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.

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The investigation shows that when ammonium sulphate or oil cake was applied to cropped rice soils 4 weeks after transplantation, a considerable amount of the added nitrogen was lost as gas. This loss, however, was less than the loss that took place when the crop was absent. Placement of ammonium sulphate 3 in. below the soil surface reduced the loss of nitrogen, but did not significantly increase the crop yield. Gases evolved from cropped rice soils, whether unmanured or treated with ammonium sulphate, were free from hydrogen and contained practically no methane, while those formed in the uncropped soil under similar treatments contained large volumes of these two gases.