The effects of soil sand contents on characteristics of humic acids along soil profiles

It is generally accepted that the compositions and properties of soil organic matter（SOM） are in?uenced by many factors. In order to reveal the effects of soil texture on characteristics and dynamics of SOM and its sub-fraction,humic acid（HA）, along two soil pro?les, a yellow soil pro?le and a purplish soil pro?le, under the same climate and vegetation conditions were determined. Results indicate that the decomposition and humi?cation degrees of SOM and HA of the purplish soils are higher than those of the corresponding yellow soils indicated by A/O–A ratios of HAs, TOCs and HA yields of bulk soil samples, nevertheless, the development degree of the purplish soil is lower than that of the yellow soil. The variations of E4/E6 ratios of HAs along the soil pro?les indicate the overall molecular sizes of HAs decreased downward along the soil pro?les.A/O–A ratios of HAs decreased downward along both the soil pro?les indicate that humi?cation processes decrease downward along both the soil pro?les. Leaching of SOM shows signi?cant effects on the distribution and characteristics of HAs in the yellow soil pro?le but the purplish soil pro?le, which is consistent with the higher hydrophobicity of HAs in purplish soils, shows that the distribution characteristics of SOM along the soil pro?les are a complex result of the combination of soil texture and characteristics of SOM itself. The remarkably different sand contents are concluded tentatively as one of reasons to the different distributions and dynamics of HAs along the soil pro?les,however, to profoundly understand the evolution and transport of SOM along soil pro?les needs more researches.