| Fire is a special factor in ecosystem and occurs on forest and grassland sometimes. Many researches on this have been made by researchers at home and abroad to discuss the effects of fire on forest and grassland fire. But none was made about soil from cultivated land where people used to burning the straws after harvest in some regions of china. In this article, by discussing the changes of quantity and quality of soil organic matter after laboratory heating and harvest burning. we want to reveal the effects of burning on the components of soil organic matter with straws. And the main results are as follow:(1) The changes of soil organic matter components varied from the intensity of laboratory heating. In the temperature range from100℃to360℃, the contents of dissolved organic carbon increased initially and then fell down following the temperature rising, meanwhile, the neutral sugars and uronic acid possessed the same trend as that. A significant increasing of dissolved organic carbon was observed at the moderate intensity (200℃) by3-7times of the unheated value. Consequently, when heated over300℃, the dissolved organic carbon, neutral sugars and uronic acid, especially the neutral sugars decreased obviously which indicated raising the temperature of soil properly can make the content of dissolved organic matter increasing. After heating, the humic acid increased slightly earlier and then decreased as the temperature rising, but fulvic acid showed less thermal resistance to high intensity and decreased at300℃. As a result, the HA/FA ratio increased greatly which meaned the humus at this temperature was most polymerized than others. Meanwhile, the FTIR emission spectroscopy of humic acid record aliphatic material of humic acid decreased while aromatic structures increased at this temperature. That indicated the residues which may be consist of pyrolysis or neoformed humic acid and something else possessed higher resistance to thermal, and can make the humification degree increasing. Moreover, the intensity of C=C stretching vibration of humic acid and-CH3、-CH2groups in fulvic acid reduced and enhanced respectively suggested that the aliphatic fractions and the aromatic structures increased and decreased respectively at. That was corresponding to the significantly increase of soil dissolved organic matter and the increase of E4/E6of humic acid at this intensity which indicated the soil possessed higher condensation of the aromatic structure and(2) Soil organic matter changed obviously with the increasing burning frequency. After burning, only the upper organic matter in decreased noticeable which meaned the fast but intense burning do not transfer much heat down to more than few centimeters below the surface. Dissolved organic matter was the active compound in the soil which had visible mobility. The oxidation decomposition of adventive and original organic matter in soil became rapidly when the burning start which result in the increase of dissolved organic matter, the content of DOM in the30th post-burning soil has been2-3times of the untreated one. Moreover, the neutral sugars and uronic acid possessed the same trends as dissolved organic matter. Different soils had various response to thermal, so the humic substances in three studied soils didn’t perform the same trends as frequency altered, but both the content of humic acid and the ratio of HA/FA and E4/E6increased or decreased regularity as burning increasing, and the alteration of fulvic acid effected the changes of HA/FA ratio dominantly. In addition, the aromatic fractions and C-OH、C-O structures increased as times increasing, but the transform of HA were not noticeable due to the strong thermal resistance and condensation of the aromatic structure. |
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