中文摘要：

本文通过棕壤长期定位施肥试验,研究了玉米-玉米-大豆轮作条件下不同施肥处理土壤有机碳及其不同密度组分的变化及其影响因素。结果表明：经过27年的长期不同施肥,土壤有机碳含量有了明显变化,总的变化趋势是：高量有机肥区（12.30gkg^-1）〉低量有机肥区（11.41gkg^-1）〉化肥区（9.95gkg^-1）〉1979年（试验前9.03gkg^-1）〉对照处理（8.23gkg^-1）,尤其以高量有机肥配施化肥处理的有机碳水平最高,氮磷钾配合施用有机碳水平要高于其它单施化肥处理;长期施肥可以显著提高土壤中轻组部分含量和轻组有机碳含量,不同施肥处理间差异显著。单施化肥处理,特别是氮磷钾配合施用,轻组部分数量和轻组有机碳含量高于无肥处理和试验前土壤。有机无机肥配合施用轻组有机碳含量明显高于单施化肥处理。施用不同肥料均可以提高土壤重组有机碳含量,有机无机肥配施效果明显。

英文摘要：

Long-term fertilization treatment, organic manure applying amount and maize-maize-soybean rotation were summarized as follows. For long-term different fertilization treatments with different rotates of 27 years, the total soil organic carbon contents changed obviously, the total changes of soil organic carbon were ： higher organic manure treatment （12.03gkg^-1）〉 lower organic manure treatment （11.41gkg^-1）〉 chemical fertilizer treatment （9.95gkg^-1）〉1979 year（before examination 9.03gkg^-1）〉no fertilizer treatment（8.23gkg^-1）. Especically, the treatment of applying the higher level organic manure and inorganic fertilizer had the highest organic carbon level. The soil organic carbon concentration of applying nitrogen, phosphorous and potassium fertilizer was higher than that of other single inorganic fertilizer treatment. Long-term fertilization could increase the LFOC and light fraction content distinctly, the different treatments differed significantly. Applying single fertilizer, especially applying N, P and K, the LFOC and light fraction content were higher than CK and soil before trial. The LFOC of applying inorganic fertilizer and organic manure were higher than that of single inorganic carbon. It is true that all the treatments applying different fertilizers could increase HFOC, applying inorganic fertilizer and organic manure＇s effect significantly. About all, sequence using organic manure could increase content of soil organic carbon, so increase content of humus in soil, accelerate release of efficiency nutrients in soil and absorption-stimulating action of crop.