Abstract
The proportional contribution of atmospheric N2 to the N nutrition of lupin (P atm) was estimated in a field experiment following addition of NH4Cl of KNO3 to unconfined microplots (1.5 m2) at 2.5 g N m-2 (10 atom% 15N). The integrated 15N enrichment, or ‘mean pool abundance’, of nitrate extracted from 0- to 15-cm samples taken under the lupin crop on eight occasion between 28 and 190 days after sowing was used as the reference criterion to estimate P atm by the 15N-isotope dilution technique. Estimates of P atm were similar to those obtained using canola as a non-fixing reference plant, but were higher than estimates obtained using a yield-dependent model. Use of ‘mean pool abundance’ obviates the need for a non-fixing reference plant, and the frequent sampling and isotope-ratio analysis of the legume biomass required with the yield-dependent model is unnecessary. However, further work is needed to validate a sampling strategy commensurate with the growth of the legume roots.
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Chalk, P.M., Smith, C.J., Hopmans, P. et al. A yield-independent, 15N-isotope dilution method to estimate legume symbiotic dependence without a non-N2-fixing reference plant. Biol Fertil Soils 23, 196–199 (1996). https://doi.org/10.1007/BF00336063
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DOI: https://doi.org/10.1007/BF00336063