半干旱区农田灌丛沙堆形态及沉积特征

采用野外观测和采样分析的方法对半干旱区农田灌丛沙堆形态及沉积特征进行了研究，结果表明:研究区农田灌丛沙堆水平尺度为4.4 m，长宽比为1.5，体积庞大且较为细长，走向与农田垄向相同。农田灌丛沙堆的湿度及硬度随部位的不同而发生变化，沙堆东侧湿度最大，为10.19%，硬度最小，为4.12 kg/cm²；南侧湿度最小，为1.03%，硬度最大，为15.9 kg/cm²；坡顶湿度较小，硬度较大，沙堆坡底硬度较大。沙堆整体的平均粒径、分选性低于周边农田，从迎风坡坡脚→迎风坡坡中→坡顶→背风坡坡中，平均粒径、分选性逐渐降低。垂直剖面颗粒粒径随着深度的加大有逐渐增大的趋势，分选性变差。除植被盖度、风力强度和沙源3个主要因素外，人为耕作也是一个影响农田灌丛沙堆形成演化的重要因素。

Morphology and Sedimentary Characteristics of Nebkhas in Semi-Arid Farmland

The morphology and sedimentary characteristics of the Nebkhas in semi-arid farmland was studies by means of field observation and sampling. The results show that the Nebkhas in the area is huge and long and stretches along the ridges, with the horizontal scale of 4.4 m and the length-width ratio of 1.5. The moisture and the hardness of the Nebkhas vary in different parts of the farmland. The moisture in the east of the Nebkhas is the greatest, being 10.19% and the hardness is the smallest, being 4.12 kg/cm²; the moisture in the south is the smallest, being 1.03% and the hardness is the greatest, being 15.9 kg/cm². The top of the Nebkhas is moister and harder and the bottom is harder, too. The average particle size and the sorting of the Nebkhas are lower than those of the surrounding farmland, which gradually decrease in the sequence of windward slope foot- in the windward slope-the top- in the leeward slope. The particle sizes of vertical profile gradually increase with the depth and the sorting reduces. In addition to the three main factors of vegetation cover, wind strength, and sand, farming is an important factor which influences the formation and evolution of farmland nebkhas.