IN INOCULANTS Nodulaid - 17th International Nitrogen Fixation ...

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17 th International Congress on Nitrogen Fixation Fremantle, Western Australia 27 November – 1 December 2011 Session Details: Tuesday 29 November 2011 Concurrent Session 7 – Field Applications III 1600 - 1720 Authors: Elizabeth Drew 1 , Victor Sadras 1,2 , Lachlan Lake 1 , Matthew Denton 2 & Ross Ballard 1 1 Plant and Soil Health, South Australian Research and Development Institute, GPO Box 397, Adelaide, SA, 5001, Australia. 2. School of Agriculture, Food and Wine, The University of Adelaide, Glen Osmond, SA, 5064, Australia Presentation Title: Impacts of pea genotype and soil rhizobia on N2-fixation by field pea Presentation Time: 1600 – 1620 Enhancing the fixed N contribution from legumes into agricultural systems will become increasingly important as higher N fertiliser costs erode farm profitability. This paper examines factors affecting the N2-fixation potential of field pea (Pisum sativum). Having previously shown that about 70% of southern Australian cropping systems with a history of pea cultivation contain adequate numbers of rhizobia for prompt nodulation (>100 rhizobia per g soil), recent efforts have been directed at understanding the intrinsic compatibility (N2-fixation capacity) of pea genotypes with soil rhizobia. Contributions of fixed N by different pea genotypes have also been quantified in the field. The greenhouse assessment of commercial pea cultivars and advanced breeding lines with soil rhzobia included material with diverse maturity times and growth habits. Effective symbioses formed with most communities of soil rhizobia, but some variation occurred between pea genotypes. For example, the symbiotic performance of cv. Kaspa was on average 10% lower than that of cv. Parafield (85%) when nitrogen fixation resulting from 82 soil inoculants was compared to the commercial inoculant strain (SU303). When five pea genotypes were grown in the field, differences were measured in nodulation pattern and partitioning of dry matter, which contributed to large differences in N benefit. Pea genotypes were sown with and without N fertiliser at Roseworthy SA and were reliant on soil rhizobia for nodulation. Nodule number and distribution on the roots eight weeks after sowing varied significantly with pea genotype and nitrogen treatment. Nodule mass/g root was weakly (R 2 =0.17) but significantly (P
17 th International Congress on Nitrogen Fixation Fremantle, Western Australia 27 November – 1 December 2011 Session Details: Tuesday 29 November 2011 Concurrent Session 7 – Field Applications III 1600 - 1720 Authors: Julie Grossman 1 , Nape Mothapo 1 , Mary Parr 1 , Malik Oliver 1 1 North Carolina State University, Department of Soil Science, Raleigh, North Carolina, 27695. Presentation Title: Effect of cover crop planting history on Rhizobium leguminosarum ecology in organic farming systems Presentation Time: 1620 – 1640 Biological nitrogen fixation (BNF) is a major contributor of nitrogen to certified organic farming systems in the United States (U.S.), with presence of effective rhizobia strains being essential for optimal nodulation of legume cover crops and green manures. Organic farmers have particular interest in the winter annual cover crop species hairy vetch (HV; Vicia villosa Roth). Our recent work in the Southeastern U.S. shows V. villosa to have high biomass production and BNF capacity, with many varieties producing over 200 kg N ha -1 , and more than 170 kg N ha -1 derived from BNF. In this study we determined the impact of past hairy vetch cultivation on resident Rhizobium leguminosarum biovar viciae (Rlv) populations. Organic farm soils with and without history of HV cultivation were used to assess effect of planting history on nodulation of ten HV trap-host genotypes and diversity of Rlv. Paired soils from each field type were collected from three organic farms across North Carolina. Plants were inoculated with soil dilutions from the six fields and used to trap Rlv in a growth chamber. V. villosa inoculated with HV+ soil dilutions had 60% more nodules with 70% greater total mass than HV- treatments. Two of three HV+ soils produced greater plant biomass and plant tissue N than those inoculated with soil dilutions from HV- fields, suggesting improved BNF. Molecular analysis of the 473 Rlv isolates using BOX-PCR produced more than 35 genetic groupings across the three sites, and indicated that rhizobia diversity was most impacted by site, followed by hairy vetch field history. Results suggest that hairy vetch cultivation appears to increase population size of resident Rlv capable of nodulation and BNF with hairy vetch cover crops. Current work is underway to quantify Rlv populations in each field type using qPCR and Most Probable Number methodologies. 53 2011
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