Studies on the mechanism of biological nitrogen fixation Part IV. Nitrogen fixation by the mixed microflora of the soil in presence of the acid products of anaerobic decomposition of carbohydrates

Abstract

(1) When fairly large quantities of mixed calcium salts of organic acids (obtained after anaerobic fermentation of sugar) are added to a mineral medium containing soil, only a small portion of the added organic matter is used up in the course of 12 days. The quantity of nitrogen fixed, though small, is proportionately high when compared with the carbon utilised. (2) When the acid products are added directly to the mineral medium, (without neutralisation) there is fairly rapid utilisation of carbon. There is also correspondingly greater fixation of nitrogen. (3) When varying quantities of acid products are added together with the sugar, the best return of nitrogen for the carbon utilised is obtained when the mixed calcium salts are of the order of 20 mg. of the organic carbon to 10 g. of the soil. (4) When the mixed calcium salts are added after the sugar is completely used up, there is enhanced fixation of nitrogen, the ratio of fixed nitrogen to the carbon utilised being as 1:20. (5) Trials with two different types of soil (one, a red sandy loam, and the other, an alkali soil) showed that the mixed calcium salts are used nearly to the same extent in both the cases. The corresponding fixation is also similar, yielding ratios ranging between 1:13 and 1:17. (6) The significance of the foregoing observations and their possible extension to field practice are discussed.