Media type: E-Article Title: Nitrogen fixation in annual and perennial legume-grass mixtures across a fertility gradient Contributor: Schipanski, Meagan E.; Drinkwater, Laurie E. imprint: Springer Science and Business Media LLC, 2012 Published in: Plant and Soil Language: English DOI: 10.1007/s11104-012-1137-3 ISSN: 0032-079X; 1573-5036 Origination: Footnote: