Dinitrogen Fixation and Nitrogen Transfer in Birdsfoot Trefoil-Orchardgrass Communities
Birdsfoot trefoil (Lotus comiculatus L.) is an important perennial forage legume used primarily for pasture. Despite its traditional usage as a source of nitrogen for cropping systems, little information is available on the amounts of atmospheric dinitrogen (N2) that birdsfoot trefoil fixes or transfers to an associated grass during long-term stands. Field research was undertaken to compare N2 fixation and N transfer potentials of three birdsfoot trefoil cultivars and one experimental line (hereafter referred to collectively as the birdsfoot trefoil cultivars). These were seeded in binary mixtures with orchardgrass (Dactylis glomerata L.). Dinitrogen fixation and N transfer were estimated by 15N isotope dilution, using orchardgrass pure stands as a reference. Over the 2-yr study, percentage legume N derived from fixation ranged from 93 to 95% among the birdsfoot trefoil cultivars. Dinitrogen fixation usually did not differ among cultivars within harvests. Total-season fixed-N yields among cultivars for the two years ranged from 90 to 138 kg ha−1. Percentage orchardgrass N derived from N2 fixation and N transfer ranged from 8 to 46%. Nitrogen transfer did not differ among birdsfoot trefoil cultivars at any harvest. Total-season transferred-N yields ranged from 4 to 42 kg ha−1, with no differences among cultivars. Under the conditions of this study, the birdsfoot trefoil cultivars tested generally did not differ in their abilities to fix atmospheric N2 or to transfer fixed N to associated orchardgrass.
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