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

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.

Nitrogen fixation in Australian dairy systems: review and prospect

“…The white clover inoculant strain (TA1) was shown to be less persistent in acid soil than five of six other strains in a field comparison on annual clovers (Watkin et al 2000), so this rhizobia may be relatively sensitive to low soil pH. Consistent with this, in the survey of Riffkin et al (1999a) clover dependence on N 2 fixation was negatively correlated with rhizobial numbers on light textured soils (mean pH 4.6) but not on medium textured soils (mean pH 4.9), and the amount of N 2 fixed positively correlated with soil pH on light but not medium textured soils. Although lucerne has been shown to 'select' compatible, effective rhizobia under acid soil conditions (Ballard et al 2003), N 2 fixation will most likely be suboptimal under the typical soil pH of Australian dairy farms.…”

“…trifolii strain TA1 became a benchmark organism, and studies deploying this strain of rhizobia developed into a voluminous literature internationally, but little of this relates to its field performance in N 2 fixation, particularly with the varieties of white clover grown in Australia. As far as I am able to ascertain this has in fact not been examined, although it has been shown to be less effective in N 2 fixation on clovers than a range of other field isolates on several occasions (see Brockwell and Gibson 1968;Riffkin et al 1999a). Under laboratory conditions Gibson et al (1975) found that very few field isolates could match its N 2 -fixing effectiveness.…”

“…The average soil pH on 44 dairy farms across the country in the survey of Gourley et al (2010) was 5.3 (CaCl 2 ), and 4.8 across 71 dairy farms in western Victoria (Riffkin et al 1999a). At such low soil pH rhizobia (Richardson and Simpson 1989) and nodulation (Munns 1965b) are likely to be severely compromised.…”

The impact of nitrogen source and crop rotation on nitrogen mass balances in the Mississippi River Basin

“…Primary sources of variability in the application of the natural-abundance method include selection of reference species and the B values used (e.g., Ho¨gberg 1997, Boddey et al 2000. We measured B values specific to the legume species and varieties that we sampled, but there are problems with applying B values from pot experiments to field measurements of BNF, including differences in BNF efficiency among Rhizobium strains; for instance, we inoculated with one strain, though many different background populations are likely present in the field (Riffkin et al 1999).…”

Comparison ofnifHGene Pools in Soils and Soil Microenvironments with Contrasting Properties

“…In grasslands, plant species may affect microbial biomass and activity (5). Riffkin et al (42) showed that N 2 fixation is influenced by different soil factors, including soil texture. Cejudo and Paneque (9) and Limmer and Drake (29) suggested that the nitrogen status of the soil may also influence N 2 fixation by diazotrophs.…”