Herbage yield and nitrogen-fixation in a triple-species mixed sward of white clover, lotus and fescue

Abstract

The herbage yield and N, fixed (based on 15N isotope dilution) in a three-species mixed sward [white clover ( Trifolium repens L.). birdsfoot trefoil ( Lotta corniculatus L.) and fescue (Frsluca uranjinacea Schrcb)] were evaluated over a 2 yr growth cycle (1986 and 1987). Three harvests were made in each year. The herbage yield of white clover was significantly higher than that of birdsfoot trefoil in only the first two cuts, with birdsfool trefoil accounting for 86% of the total legume herbage yield in the remaining four harvests. For both legume species the proportion of the aboveground N derived from atmospheric N 2 (% Ndfa) fluctuated little over the different harvests. The 2-ycar averages were. 88 and 91% Ndfa, for while clover and birdsfoot trefoil, respectively. The large fluctuations in the amounts of N; fixed (Ndfa) across harvests and between the legume species reflected differences in herbage yield. In 1986, both legumes contribued almost equally to the ca 130 kg N ha 1 fixed, compared to 1987. when white clover contributed only 5% of ihe 46 kg N ha ' fixed in the lust two harvests. The better persistence of birdsfoot trefoil than while clover was therefore not only reflected in higher yields, but also, in greater N, fixed. Nitrogen fertilisation had a differential ell'ect on N 2 fixation in the two legumes, with the application of 10 instead of 2 kg N ha 1 decreasing N 2 fixation in while clover, but not birdsfool trefoil.