我国北方半干旱地区土壤的沙漠化演变过程与机制

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

土地沙漠化是我国北方干旱半干旱地区土地退化最严重的类型之一。但迄今为止,人们对这一地区土地沙漠化过程中土壤沙化过程和机制的了解还不够透彻。2002-2003年,我们在科尔沁沙地选择具有明显沙漠化梯度的一个区域,调查和研究了土壤沙漠化演变过程和机制。结果表明,在科尔沁沙地,不同粒径土壤颗粒的理化特性具有较大差异,其中土壤粘粉粒和粗沙相比,具有较低的土壤容重和较高的土壤结持力、起沙风速、毛管持水力和养分含量。从土壤粘粉粒到粗沙,容重增加了10.32%,结持力、毛管持水量、有机碳、全氮分别下降了99.15%,51.23%,83.73%和80.24%。沙漠化过程中,土壤的理化性质随着土地沙漠化程度的增强而明显恶化。和非沙漠化土地相比,严重沙漠化土地的土壤粗沙含量、非毛管孔隙度和容重分别增加了35.04%,117.50%和21.7%,细沙含量、粘粉粒含量、总孔隙度、毛管孔隙度、田间持水量、毛管持水量、土壤有机碳、全氮、全磷、有效氮和有效磷分别下降了77.78%,70.00%,15.38%,27.49%,54.34%,37.54%,64.15%,70.77%,65.90%,66.32%和50.59%。相关分析结果表明,沙漠化过程中,土壤有机碳、全氮、全磷、土壤含水量和土壤结持力的变化与土壤粘粉粒的减少呈明显正相关,与土壤粗沙含量的增加呈明显负相关。这说明,沙漠化过程中,由于风蚀而导致的富含养分和具有较高持水能力的土壤细颗粒的损失,是沙漠化过程中土壤退化的主要机制。

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 hulk 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-k-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 in- creased by 35.04%, 117.50% and 21.7%, fine sand, clay＋silt, total porosity, capillary porosity, field waterholding, 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.