Nitrogen fixation by nine white clover cultivars in grazed pasture, as affected by nitrogen fertilization

Abstract

Forage production and N2 fixation were determined for nine cultivars of white clover (Trifolium repens L.) grown with perennial ryegrass (Lolium perenne L.) and receiving nitrogen (N) fertilizer at either 0 or 390 kg N ha-1 yr-1. The site was grazed by sheep at 3 or 6 (in winter and summer) week intervals and N fertilizer was applied at 30 kg N ha-1 after each grazing. Annual white clover production showed a 2-fold variation between cultivars and was positively correlated with total pasture production in the 0 N treatment. Nitrogen fertilizer application increased average total pasture dry matter (DM) production from 12830 to 16010 kg ha-1 yr-1, but decreased average white clover production from 3600 to 2970 kg DM ha-1 yr-1.