黄土高原小流域土壤水分及全氮的垂直变异

为了研究黄土高原土壤中水分及全氮垂直分布及变异情况，对陕北神木县六道沟小流域中苜蓿地、荒草地、农地、柠条地以及油松地5种不同植被类型下0～800 cm土层中土壤含水率和土壤全氮进行了测定和分析。土壤含水率在垂直方向上呈现出干湿交替的层状分布。植被类型影响土壤水分含量的垂直剖面分布；各植被类型下相对高湿层和低湿层出现的深度不同；不同深度土层平均土壤含水率不同。农地及退耕荒草地土壤水分涵养较好，垂直方向上含水率变化较大；人工植被苜蓿、柠条消耗土壤水分较多，土壤含水率变化相对平缓；油松地平均土壤含水率及变化幅度居中。研究区域中，土壤全氮含量水平较低，表层发生陡降后，在20 cm以下土层中仍以很小的变幅降低，变化平缓。柠条地土壤全氮含量高于其他植被类型。

Vertical variations of soil moisture and total nitrogen in small catchment on Loess Plateau

This study was to investigate the vertical distribution and variations of soil moisture and soil total nitrogen under different vegetation types on the Loess Plateau. Soil moisture and soil total nitrogen in 0-800 cm profile under five vegetation types, i.e., alfalfa, wild grass, crop, caragana and pine, were measured and analyzed. Soil moisture had a remarkable stratified distribution in the vertical direction, with vicissitudinary dry and wet layers. The vertical distribution of soil moisture was affected by vegetation type. Different vegetation type had different occurrence depth of relatively dry and wet layers and different average soil moisture. Cropland and grassland performed better in soil water retention. Soil moisture of these two vegetation types showed greater vertical variation. The two planted vegetation types, alfalfa and caragana, consumed much more soil water, and thus did not have a pronounced vertical variation in soil moisture. Soil moisture under pine trees had middle value and moderate variation extent. Soil total nitrogen of the study area was low, with a sudden decline in top 20 cm layer and still gently decreased below 20 cm depth. Soil total nitrogen was higher under caragana than those under other four vegetation types.