response to Mg fertilization, but soil Mg levels were not affected by NPK or N fertilization. Temperature of the growth period had a greater influence on forage Mg than the fertilization treatments on this soil which was already high in Mg.