Processes and Mechanisms of Soil Desertification in Semiarid Areas,Northern China

Land desertification is one of the most main types of land degradation in the arid and semiarid region,northern China.However,there is a lack of knowledge on mechanisms of soil degradation in desertification processes in this region.A field experiment was conducted from 2002 to 2003 on desertified land with gradients of wind erosion to investigate changes in soil properties resulting from desertification in the Horqin sandy land.The results showed that physical and chemical properties exhibited greater differences among different particles-size fractions.Soil fine particles had lower soil bulk density and higher soil hardness,capillary water-holding and nutrient contents.Soil bulk density increased by 10.32%,and soil hardness,capillary water-holding,organic C,total N decreased by 99.15%,51.23%,83.73% and 80.24% from clay+silt fraction to coarse sand fraction,respectively.In land desertification processes,the soil physical and chemical properties changed significantly with desertification.Compared to undesertified land,coarse sand contents non-capillary porosity and bulk density increased by 35.04%,117.50% and 21.7%,fine sand,clay+silt,total porosity,capillary porosity,field water-holding,capillary water-holding,soil organic C,total N and P,available N and P decreased by 77.78%,70.00%,15.38%,27.49%,54.34%,37.54%,64.15%,70.77%,65.90%,66.32% and 50.59%,respectively in the severely desertified land.The results of correlation analysis showed that soil organic C,total N and P,soil moisture and hardness had a significant positive correlation with the soil clay and silt contents,and had a significant negative correlation with coarse sand content.Those results showed that selective removal of the finest soil particles that contain rich nutrients and higher water-holding capacity and hardness under wind erosion was the primary mechanism of soil degradation in land desertification processes.