DINITROGEN FIXATION AND NITROGEN TRANSFER IN BIRDSFOOT-TREFOIL ORCHARDGRASS COMMUNITIES

Birdsfoot trefoil (Lotus corniculatus L.) is an important Perennial fo rage legume used primarily for pasture. Despite its traditional usage as a source of nitrogen for cropping systems, little information is av ailable on the amounts of atmospheric dinitrogen (N2) that birdsfoot t refoil fixes or transfers to an associated grass during long-term stan ds. Field research was undertaken to compare N2 fixation and N transfe r potentials of three birdsfoot trefoil cultivars and one experimental line (hereafter referred to collectively as the birdsfoot trefoil cul tivars). These were seeded in binary mixtures with orchardgrass (Dacty lis glomerata L.). Dinitrogen fixation and N transfer were estimated b y N-15 isotope dilution, using orchardgrass pure stands as a reference . Over the 2-yr study, percentage legume N derived from fixation range d from 93 to 95% among the birdsfoot trefoil cultivars. Dinitrogen fix ation usually did not differ among cultivars within harvests. Total-se ason fixed-N yields among cultivars for the two years ranged from 90 t o 138 kg ha-1. Percentage orchardgrass N derived from N2 fixation and N transfer ranged from 8 to 46%. Nitrogen transfer did not differ amon g birdsfoot trefoil cultivars at any harvest. Total-season transferred -N yields ranged from 4 to 42 kg ha-1, with no differences among culti vars. Under the conditions of this study, the birdsfoot trefoil cultiv ars tested generally did not differ in their abilities to fix atmosphe ric N2 or to transfer fixed N to associated orchardgrass.