The Role of Blue-Green Algae in Nitrogen Fixation in Rice-Fields

The problem, with which this paper deals, arose out of the observation that in India rice can be grown on the same land for long periods without the addition of manure to the soil (Howard 1924, p. 114). Three distinct periods are distinguishable in Indian rice fields, viz.: (1) Waterlogged period (from transplantation up to harvest time), in which there are a few inches to several feet of water above the soil and which is distinguished by the growth of abundant algae. (2) The dry period, which follows in winter after harvest and during which conditions remain very suitable for microbiology activity. (3) The desiccation period, commencing after winter when the soil temperature frequently exceeds 50° C.