Asymbiotic nitrogen fixation by a free N2-fixing strain has been followed in biofermentor during straw-sawdust mixtures composting added up or not in glucose. The physico-chemical and microbiological analyses have placed in prominent position different phases of microbiological activity during aerobic decomposition of these wastes, but especially proved the primordial part of a soluble carbon compound such as glucose, on the asymbiotic nitrogen fixation. In fact, with glucose, three nitrogen fixation phases have been observed. The first one, occured since the first days of composting, seems to be due to microorganisms both N2-fixers and cellulolytic. The nitrogen enrichment of the medium has reached value of 7.86g Kg-1 initial dry matter(D.Mi). The two other phases have appeared on day 42 and day 97 with nitrogen gains of the medium of 2.37 and 1.29g Kg-1DMi, and would be due as to Azotobacter. Without glucose, the nitrogen fixation which has only intervened on day 99 of fermentation with a N2 enrichment of the medium of 2.96g Kg-1D.Mi seems to be due to Azotobacter: During this experimentation, no phosphorus, an element necessary to free N2-fixers was added. However, a relatively important nitrogen fixation has been registered and no effect of deficiency of phosphorus has been observed in the free living N2-fixers.

P F Fottrell

Papers

Recent advances in biological nitrogen fixation