An appraisal of recent field measurements of symbiotic N 2 fixation by annual legumes

In this paper we review both the methods for estimating N 2 fixation and the quantity of N 2 fixed by annual crop legumes. Available data on the N difference method for estimating N 2 fixation reveal it to be unreliable. Although we advocate the use of isotope-based techniques their limitations nece...

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Bibliographic Details
Published inField crops research Vol. 65; no. 2; pp. 211 - 228
Main Authors Unkovich, Murray J., Pate, John S.
Format Journal Article
LanguageEnglish
Published Elsevier B.V 01.03.2000
Subjects
15N
Acetylene reduction
Legume roots
Mineral N
Ureides
15N
Mineral N
Ureides
Acetylene reduction
Legume roots
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Summary:In this paper we review both the methods for estimating N 2 fixation and the quantity of N 2 fixed by annual crop legumes. Available data on the N difference method for estimating N 2 fixation reveal it to be unreliable. Although we advocate the use of isotope-based techniques their limitations necessitate the simultaneous collection of supporting data in the form of nodulation status, soil mineral N availability, and N yields of non-N 2 fixers. To improve confidence in isotopic techniques for estimating N 2 fixation differences in the form and function of plant roots are highlighted as critical areas for future research, as is a greater understanding of the total N contained in legume roots. A survey of the quantities of N 2 fixed reveals the principal crop legumes to be ranked in the following descending order: soybean, lupin, field pea, faba bean, common bean, lentil, and chickpea.
ISSN:0378-4290
1872-6852
DOI:10.1016/S0378-4290(99)00088-X