
%0 Journal Article
%A Doughton, JA 
%A Saffigna, PG 
%A Vallis, I 
%A Mayer, RJ 
%T Nitrogen fixation in chickpea. II. Comparison of <sup>15</sup>N enrichment and <sup>15</sup>N natural abundance methods for estimating nitrogen fixation
%J Australian Journal of Agricultural Research
%D 1995/02/01
%V 46
%N 1
%P 225-236
%K biological nitrogen fixation;15N natural abundance;15N enrichment;chickpea;15N methodology;legumes
%R https://doi.org/10.1071/AR9950225
%U https://www.publish.csiro.au/paper/AR9950225 
%X The 15N enrichment and 15N natural abundance methods for estimating N2 fixation in chickpea were compared over a range of soil NO3-N levels at crop establishment varying from 10 to 326 kg N/ha (0-120 cm depth). Barley was used as a non-N2 fixing control crop. Both methods estimated reduced N2 fixation as soil NO3-N levels at crop establishment increased. Similar estimates of % N2 fixation were obtained at high values, but at low values the enrichment method gave lower estimates, some of which were negative. The 15N natural abundance method provided realistic estimates of % N2 fixation across all soil N03-N levels at crop establishment. An asymptotic curve described a close ( R2 = 0.95) relationship between these factors. Standard errors of estimates of means for the 15N natural abundance method remained acceptable and relatively stable over the full range of measurements; however, with the 15N enrichment method they became unacceptably large at low values of % N2 fixation. These large errors may have been partly due to legume and control plants assimilating mineral N of differing 15N enrichment. High mineral N levels associated with low values of % N2 fixation were also shown to reduce reliability of N2 fixation values estimated by the 15N enrichment method. These errors caused potentially greater inaccuracy at low values of % N2 fixation than at high values. To compare N2 fixation means statistically, transformations were necessary to stabilize variance and to impart lower weightings to plots with low values of % N2 fixation. 
