民勤绿洲区撂荒农耕地抗风蚀效果

通过风洞试验,在5个风速下对民勤绿洲区5种不同撂荒年限农耕地的土壤风蚀速率、0—20cm风沙流结构进行了模拟观测研究。结果表明:农耕地撂荒20年后土壤风蚀速率明显增加,撂荒30,40年土壤风蚀速率是其他处理的2.40～4.97倍。不同撂荒年限土壤风蚀速率均随风速的增大呈指数函数递增,但在撂荒30,40年条件下递增较快。风速为14m/s是民勤绿洲农田土壤风蚀加剧的转折点,当风速>14m/s时,农耕地撂荒20年后的土壤风蚀速率明显高于撂荒20年内。0—20cm内,农耕地撂荒20年内和撂荒20年后输沙率与高度分别呈负线性和负指数关系,农耕地撂荒20年内0—4cm输沙量和输沙量百分比(Q0—4/Q0—20)均低于撂荒30,40年。随着撂荒年限的延长,农田表层不可蚀性颗粒(粒径≥1mm的团聚体及粗砂砾)的含量明显降低,且土壤风蚀速率随不可蚀性颗粒含量的增加呈非线性降低趋势。因此,增强民勤荒漠绿洲区撂荒农耕地抗风蚀能力需适当减少撂荒年限。

Effect of Wind Erosion Resistance of the Abandoned Cropland in Minqin Desert-oasis Region

Through wind tunnel experiment in the Minqin oasis desert region, the soil wind erosion rate and blown sand structure of 0-20 cm in five cropland abandoned for different years were simulated under five wind speeds. The results indicated that mean soil wind erosion rate increased significantly in the cropland abandoned more than 20 years, and the soil wind erosion rates of abandoned 30 and 40 years croplands was 2.40~4.97 times that of other treatments. The exponential functions were found between rate of wind erosion and wind speed in all the five abandoned cropland, and the wind erosion rate increased faster with the increasing of wind speed in 30 and 40 years abandoned cropland. Wind speed of 14 m/s was the significant point for aggravating soil wind erosion. When the wind speed was greater than 14 m/s, soil wind erosion rate of cropland abandoned more than 20 years was significantly higher than that of abandoned within 20 years. In 0-20 cm, there was a negative linear relationship between the rate of sediment transport and the height in the cropland abandoned within 20 years, and negative exponential functions were founded in cropland abandoned 30 or 40 years. The total volume of sand transport in 0-4 cm and sand transport percent between 0-4 cm and 0-20 cm (Q_0-4/Q_0-20) in the cropland abandoned within 20 years were less than those of cropland abandoned more than 20 years. With the increasing of the abandoned years, the content of nonerodible soil particles (aggregates and coarse grits larger than 1mm) in the surface soil layer significantly reduced, and soil wind erosion rate decreased by a negative line function with the increasing of nonerodible soil particles content. Thus abandoned years should be properly reduced in order to increase soil resistance to wind erosion in this region.