Abstract

An important and economic source of nitrogen for Mediterranean crop and forage systems arises from symbiotic nitrogen fixation, which contributes also to a high environmental protection and sustainability.
This papers refers on the quantification of nitrogen fixation in sweetvetch, by the isotopic dilution and nitrogen balance methods. In addition, the effect of sweetvetch inoculation with a Sardinian strain of Rhizobium sullae was evaluated against an uninoculated treatment.
The potential of nitrogen fixation in sweetvetch, estimated by the isotopic dilution method, resulted high, reaching 180 kg ha^-1 of nitrogen fixed in the biennium. The nitrogen balance method underestimated the nitrogen fixation compared to the isotopic dilution.
Very low differences between inoculated and uninoculated sweetvetch were due to a presence of resident rhizobia in the soil. This result outlines the need of evaluating where inoculation is necessary or useless.

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