Nitrogen Fertilization or Legumes in Tall Fescue Pastures Affect Soil and Forage Nitrogen

Including legumes in pastures improves forage quality and may reduce nitrate leaching into ground water. In a six-year grazing experiment, ‘Kentucky 31’ tall fescue (Festuca arundinacea Schreb.) was fertilized with N at 80 lb/acre each August and April or was grown with either alfalfa (Medicago sativa L.) or red clover (Trifolium pratense L.) without N fertilizer with three replicates of each system in a randomized design. Stockpiled forages were winter grazed by stocker cattle and summer forages were harvested as hay. Soils were mixed Typic Hapludults. During years five and six, effects of N fertilization or the legume on soil N, N uptake, and forage yield were investigated. Soil NH4 and NO3 were higher in the A than B horizon. Soil NH4 was higher and NO3 was lower in fescue-red clover soils than where N-fertilized fescue or fescue-alfalfa was grown. Soil nitrate did not exceed 3 ppm. Annual nitrogen uptake for the two sampling years in fescue-red clover, fescue-alfalfa, and N-fertilized grass was 239, 277, and 162 lb of N per acre, respectively, with annual biomass yields of 4.7, 5.8, and 4.7 tons/acre. After six years, potential for NO3 leaching beyond the B horizon appeared low but may be influenced by legume species.