Use of isotope dilution to measure nitrogen fixation associated with the roots of sorghum and millet genotypes

1573-5036

Vermiculite ; Millet ; 15N Nitrogen fixation (associative) ; Non-exchangeable-N

Springer Online Journal Archives 1860-2000

Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Summary Genotypes of sorghum and millet have previously been found to have different amounts of root-associated acetylene reduction activity. Isotope dilution experiments using15N have been carried out to evaluate the amount of nitrogen fixed by bacteria which is incorporated into the different genotypes when grown in vermiculite in the glasshouse. Isotope dilution result indicated that the content of shoot nitrogen derived from biological nitrogen fixation varied by up to 27% between sorghum genotypes and 17% between millet genotypes. Considerable isotope dilution also resulted from uptake of non-exchangeable-N (as NH 4 + ) in the vermiculite. It is possible that the genotypic differences in isotope dilution may reflect differences in the ability of plants to take up non-exchangeable-N, and that vermicultite is therefore an unsuitable growth medium for such studies.

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