The use of nitrogen-15 natural abundance in white clover (Trifolium repens L.) to determine nitrogen fixation under different management practices

The N-15 natural abundance (delta(15)N) Of white clover (Trifolium repens L,) grown in pasture under different management practices was determined. Plants were split into leaflets, petioles and stolons and the N-15 signature of each tissue was measured. The delta(15)N Of leaflet tissue from plants of two non-N-2-fixing species (Lolium perenne L, and Ranunculus repens L.), growing in close proximity to the sampled T. repens, was also measured. By using T. repens plants grown in the absence of mineral N to provide reference material, the proportion of N derived from N-2 fixation (%Ndfa) in pasture plants was calculated. Within a plot, variation was present in the delta(15)N between the tissues of T. repens. Variation was also present between the same tissues under different management practices. The %Ndfa in the leaf material of T. repens varied from 34% to 100% between the plots. The use of different reference species did not affect the estimate of %Ndfa.