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This article in AJ

  1. Vol. 79 No. 5, p. 820-824
    Received: Apr 24, 1986

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Effects of Alfalfa Proportions and Clipping Frequencies on Timothy-Alfalfa Mixtures. II. Nitrogen Fixation and Transfer1

  1. T. C. Ta and
  2. M. A. Faris2



The inclusion of legumes in grass pastures often increases grass yields due to the contribution of the N fixed by the legume to the associated grass. This benefit was evaluated in field experiments under different management conditions at Ottawa, Ontario, Canada, on a Manotick mixed sandy loam soil (Typic Dystrochrett) labeled with I5N. Timothy (Phleum pratense L.) and alfalfa (Medicago sativa L.) were grown in pure stands and in mixtures at two proportions (1:1 and 1:2) and harvested at three alfalfa maturity stages (early, mid-, and late bloom). Nitrogen fixed by alfalfa and N transfer from alfalfa to timothy were calculated from the differences between the isotopic compositions of the two species in mixture and timothy in pure stand. The highest amounts of N in alfalfa shoots originating from N fixed were 192 and 215 kg N ha−1 yr in the first and second year, respectively, when harvested at mid-bloom (four cuts). The inclusion of timothy in alfalfa stands increased the proportion of N fixed by alfalfa. Nitrogen transfer from alfalfa to associated timothy contributed up to 22% (first year) and 30% (second year) of the total N yield of timothy and amounted to up to 13 kg N ha yr . This transfer increased with progressive cuts and with an increased proportion of alfalfa in the mixture. Growing alfalfa in mixture with timothy at a high proportion to timothy is an ideal system for maximum N transfer and for reducing N fertilizer usage.

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