Author
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Staley, Thomas |
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Voigt, Paul |
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Submitted to: Soil Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/21/2000 Publication Date: 7/16/2000 Citation: Staley, T.E., Voigt, P.W. 2000. Methodological considerations for elucidating low-level liming effects on white clover symbiosis establishment in an acidic soil model system. Soil Science 165:567-577. Interpretive Summary: Establishment of nitrogen-fixing forage legumes on stressful soils is a serious problem for livestock producers in the south and east. Using a laboratory model system, it was shown that increasing soil pH by liming from 4.5 to only 4.9 dramatically increased white clover nodulation by rhizobia. It was also shown that high populations of rhizobia in the soil can overcome nodulation reduction due to soil acidity. It was concluded that the development of rhizobial strains better able to survive soil acidity-related factors would result in legume-based pastures that would persist Longer at less expense to the producers. Technical Abstract: As acidic soils limit the establishment, growth and persistence of forage legumes, new information on symbiosis development in these soils, particularly during its early stages, will likely contribute to the solution of this worldwide problem. A previously described, laboratory model system was used to determine the effects of low-level liming rates (pHw 4.54 - 4.94) and decadal rhizobial (Rhizobium leguninosarum bv. trifolii) inoculation levels, of both fresh and re-wet soil, on the growth and nodulation of Huia white clover (Trifolium repens L.). Plant parameters (shoot mass, shoot N uptake and root mass) were generally unaffected by liming at any of the inoculation levels at Cut 1 (2 weeks) in both soils, whereas most of these parameters were positively affected by liming at all inoculation levels at Cut 2 (4 weeks), especially in the fresh soil. Positive lime rate effects on nodulation were found at both cuts in both soils, but almost exclusively at the highest (5 x 103 CFU g-1 dry soil) inoculation level. Thus, the interactive effects of liming and rhizobial population on nodulation were demonstrated. Growth rates of asymbiotically-grown roots, determined by short-term (hours) assays in soil-over-agar, paralleled the root mass responses to liming in the soil model system. Rhizobial viability, assessed in soil solutions extracted from the limed soils, decreased by about one log after only 21 hours. Overall, these results suggest that, although seedling root growth, and likely rhizobial viability, are compromised within hours after planting and inoculation by soil acidity-related chemical factors, maintenance of a threshold level of viable rhizobia can lead to improved nodulation of white clover even at very low soil pH values. |
