N-2-FIXATION, NODULE EFFICIENCY AND BIOMASS ACCUMULATION AFTER 2 YEARS IN 3 CHILEAN LEGUME TREES AND TAGASASTE CHAMAECYTISUS-PROLIFERUS SUBSP PALMENSIS

Initial results of a long-term field experiment are presented for the above and below-ground biomass accumulation after two years, as well a s root nodulation, nodule efficiency (g N fixed/g nodules) and biologi cal N-2 fixation (using the N-15 isotope dilution method) of four N-2- fixing tree species (NFTs) grown in the subhumid mediterranean-climate zone of central Chile. Two non-legume tree species, Fraxinus excelsio r and Schinus polygamus, were used as reference plants for the isotope dilution calculations. Over two years, Tagasaste (Chamaecytisus proli ferus subsp. palmensis, a Papilionoideae from the Canary Islands), pro duced 10 to 20 times more biomass than the other three NFTS (Acacia ca ven, Prosopis alba and Fl chilensis); all Mimosoideae native to Chile) , and nodulation and nitrogen fixed were an order of magnitude higher as well. At the end of the second year, the percentage of N derived fr om N-2 fixation (%Ndfa) in Tagasate averaged 85.6, equivalent to ca. 4 9.1 g N fixed per tree. For all four NFTs, however, %Ndfa, nodule effi ciency, and total N accumulation varied from one year to the next; cau tion is thus required in interpreting or predicting NFT performance ov er the long term, even if Tagasaste can already be considered a highly promising NET for central Chile.