| Two main parts were included in this paper. In the first part, the properties of organic matter were studied by analysing the status of organic-mineral complex, the combined status and composition of humus in steppe chernozem, steppe wind-blown soil and cropland wind-blown soil. In the second part, incubation experiments were conducted to deal mainly with the changes on amounts and E4/E6 ratios of humic acids (HA), fulvic acids (FA) during incubation time and the relations among the changes on them and incubation conditions (water, CO2, O2) in steppe chenozem. The objects are to provide scientific basis for clarifying the formation and transformation mechanism of soil humic substance (SHS), revealing the theoretical essence of Improving Soil Fertility by Organic Materials (ISFOM) and regulating soil fertility. Moreover, they are also give new data for research on soil organic matter and humic substances chemistry. The major results were as follows:1. Effects of different soil types and utilization patterns on the properties of soil organic matter The properties of soil organic matter were different in different soils and utilization patterns. Theamount of total organic carbon, biomass C, heavy fraction C, extractable humus (HE), loosely-combined status humus and humification degree were higher in chernozem than those in wind-blown soil. It indicated that the quality of humus from chernozem was better. Even the same soil type, the properties of organic matter were different in different plant cover. For example, the amounts of total organic carbon, biomass C, heavy fraction C, HE and different combined status humus were higher under steppe cover than under sunflower cover, but the humification degree was similar under both steppe and sunflower cover in wind-blown soil.2. Changes on amount and quality of organic carbon during incubation experimentsThe amounts of OC and water soluble substances (WSS) increased in soils after the addition of com stalk. They gradually decreased with prolonged incubation time, but still higher than CK at the end of incubation experiments (180th day). The amounts of OC were different under differentincubation conditions. At the end of incubation experiments, the amount of OC was lowest (21.05g/kg)under high water content and normal atmosphere, but was highest (23.74g/kg) under low water content, high CO, and low O2.During com stalk decomposition, HE-C, FA-C and Hu-C decreased; HA-C increased before 33th day, then decreased. But at the end of incubation experiments, HE-C, HA-C, FA-C and Hu-C of all treatments were still higher than that of CK. Among different treatments, HE-C, HA-C and Hu-C was highest under the low water and normal atmosphere; FA-C was highest under the low water, high CO2 and low O2; HE-C was lowest under the middle water, low CO2 and high O2; HA-C and Hu-C was lowest under high water and normal atmosphere; FA-C was lowest under middle water, low CO2 and high O2. The above results indicated that HE-C, HA-C, FA-C and Hu-C were different under different conditions of incubation.After the addition of com stalk, PQ of all treatments decreased rapidly. With prolonged incubation time, PQ gradually increased. But at the end of incubation experiments, PQ of all treatments were still lower than that of CK. PQ decreased with increasing water content under normal atmosphere, but it increased with increasing water content under high CO2 or high O2 at the 15* day. Whether water content was high or low, PQ was higher under low CO2 and high O2 than under high CO2 and low O2. It indicated that humincation degree was higher under high O2 or low CO2. It was also possible that humification degree was higher under high O2 and low CO2.After the addition of corn stalk, E4/E6 ratios of WSS increased in all treatments, which showed that molecular structure became simplified. E4/E6 ratios of WSS decreased with time, which showed that molecular structure became complexed. High water content was beneficial to the decrease of E/E6 ratios. E4/E6 ratios of HA firstly inc...
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