New Zealand Journal of Agricultural Research abstracts

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Symbiotic nitrogen fixation by Trifolium arvense in semi-arid short tussock grasslands

C. C. Boswell

W. L. Lowther

A. J. Rutherford

AgResearch
Invermay Agricultural Centre
Private Bag 50034
Mosgiel 9053, New Zealand
alison.rutherford@agresearch.co.nz

Abstract    We have measured symbiotic N fixation from the widespread annual Trifolium arvense (haresfoot clover) in two studies in the semi-arid zone of the Mackenzie Basin using a ¹⁵N dilution technique over two growing seasons. Apart from one low value of 69%, the percentage of plant nitrogen derived from the atmosphere (%Ndfa) was consistently high in one study at Tomahawk Gully (82–91%). Calculated inputs of symbiotic N fixation from T. arvense was highly variable over the landscape, and between seasons. Calculated symbiotic N fixation inputs on different landscape units in Tomahawk Gully ranged from <0.1 to 3.4 kg N ha^–1 in 2000–01, and from <0.1 to 11.4 kg N ha^–1 in 2001–02 when there was more favourable summer rainfall. Weighted mean rates of N fixation over the whole Tomahawk Gully catchment were 0.5 and 1.6 kg N ha^–1, in the respective seasons. In a study at St Cuthbert, the results were variable in the absence of sulphur (S) fertiliser (56–76%). However, the application of 25 kg ha^–1 of fertiliser S was associated with an increase in the %Ndfa to 89–92% and a 5½-fold increase in the symbiotically fixed N. Application of small amounts of S fertiliser to areas with naturalised legumes within semi-arid grassland offers potential for improving the sustainability of grazed tussock grasslands.

Keywords    haresfoot clover; N fixation; nutrient balance; sulphur; sustainability; Trifolium arvense; tussock grasslands

A04060; Online publication date 2 November 2007; Received 10 June 2004; accepted 16 August 2007

New Zealand Journal of Agricultural Research, 2007, Vol. 50: 511–521
0028–8233/07/5004–0511 © The Royal Society of New Zealand 2007

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