Shao Ming-an

Effects of deep soil desiccation on artificial forestlands in different vegetation zones on the Loess Plateau of China

Abstract Deep soil desiccations are increasingly threatening artificial forests on the Loess Plateau of China. Soil moisture in 0–1000 cm soil layers of 23 kinds of tree and shrub forestlands was measured. Average soil moisture in 0–1000 cm soil profile of the forestlands was 10.84%, obviously lower than soil moisture in local natural grasslands and soil stable moisture. Average soil desic-cation intensity reached a medium level. Maximum soil water use depth was close to or over 1000 cm, and the thickness of desic-cated soil layers in forestlands reached or passed 800 cm.

Spatial Variability of Soil Particle Size Distribution and Fractal Features in Water-Wind Erosion Crisscross Region on the Loess Plateau of China

The spatial variability of soil particle size distribution and fractal dimension (D) values play important roles in both agriculture and environment. They impact soil texture, soil quality, and soil erosion. A grid sampling design was used to collect 325 topsoil (0-20 cm) samples from the Daye watershed (0.54 km2) in the water-wind erosion crisscross region of the Loess Plateau of China. Classical and geostatistical methods were combined to determine the spatial variability of soil particle size distribution and D values. The D values in the research area ranged from 1.37 to 2.66. There was a significant sigmoidal correlation between D values and the contents of clay, silt, and sand fractions. The D values of four different land uses could be arranged in the following order: woodland > farmland > grassland > shrubland. Values of D had moderate spatial autocorrelation, and clay, silt, and sand contents had strong spatial autocorrelation in the watershed landscape. The interpolation maps showed that D values could be an efficient way to evaluate the degree of soil desertification and degradation.

Landform affects on profile distribution of soil properties in black locust (Robinia pseudoacacia) land in loessial gully region of the Chinese Loess Plateau and its implications for vegetation restoration

Black locust (Robinia pseudoacacia) has been widely planted in the Chinese Loess Plateau and other parts of the world for soil and water conservation as a greening important forest species. The response of soil properties to black locust varies with landforms. This study was conducted to understand the effects of landforms on profile distribution of soil properties in black locust land in the loessial gully region of the Loess Plateau. Soil samples were collected in sloping land and gully bottom where black locust has planted for 21 years. For the collected soils, physicochemical, nutritional and enzymatic properties were determined. The results showed that 21 years’ growth of black locust increased organic matter and nitrogen stocks by 24.65 and 0.66 t hm-2, but decreased soil P stocks by 2.41 t hm-2 in 0 - 80 cm soil depth. Gully bottom soils were higher in organic matter, cation exchange capacity (CEC), total nitrogen and phosphorus, available potassium, alkaline phosphatase and invertase, while sloping land soils were higher in pH, nitrate, ammonium and Olsen P. Principle component analysis showed that the first principle component of soil properties can represent major variation of most properties and can reflect the effects of landform on distribution of soil properties in black locust land. These results indicate that the improvement of soil properties by black locust was more obvious in gully bottom than in sloping land and different management measures should be taken according to landforms, reflecting closed mutual interactions between soils and vegetation.

Fractal Dimension and Spatial Variability of Soil Water Infiltration Properties on Natural Slope in a Water-wind Erosion Interlaced Region

The research on soil water infiltration is of great significance to the acquisition of a better knowledge of hydrological circulation of the watershed. A water-wind erosion interlaced region is a place where the most serious soil and water loss happens on the Loess Plateau, and any study on soil infiltration properties and on their spatial variability of this region will do help to expose process of the soil erosion and improve precision of the watershed hydrological model. Of a natural slope (380 m long) in the Liudaogou catchment, which is typical of the water-wind erosion interlaced region, stable infiltration rate,mean infiltration rate and cumulate infiltration capacity within the initial 30 min were measured with a double-ring infiltrometer at 57 sampling sites, and the data were analyzed with both the traditional statistical method and the geostatistical method combined with the fractal theory. The results indicate: (1) the coefficient of variation (cv) of the above three parameters was respectively 0.48,0.36 and 0.40 and the spatial variability was medium in degree; (2)the fractal dimension of the three parameters was 1.88, 1.92 and 1.85, respectively, which shows that the difference was rather small between soil samples in values of the soil infiltration properties;and(3) the soil was not a medium with significant theoretical fractal phenomenon, and fractal features existed only in a specific range of space, and the range of spatial autocorrelation for stable infiltration rate,mean infiltration rate and cumulate infiltration capacity within the initial 30 min was 20~120 m, 20~140 m and 40~100 m, respectively.