Assessment of N 2 fixation by Casuarina equisetifolia inoculated with Frankia ORS021001 using 15N methods

Abstract

Casuarina equisetifolia seedlings, uninoculated or inoculated with Frankia strain ORS021001 were grown for 4.5 months in pouches, then transplanted into 1 m 3 concrete containers forming 1 m 2 microplots. Trees were harvested 6.5 months later when they were 11 months old. N 2 fixation was measured using three methods of assessment: the direct isotopic method, the A-value method and the difference method. Estimations of N 2 fixation during the 6.5 months following transplantation were respectively 3.27, 2.31 and 3.07g N 2 per tree. From these values it was calculated that about 40–60 kg N 2 would be fixed per hectare in a year at normal densities of 10,000 trees ha −1. The results of this experiment confirm that Frankia strain ORS021001 can be confidently recommended to inoculate casuarinas in the field. Means to improve nodulation and subsequently N 2 fixation by casuarinas are discussed.