Abstract:

To understand the spatial variation characteristics of fertility quality of the purple soils and provide basis for scientific utilization and improvement of the soils in Hangzhou administrative region, eight representative hilly slopes covered with the purple soils were selected in the western mountainous area of the region. The surface soil samples were collected according to the terrain positions (slope bottom, slope foot, middle slope, upper slope and slope top) and utilization modes (forest land and upland), and the fertility indexes of the soils were analyzed. The results showed that the effective soil thickness increased gradually from the top of the slope to the slope foot and the bottom of the slope. The genetic horizon combination of soil profiles changed from A-C or A-R to A-B-C, and the morphologic structure of the surface soils changed from single particles to block structure. Soil gravel and sand contents, pH value and total calcium gradually decreased, while soil clay, organic carbon, total potassium, total phosphorus, available nutrients and CEC gradually increased. The organic carbon in the purple soils was mainly mineral-bound, followed by particular organic carbon, and the content of free organic carbon in the soils was less. From the top of the slope to the slope foot and the bottom of the slope, the proportions of both free organic carbon and mineral combined organic carbon in total organic carbon gradually increased, while that of particular organic carbon in total organic carbon decreased gradually. The soil moisture content in different terrain positions increased gradually from the top of the slope through the upper slope, the middle slope to the slope foot and the bottom of the slope, but difference of the soil moisture content among slope positions was greater in dry season than in rainy season. After the forest land was reclaimed to upland, the contents of soil acidity, total phosphorus, available phosphorus and the proportion of mineral bound organic carbon to total organic carbon increased significantly, but that of particular organic carbon to total organic carbon and moisture content of the soils decreased. Compared with forest land, the upland soils at the top, upper slope and middle slope had lower gravel and sand contents, meanwhile the upland soils at the slope foot and bottom had higher gravel and sand contents. The soil clay content and water holding capacity of upland were all lower than those of forestland. The results showed that the differences of soil properties of different slope positions should be considered in the development and utilization of purple soils.

Key words: purple soil, organic carbon components, physical and chemical properties, topography, utilization pattern, spatial variation