Studies on the anaerobic decomposition of plant materials: The anaerobic decomposition of rice straw (Oryza sativa).

THE aerobic decomposition of plant materials has in recent years attracted much attention, on account of its importance in the formation of synthetic manure, in the decomposition of soil organic matter, in the purification of sewage and trade wastes, in the decay of wood etc., but comparatively little is known regarding the course and rate of decomposition under anaerobic an,d partially aerobic conditions. Tenney and Waksman [1930] have reported some data in this connection and a certain amount of work has been done in regard to the changes in organic matter in marshy and peaty soils, generally associated with such conditions. While the agricultural importance of such soils is comparatively limited, in other cases anaerobic and semi-aerobic conditions have played a significant role in increasing crop production and have been objects specially aimed at in the system of cultivation, e.g. in the production of rice under swamp or waterlogged conditions as practised in most parts of India and China and to an increasing extent in Burma. The biochemistry of the changes in organic matter and other constituents in such soils has been examined by Nagaoka [1905], Daikuhara and Imaseki [1907], Harrison and Jyer [1913; 1914; 1915; 1916; 1919; 1920], Panganiban [1923], Subrahmanyan [1927; 1929; Subrahmanyan and Sreenivasan, 1934], Itano and Arakawa [1927; 1932], Metzger [1929; Metzger and Janssen, 1928], Joachim and Kandiah [1929], Misu and Shimohira [1929], Bartholomew [1929], Robinson [1930], Osugi et al. [1931; 1932] and others. But their work has been done mostly under the semi-aerobic conditions of the waterlogged soil and no detailed study of the decomposition of organic matter under strictly anaerobic conditions has been reported. Data under such conditions, it was thought, might serve not only for purposes of comparison, but might also help in the interpretation of the results obtained already under water-logged conditions. The object of the experiments reported in this and succeeding papers was to examine in detail the course of anaerobic decomposition of a variety of plant materials by themselves and in admixture with soil, as compared with the course of aerobic decomposition on. the one hand and with the decomposition under water-logged or swamp soil conditions, on the other. Recently much work has been reported on the anaerobic digestion of sewage and trade wastes, with special reference to securing the maximum evolution of combustible gases [cf. Whitehead and O'Shaughnessy, 1931; Adeney, 1932; Heukelekian, 1933; Rudolfs, 1932; Rudolfs and Heukelekian, 1932; Rudolfs and Setter, 1932; Buswell and Boruff, 1932; Larson et al. 1934]. But it should be noted that the conditions influencing the decomposition of trade wastes or sewage, where the concentration of the dissolved or suspended matter is comparatively low, may vary markedly from those controlling the decomposition of