Assessment of the relative uptake of added and indigenous soil nitrogen by nodulated legumes and reference plants in the 15N dilution measurement of N2 fixation: Derivation of method |
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| Authors: | SF Ledgard R Morton JR Freney FJ Bergersen JR Simpson |
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| Institution: | 1. Department of Environmental Biology, Australian National University, CanberraAustralia;1. Division of Mathematics and Statistics, C.S.I.R.O., Canberra, Australia;2. Division of Plant Industry, C.S.I.R.O., Canberra, Australia |
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| Abstract: | Current methods for measuring N2 fixation by nodulated legumes involve the addition of small amounts of 15N-labelled plant-available N compounds to soil so that plant N derived from the soil may be identified. All such 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 labelled 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 readilly-obtainable plant N measurements. |
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