Abstract
The investigations were made into humus contained in Tyulin's so-called G1 (i. e. the organo-mineral complex : the fraction, below 2μ, isolated by Gedroiz's method) of paddy soil. The soils used were taken from the degraded paddy field and its neighboring normal paddy field respectively. The results obtained and the discussion are as follows. The total amount of humus in G_1 is larger in the degraded than in the normal soil, and a proportion of "easily-soluble humus"-which comes to be dispersed in n/100 NaOH solution after treating the moist soil with n/100 HCl-to it is also higher in the former than in the latter. Moreover, in the degraded, the proportion of H_1 (Tyulin's 1st humate fraction) to "easily-soluble humus" is much higher than that of H_2 (Tyulin's 2nd humate fraction). These results lead to the assumption that in the degraded paddy soil a considerable proportion of humus in G_1 is either present in a free form or associated loosely with the surface of colloids. (See Table 1 and 2). In all samples, humic acids of which "easily-soluble humus" is composed are higher in rotted products than in true humic acids (after K. Simon). These humic acids are presumed to be U. Springer's brown humic acid (F. Q.=3.0) from their colourcurves. (See Fig. 1). In view of our assumption in a previous paper that "easily decomposable organic matter" of paddy soil must be contained in "easily-soluble humus", it is highly probable that a larger amount of "easily decomposable organic matter" is accumulated in G_1 of the degraded than in that of the normal soil. The determination of humic acids in "non-easily-soluble humus" (after U. Springer's method) showed that the proportion of the grey humic acid to "non-easily-solucle humus" of G_1 is far lower in the degraded than in the normal. (See Table 3 and Fig. 2). These results suggest that in the degraded paddy soil humification does not occur so progressively as in the normal, since the grey humic acid is regarded as being most humified among humic acids according to U. Springer, E. Welte et al. This suggestion seems to be consistent with the facts, also, that a higher proportion of humus, especially "easily-soluble humus" of less humified, is found in G_1 of the degraded than in that of the normal. Concerning this problem, it still remains to be solved why the progress of humification is more retarded in the degraded paddy soil than in the normal.
