Nitrogen Fertilization of Tall Fescue‐Birdsfoot Trefoil Mixtures

AbstractIn mixtures with birdsfoot trefoil (Lotus corniculatus L.), tall fescue (Festuca arundinacea Schreb.) growth during early spring and autumn in north Georgia is limited. A study was conducted to determine if supplemental N fertilizer could extend the productive season of tall fescue‐birdsfoot trefoil mixtures. Field experiments were conducted for 3 yr in the Mountain and Piedmont regions of Georgia. Mixtures grown included ‘AU Triumph’ tall fescue with ‘Fergus’ or ‘AU Dewey’ birdsfoot trefoil and tall fescue alone, all with N rates of 0, 56, or 112 kg ha−1 in February, or 56 kg ha−1 in February and September. The grass‐legume mixture at 0 N had total forage yields similar to tall fescue + 112 kg N ha−1. Spring production of tall fescue‐birdsfoot trefoil mixtures was increased 50 to 114% with 56 kg N ha−1. Autumn production was increased 80 to 200% with 56 kg N ha−1 in September. The N concentration of non‐N‐fertilized tall fescue increased 24% when grown with birdsfoot trefoil. Apparent N2 fixation of birdsfoot trefoil grown with tall fescue ranged from 79 to 137 kg N ha−1 during a good rainfall year. Birdsfoot trefoil apparently did not fix sufficient N for cool season growth of tall fescue, so that application of N in February and again in September extended the productive season of tall fescue‐birdsfoot trefoil mixtures.