土壤腐殖质的形成和稳定性研究

Humic composition, the relative proportion of humic acid (HA) to fulvic acid (FA), is the most important feature of soil organic matter (SOM). It affects not only soil fertility, but also soil environment and quality. But so far, it is not well known that the formed sequence of HA and FA, the renewed rate and dynamic changes in amounts and properties of the old SOM, and the relationship between the above changes and environmental factors during plant remains or materials decomposition. In our study, an incubation experiment was arranged by adding C4 plant materials to a dark-brown soil, a paddy soil and their corresponding ignited soil, and 14C-libled organic materials to a sandy loam soil. The formation of HA, FA and their dynamic changes in amounts and properties; the distribution of the new formed SOM in soil microorganism biomass (SBM), in water soluble substances (WSS), in different chemical fractions such as loosely-combined humus(HEI), stable-combined humus(HEII) and humin(HN) and in different physical fractions such as free light fraction(FLF), occluded light fraction(OLF) and heavy fraction(HF); the effects of environmental factors on formation and transformation of HA and FA were studied by the methods of δ13C, 14C, modified humus composition method and sodium polytanstate (SPT). The method for researching thermodynamical stability of SOM was primarily discussed. The aims of this research are to clarify the formation and transformation mechanism of HA, FA and to provide new data for the mechanism of improving soil fertility by organic material (ISFOM). The main results were as follows:. 1) δ13C values of soils and its fractions. For different soils, δ13C values of paddy soil and dark-brown soil (bean-wheat rotation) were lower, near to -25‰; but those of brown soil, dark soil and meadow soil in which planted C4 corps were higher, about -20‰. δ13C values of FA was generally higher than that of HA or total SOM in the same soil. It might be related that FA contained more 13C-rich carbohydrate. δ13C values of HEI-HA was higher than that of HEII-HA, which indicated that the former was close to FA. δ13C value of humin which contained more lipid was unexpected higher than that of total SOM. δ13C value of small molecular HA (molecular weight<2000) obvious increase, indicated small molecular HA contained more 13C-rich compound.. 2) The dynamic changes inδ13C values of soils, HA, and FA after corn stalk addition . Whether dark-brown soil or paddy soil, their δ13C values obviously increased after the addition of corn stalk. With prolonged time, the increase extent of δ13C values decreased, and it become to declined or appeared a decline tendency in a certain time. But at the end of incubation, δ13C values of incubated soils were still higher than that of original soil (CK). The changes of δ13C values could reflect the changes in amount of soil organic carbon (SOC), but they mainly reflected the changes in amount of light fraction (LF) or new formed SOC (e.g. C4-C). With prolonged time, the amounts of C4-C and C3-C all decreased, but the decrease rate of the latter was relative lower. The residual percentage of corn stalk and original SOM were 30% and 90% respectively at 360th day.. It was the same that the changes in amount of C4-C and C3-C in HA and FA as in soils. Whether new formed humic substances or old ones, with the prologed incubation time, the amount of HA increased first and then decreased, the turning point was at 15th day; but that of FA presented a declining tendency. It was founded that a remarkable correlation between C4t (the amounts of C4-C at t time) andδ13C values of HA, FA; but not remarkable correlation between C3t (the amounts of C3-C at t time) andδ13C values of HA, FA.. 3) Dynamic changes in the ratios of HA/FA or after the corn stalk addition. Whether dark-brown soil or paddy soil, the forming rate of FA was faster than that of HA in the initial stage of incubation; with the prolonged time, FA transformed into HA or they transformed each other. In the or

应用σ13Ｃ新方法，研究特定培养条件下胡敏酸、富里酸形成的时间顺序和更新速度及其在进一步的腐化过程中各自数量和发生特性的动态变化规律。应用元素组成和土壤条件参数新方法，计算不同土壤腐殖质组分的吉普斯生成自由能和热力学稳定性范围。以阐明土壤腐殖质的形成和转化规律，并解释和推测腐殖质组成的空间变异和分布规律。..