ON THE MASS-CULTURING OF A NITROGEN- FIXING BLUE-GREEN ALGA, TOLYPOTHRIX TENUIS

It has been reported by the present author (1, 2) and later by ALLEN (3) that the growth of rice plant was improved, at least in small scale experiments, by inoculating nitrogen-fixing blue-green algae in the nutrient medium. In order to examine the possibility of application of this method to agricultural practice, large scale tests of the effect of these organisms on the crop yield of rice were carried out, under the direction of the present author, during the period from 1951 to 1956 at eleven experimental farms in various parts of this country (4, 5). In these experiments, Tolypothrix tenuis, a markedly potent nitrogen-fixing blue-green alga isolated from mud of a rice field in Borneo (6), was used as the test organism. By preliminary experiments it was found that in order to apply the alga successfully to the paddy fields, it should be sown to the field-water at the beginning of the rice-planting season which is usually between June and July in Japan, and that the adequate quantity of seeding was about 1-5 kg (dry weight) of alga per acre. The practical problem was, therefore, how to obtain in mass the viable alga for seeding within such a short period of early summer. The difficulty in growing Tolypothrix on a large scale lies in the fact that it is liable to be contaminated and eventually overcome by other common microalgae, such as Chlorella and Scenedesmus, unless proper measures are taken to protect the culture from these hardy organisms. The purpose of this paper is to describe the methods of mass culture which proved to be feasible in obtainig a large quantity of Tolypothrix to be used as seeding material for the inoculation of the paddy field.