Organic matter changes in three parent soils with different long-termfertilizations in red soil regions of southern China

Soil organic matter changes in the 0-20 cm soil layer of Granite red soil, Quaternary red clay soil and Purple sandy shale soil were studied by using a long-term field experiment from 1982 to 2007 at Qiyang long-term raw soils anthropogenic mellowing field experiment site. There were 6 fertilizer treatments in the experiment. Results indicated that there are not any significant increases of soil organic matter contents in the no-fertilizer treatments, and there are slow increases of soil organic matter in the no-fertilization-straw returned treatments and annual increasing rates of the three soils are were 0.32, 0.20 and 0.17 g/kg, respectively. There are significant increases of soil organic matter contents in the chemical fertilization treatments, chemical fertilization-straw returned treatments, dry rice straw treatments and dry rice straw-straw returned treatments, especially in the chemical-straw returned treatment, and the annual increasing rates of the three soil are 0.48, 0.39 and 0.35 g/kg in the dry rice straw-straw returned treatments. In general, the increasing rate of Granite red soil is higher than that of Quaternary red clay soil and Purple sandy shale soil, respectively. This result suggests that the combined application of organic and chemical fertilizers, and straw returned is an effective measure of increasing soil organic matter.