
TY  - JOUR
A1  - Doughton, JA 
A1  - Saffigna, PG 
A1  - Vallis, I 
A1  - Mayer, RJ 
T1  - Nitrogen fixation in chickpea. II. Comparison of <sup>15</sup>N enrichment and <sup>15</sup>N natural abundance methods for estimating nitrogen fixation
JF  - Australian Journal of Agricultural Research
JO  - Aust. J.  Agric. Res.
Y1  - 1995
VL  - 46
IS  - 1
SP  - 225
EP  - 236
KW  - biological nitrogen fixation;15N natural abundance;15N enrichment;chickpea;15N methodology;legumes
UR  - https://doi.org/10.1071/AR9950225 
N2  - 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. 
ER  -

