Spatial variability and distribution of soil nutrients in a catchment of the Loess Plateau in China

摘要

Inappropriate land use is one of the main reasons for soil erosion and nutrient loss in the hilly loess area of the Liudaogou catchment of the Loess Plateau, a typical topography area of hills and gullies. Good management practices, such as the nutrient variability for the different land uses (woodland, grassland, shrub land, farmland, and gully), would help the farmers. One study of the use of Geographic Information System (GIS) spatial analysis and geostatistic analysis was carried out in the catchment. The results showed that the trend of the content of clay and silt in the different soil ranks was: farmland < grassland < shrub land < gully soil. The sandy soil contained fewer nutrients than did the other soils. The farmland contains fewer total phosphorus (TP) and NH4+-N. The spatial dependence of the total nitrogen (TN) and the organic matter (OM) in the sandy soil is strong, but is only moderate in the other types of land use except for OM in farmland. The spatial dependence of TP in the different types of land use patterns is strong too, except in woodland, and the dependence of TP is moderate in grassland. The spatial dependence of NO3--N and NH4+-N is not strong, especially NO3--N in woodland, shrub land, and farmland. The dependence of NH4+-N is weak in grassland, gully, and farmland. In the catchment scale, the degree of spatial dependence (GD) is moderate for soil nutrients especially for TN and NH4+-N, but the different nutrients were modelled in different stationary models. The spatial variability of OM, TP, and NH4+-N was modelled by a Gaussian model, and the spatial variability of TN and NO3--N was modelled by an exponential equation. The nutrients' distribution in the catchment has been mapped by GIS. From the results, it was seen that annual grass played an important role in the conservation and improvement of soil quality in the Loess Plateau. In addition, the farmland should be given more fertilizer.