Biology and Fertility of Soils

, Volume 47, Issue 4, pp 377–385 | Cite as

Symbiotic N2 fixation and nitrate utilisation in irrigated lucerne (Medicago sativa) systems

  • Huimin Yang
  • Murray Unkovich
  • Ann McNeill
  • Xianzhi Wang
Original Paper


Symbiotic N2 fixation by lucerne (Medicago sativa) has capacity to provide significant inputs of N to agro-ecosystems, and the species has also been shown to scavenge soil mineral N and thus act as a sink for excess reactive N. The balance between these two N cycle processes was investigated in an extensive irrigated lucerne growing region where nitrate contamination of groundwater has been reported. We sampled 18 permanent pure lucerne stands under irrigation for standing dry matter, total shoot N, and N2 fixation using 15N natural abundance along with activity of the inducible enzyme nitrate reductase as indicators of use of soil NO3 by lucerne. On average 65% of lucerne N was obtained from symbiotic N2 fixation. Converting standing dry matter estimates to annual N2 fixation amounts we calculated average N2 fixation of 311 kg N/ha, including N in roots and nodules. Uptake of N from soil by lucerne was calculated to be 181 kg N/ha/year. We were not able to identify the source of this soil mineral N, although nitrate reductase activity of lucerne was higher than that of non-N2 fixing species examined.


Nitrate reductase Nitrogen cycle Alfalfa N2 fixation 15N natural abundance 


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Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  • Huimin Yang
    • 1
  • Murray Unkovich
    • 2
  • Ann McNeill
    • 2
  • Xianzhi Wang
    • 1
  1. 1.Key Laboratory of Grassland Agro-Ecosystems of Ministry of Agriculture, School of Pastoral Agriculture Science and TechnologyLanzhou UniversityLanzhouChina
  2. 2.School of Agriculture, Food and WineThe University of AdelaideAdelaideAustralia

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