荒漠地区土壤初始状况对水平入渗的影响

THE INFLUENCE OF INITIAL SOIL CONDITIONS ON WATER PENETRATION AND SOIL MOISTURE DISTRIBUTION

通过对沙坡头荒漠地区人工植被固沙区生物土壤结皮与固沙区外天然沙丘沙以及天然植被红砂、珍珠分布区砂粘土在不同初始含水率(θi)条件下土壤水平入渗过程的对比试验研究,探讨土壤质地以及θi对水平入渗系数(λf)、剖面平均含水率(θm)状况的影响。生物土壤结皮对降水入渗量的截持作用大于沙丘沙,因而将显著地改变降水入渗过程中土壤水分的再分配格局,减少降水对深层土壤(沙丘沙)的有效补给。通过对土壤剖面平均含水率θm与距离湿润锋前缘0～5cm、5～10cm处体积含水率θfA、θfB比较,生物土壤结皮的θm、θfA和θfB分别约为沙丘沙的1.5倍。

More than forty years of revegetation using mainly Artemisia ordosica, and Caragana korshinskii at Shapotou Desert Experimental Research Station near Lanzhou has established a dwarfshrub and herbaceous cover on stabilized sand dunes. Situated in southeast Tengger desert at 1 330 m elevation, it has an average annual rainfall of 191 mm with 83% received from May to September. Precipitation, as the sole source of water replenishment in the semiarid area, plays a pertinent role in sustaining the desert ecosystem. The water penetration experiment on soils of microbiotic crust, fine sandy loam and pure dune sand at different initial soil moisture content (θi) were conducted by the horizontal penetration equipment in the laboratory. The soil moisture distribution was tested by sampling core soil at an interval of 5 cm from the point of water entrance. The results indicated that, for the selected experimental soils, water penetration coefficient (λf) were decreased in response to an increased θi, respectively. The λf of sand was much more high as compared to that of microbiotic soil crust and sandy loam at every single θi. The sandy loam has a less sharp decline feature of λf with an increased θi, in comparing with that of microbiotic soil crust and dune sand. Due to the soil texture peculiarity, λf is 4 times in microbiotic soil crust than that in dune sand, in spite of initial soil moisture content. The microbiotic soil crust has a value of 1.5 times of average soil moisture content both along the soil profile and at a distance of 0～5 cm and 5～10 cm from the wetting front than that of dune sand. We may conclude that the microbiotic soil crust has a more hydrophilic property, which contributes a big majority proportion in retaining rainfall than dune sand does in Shapotou regions.