
TY  - JOUR
A1  - Unkovich, MJ 
A1  - Pate, JS 
A1  - Sanford, P 
A1  - Armstrong, EL 
T1  - Potential precision of the &#948;<sup>15</sup>N natural abundance method in field estimates of nitrogen fixation by crop and pasture legumes in south-west Australia
JF  - Australian Journal of Agricultural Research
JO  - Aust. J.  Agric. Res.
Y1  - 1994
VL  - 45
IS  - 1
SP  - 119
EP  - 132
KW  - measurement of N2 fixation;crop and pasture legumes;15N natural abundance;precision of measurement
UR  - https://doi.org/10.1071/AR9940119 
N2  - Precision of estimation of the proportion of legume N derived from N2 fixation (%Ndfa) was assessed in relation to subterranean clover (Trifolium subterraneum L.) pastures and crops of pea (Pisum sativum L.) and lupin (Lupinus angustifolius L.) under south-west Australian conditions. By using a standardized 10-point sampling procedure of paired sampling of legume and reference plant and reference plant 15N natural abundance (S15N) values in the range from +2.9 to +4. 0%o, %Ndfa of sample crops of lupin and field pea and a clover pasture were assessed with respective precisions of 93¦ O.6%, 76¦ 2.4% and 91¦1.3% (¦ s.e., n = 10). Effects on S15N due to isotope discrimination during fixation and subsequent distribution of N by the three study legumes were studied using sand-cultured, fully symbiotic plant material. The resulting S15N data (B values) showed consistently more negative values for shoots than roots (all species), no significant effects of cultivar on B values (all species), a marked effect of rhizobial strain on B value (subclover) and a tendency for B values to fall with plant age (pea and lupin). The likely magnitude of errors in %Ndfa estimates due to incorrect choice of B value was indicated. By using data for reference plant S15N values from field surveys and previously assessed error factors in mass spectrometric measurement of S15N, precision of estimation of %Ndfa by using bulked material from the 10-point field sampling procedure was predicted for situations ranging from where a legume was obtaining only minimal amounts (10%) through to the bulk (90%) of its N by atmospheric fixation. 
ER  -

