たい肥腐植様物質の性状およびその生成に関する研究
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Although there have been many studies on soil humus since SPRENGEL (1826), the properties and formation of extractable humus-like substance from compost are as yet obscure. Besides, the suitable methods for investigation of them have not been sufficiently established. For the purpose of throwing light upon humus-like substance in compost, the titration curve method of TANFORD was introduced into determining of dissociation radicals in humuslike substance; a procedure of pH-T curve for developing flocculation-beginning point and a refining process of humus-like substance with ion-exchange resins and electrodialysis were deviced. It has been found that there are two fractions in extractable humus-like substance from well-rotted compost. One fraction is soluble, as well as soil true humic acid, in SIMON's pH4 sodium acetate buffer solution, but the other is insoluble in the above solution, even after eliminating sesquioxides to below ca. 0.4 % by treatment with neutral 0.1 M sodium pyrophosphate. Therefore, the former was termed "true humic substance" for avoiding a confusion with soil true humic acid, and the latter "rotted product" arbitrarily by the author. When well-rotted straw compost was treated with mild extractants: e.g., 0.1M sodium pyrophosphate, N/4 sodium oxalate, or dilute solution of sodium hydroxide, true humic substance and fulvic acid were obtained. True humic substance sedimented in the middle room of the PAULI dialyzer after electrodialysis, in state of sol, due to its hydrophilic property. This character was also observed in the case of soil true humic acid, which was soluble in SIMON's pH4 buffer solution. When the residue, from well-rotted compost, after exhaustive extractions of true humic substance with mild extractants was subsequently treated at a temperature of about 100℃ for 1 or 2 hours with 0.5 % sodium hydroxide, rotted product and fulvic acid were extracted. Rotted product was hydrophobic as well as lignin obtained from straw, and it had less amount of acid radicals than true humic substance. Then, rotted product precipitated in the middle room of the dialyser in state of gel after electrodialysis, and it had a higher flocculation-beginning point than true humic substance. When true humic substance was treated, in order to know the degree of its denaturation, at a temperature of 100℃ with 5% sodium hydroxide for 22 hours, humic substance which flocculated by adding mineral acid, was recovered in amount of only 20% of the initial true humic substance, acid soluble compounds being found in amount of about 40%, and the remainder was thought to have been released as gas during treatment. The absorption coefficient of the recovered humic substance became far less than the initial one, but the original property of solubility in SIMON's pH4 buffer solution was still maintained; also the recovered humic substance sedimented in sol state after electrodialysis. So it is evident that the rotted product, which is insoluble in SIMON's pH4 buffer solution, could not be produced by conversion from true humic substance, under the usual conditions of extraction from compost. Interaction between the purified humus-like substance of compost and the purified Hbentonite-colloid, being passed over columns of first IRA-400 and then IR-120, was not observed from the additive effect on the titration curve. It was recognized from the titration curve that co-ordination compound of humus-like substance with aluminum was easily formed, but humus-like substance required more time to combine with iron than with aluminum. The formation of complex compound of humus-like substance with boric acid was not found from the cumulative effect on the titration curve. Accordingly, even if humuslike substance had adjacent hydroxyl groups, the positions of them were presumed not to be held in cis or ortho form, but in trans, meta, or para form. The conditions which were able to accelerate the decomposition of straw compost were observed as follows: (1) sufficient supply of air, (2) addition of moderate amount of calcium and nitrogen, and (3) maintenance of temperature adequate to thermophilic microorganisms. Compared true humic substance, rotted product, fulvic acid, and nonextractable organic matter from each two or three months elapsed compost, with those from one month elapsed one, respectively, in yields to the initial air dry straw material, the following relations were found: non-extractable organic matter decreased, and rotted product generally decreased or remained unchanged, also fulvic acid decreased, nevertheless true humic substance remained unchanged or increased. Thus, it may be assumed that rotted product was formed from decomposition of non-extractable organic matter, and the rotted product gradually converted to true humic substance according to progress of decomposition, and fulvic acid participated with the formation of true humic substance. True humic substance was not obtained from the compost prepared under perfect anaerobic condition, but only rotted product was extracted with mild extractants, even from three months elapsed one. On the contrary, from the compost under the most aerobic condition, even without nitrogen supplied, true humic substance was obtained in comparatively higher yield. In accordance with KONONOVA's opinion on soil humic acid, the formation of humuslike substance is supposed to be due to condensation of polyphenol produced by depoly-merization of lignin, carbohydrate and etc., with protein, polypeptide, and uronic acid which are decomposed products or metabolic substances by microorganisms. Thus, rotted product in humus-like substance is considered to be at the preliminary stage of condensation products by microorganisms, and true humic substance is presumed to be in the more advanced stage by aerobic microorganisms. This is emphasized by the fact that the formation of true humic substance appeared to participate with aerobic fermentation, and the chemical equivalent of true humic substance became less than that of rotted product.
- 大阪府立大学の論文
- 1964-03-31