Assessment of the relative uptake of added and indigenous soil nitrogen by nodulated legumes and reference plants in the nitrogen 15 dilution measurement of nitrogen fixation derivation of method

Ledgard, S.F.; Morton, R.; Freney, J.R.; Bergersen, F.J.; Simpson, J.R.

Soil Biology and Biochemistry 17(3): 317-322


ISSN/ISBN: 0038-0717
Accession: 004788652

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Current methods for measuring N2 fixation by nodulated legumes involve the addition of small amounts of 15N-labeled plant-available N compounds to soil so that plant N derived from the soil may be identified. All methods assume that the proportions of added N and indigenous soil N assimilated by N2-fixing and non-fixing plants grown in the same soil are the same, irrespective of the amount of soil N assimilated. The development of a method for assessing these proportions is described. Nodulated legumes and reference plants are grown in soils receiving none or one rate of addition of labeled N compound containing several (two or more) concentrations of 15N. The proportions of added and indigenous N assimilated, are determined from the intercepts and slopes of regression lines relating isotopic composition of plant N to that of added N, together with some other readily-obtainable plant N measurements.