以小流域为单元,分析了黄土高原沟壑区化肥投入、土壤NO₃^--N积累及其影响因素。结果表明,化肥投入是流域土地利用结构调整的重要支撑和保证因素,而流域土地利用结构的变化进一步拉动了化肥的投入。目前施肥条件下,流域内坡地果园存在显著的NO₃^--N积累,其积累量高于农田土壤,应作为今后重点监测对象。农田系统中,小麦或玉米连作土壤中NO₃^--N的积累最显著,通过作物之间的轮作可显著降低剖面中NO₃^--N的深层积累。土壤NO₃^--N的积累是小流域治理过程中产生的问题,与流域氮肥投入、氮肥吸收利用和土壤水分演变密切相关。

Chemical fertilizer input was the key factor affecting soil ecological environment and land productivity in a small watershed.Wangdonggou watershed is just the type of gully region on the Loess Plateau.The monitoring of chemical fertilizer input,land use change and land pro-ductivity started in the small watershed in1984.NO₃^--N accumulation in soil profiles of0～300cm was determined in croplands with continuous and rotation cropping systems,apple yard with7-and15-years of apple trees as well as fallow land in the small watershed.Fertilizer input,NO₃^--N accumulation,and land use structure were analyzed in the small watershed.The results showed that chemical fertilizer led to significant increase in land productivity and decrease in the area of cropland.Chemical fertilizer input was an important driver to land use structure change,the area of apple yard land increased significantly from1984to1995.Changes in land use structure further affected input of chemical fertilizer into the small watershed.NO₃^--N accu-mulation in soil depth of100～200cm has been significantly produced in cropland and apple yard land under current conventional fertilization practices.NO₃^--N accumulation in apple yard land was greater than that in cropland.NO₃^--N accumulation in continuous cropping systems was greater than that in rotational cropping systems.NO₃^--N accumulation was obviously related to fertilizer input,fertilizer uptake by crops,and soil moisture change in the small watershed.