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RESEARCH ARTICLE

Factors associated with biological nitrogen fixation in dairy pastures in south-western Victoria

Penny A. Riffkin, Paul E. Quigley, Gavin A. Kearney, Fiona J. Cameron, Robert R. Gault, Mark B. Peoples and Janice E. Thies

Australian Journal of Agricultural Research 50(2) 261 - 272
Published: 1999

Abstract

A survey of 71 sites was conducted in the dairying districts of south-western Victoria in October 1994 to determine factors associated with nitrogen (N) fixation in white clover based pastures. Twenty-eight factors (environmental, microbiological, management, soil, and pasture) were considered in relation to 2 indicators of N fixation by white clover, %Ndfa (percentage of total plant N derived from the atmosphere, as determined by the 15N natural abundance method) and kg of N fixed per tonne herbage dry matter (legume and non-legume). On light-textured soils (sandy loams), soil potassium, rhizobia numbers, total soil N, and density of the nematode Pratylenchus sp. accounted for 72% of variation in %Ndfa. On medium-textured soils (clay loams), crude protein of perennial ryegrass and plant-available phosphorus in the soil accounted for 30% of variation in %Ndfa. The amount of N fixed was influenced by different factors, again depending on soil texture. Soil chemical properties accounted for 31% variation on the medium-textured soils with nematode density, pasture quality, and soil chemical properties accounting for 77% of variation on light-textured soils. Amounts of N fixed per tonne herbage dry matter produced averaged 8.2 kg on the light-textured soils and 7.3 kg on the medium-textured soils. Average %Ndfa values were 67% and 60% on light- and medium-textured soils, respectively. Effects of soil texture on N fixation were attributed to the different cation exchange and water-holding capacities of the soils and highlight the importance of considering soil type in N fixation studies.

Keywords: 15N natural abundance, nematodes, phosphorus, rhizobia, potassium, white clover, Rhizobium leguminosarum bv. trifolii, Trifolium repens, N fixation.

https://doi.org/10.1071/A98035

© CSIRO 1999

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