Influence of single applications of nitrogen on white clover nitrogen fixation in autumn and winter dairy pastures in south-west Victoria, Australia

Abstract

Abstract:Effects of nitrogen (N) (0, 15, 30, 45 and 60kg N ha^-1) applied at five different times during autumn and early winter on the N fixation of Trifolium repens L. (white clover) in Lolium perenne L. (perennial ryegrass) white clover pastures were examined (Experiment 1). Effects of applying different N fertilisers (e.g. urea and ammonium nitrate) at 45kg N ha^-1 in autumn, with and without phosphorus (P), potassium (K) and sulphur (S) on N fixation were also tested (Experiment 2). In Experiment 1, percentage N derived from the atmosphere (percent Ndfa) by white clover varied between 87% and 91% in the period after (24 to 36 days) N application. Increasing rates of N and time of application did not influence percent Ndfa. The amount of N fixed by white clover ranged from 0.8 to 3.7kg N ha^-1 in the period after N application. Increasing rates of applied N produced a significant (P < 0.05) linear increase in the amount N fixed. In Experiment 2, percent Ndfa and amount of N fixed (1.9 to 4.1kg N ha^-1) were unaffected by different N fertilisers, with and without P, K and S, in the period after (37 days) fertiliser application. For both experiments, fertiliser N increased dry matter yield while having no effect on white clover composition. It is concluded that single applications of N during the autumn and early winter benefit pasture growth without adversely affecting white clover N fixation or clover composition. This finding, however, will require further investigation.

Keywords: Australia; autumn; botany; dry matter yield; Lolium perenne; nitrogen; nitrogen fixation; pastures; perennial ryegrass; species composition; Trifolium repens; white clover; winter; yield; ammonia; fertilization; nitrate; pasture; phosphorus; potassium; ryegrass; victoria

African Journal of Range & Forage Science, Vol. 15(1 & 2), pp. 1–6