Qingrui Chang

Identification of soil heavy metal sources and improvement in spatial mapping based on soil spectral information: A case study in northwest China

In a sewage irrigation area of northwest China, 52 topsoil samples were collected to measure the contents of arsenic (As), chromium (Cr), copper (Cu), mercury (Hg), manganese (Mn), nickel (Ni), lead (Pb) and zinc (Zn). To identify their sources, multivariate statistics and geostatistics were applied to separate pedogenic elements (As and Mn) from anthropogenic elements (Cr, Cu, Hg, Ni, Pb and Zn). The accumulation of soil Hg was mainly attributed to long-term sewage irrigation, whereas Cr, Ni and Zn were mainly from industrial activities and dust deposition. In addition to the impacts of industry and dust, traffic-related factors were the main sources of Pb and Cu contamination. Based on the relationships of heavy metals with various soil properties and reflectance spectra, co-kriging (CK) was used to improve the interpolation of heavy metals. Comparatively, soil spectra were more suitable as covariates due to their ease and low-cost of collecting as features.

Desert Soil Properties after Thirty Years of Vegetation Restoration in Northern Shaanxi Province of China

The vegetation restoration sequence of “grass-shrub-tree” has been successfully employed in many degraded areas; however, its applicability in desertified area reclamation is questionable. In this study, soil properties of a desertified land in the northern Shaanxi province of China were determined to assess the performance of this restoration sequence. Soil samples were collected from a contiguous area consisting of a control area of original desertified land (bare control) and three vegetation restoration sequence communities (continuous grass, grass-shrubs, and grass-shrub-trees) for 30 years. Results indicate that revegetation on the desertified area decreased soil bulk density (BD) and increased soil organic matter (SOM), cation exchange capacity (CEC), available nutrients (N, P, and K), and readily oxidizable carbon (ROC). Nonactive organic carbon (NAOC) and carbon pool management index (CMI) also improved in the top soil layer but not in the lower layer. Soil texture as well as total potassium (TK) and phosphorus (TP) did not change significantly. Comparing the three vegetation restoration communities, soil physical properties, SOM, and available nutrient content improved in grassland and shrubland, but declined in treeland, lability of C (L) was higher in the top layer of restored area than in bare control. L was 0.35–0.54 in grassland, 0.49–0.57 in shrubland, 0.43–0.52 in treeland, and 0.24 to 0.26 in bare control. Results of this study indicate that vegetation restoration on desertified land can improve soil properties. However, the popular restoration sequence of “grass-shrub-tree” is not appropriate for the restoration of semi-arid study area with low precipitation.

Impacts of landform, land use and soil type on soil chemical properties and enzymatic activities in a Loessial Gully watershed

Understanding the relationships among soil properties and, in turn, their relationships with landform, land use and soil type is essential for assessing soil quality and soil productivity. In this study, we examined the differences in the chemical properties and enzymatic activities of soils in a variety of landforms (plateau land, sloping land, terraced land and gully bottoms), land uses (woodland, grassland, cropland and orchard) and soil types (Chernozems, Cambisols and Regosols) in a gully watershed on the Loess Plateau, China. In total, 202 samples of surface soil (0–20 cm) were collected from different representative landscape units of the watershed. The chemical properties and enzymatic activities of the soils were measured. The results showed that chemical properties and enzymatic activities of the soils were all significantly influenced by landform, land use and soil type. There were interactive effects between landform and soil type. Soil pH varied the least, while invertase activity varied the most with landscape conditions. Soil pH, cation exchange capacity, organic carbon and total nitrogen contents, and enzymatic activities were all highest on plateau land and lowest on terraced land. Soil organic carbon and total nitrogen contents and alkaline phosphatase and invertase activities were higher in Chernozems than in Regosols, but the opposite trend was noted for pH, cation exchange capacity and catalase activity. Significantly higher values for most soil properties or enzymatic activities occurred in combinations including plateau land, Chernozems or Regosols. Soil pH was significantly lower in woodland soils than for other land uses, whereas the other properties had higher values in grassland and woodland soils than in orchard soils. The results from this study indicate the roles of landform, land use and soil type on the spatial patterns of chemical properties and enzymatic activities of soils and suggest that crops and orchards should be arranged on plateau land, and grasses and woodland on terraced and sloping land, respectively, for better economic and ecological efficiency in the area.

Fractal characteristics of soil under ecological restoration in the agro-pastoral transition zone of Northern China

Abstract Soil particle size distribution (PSD) is an important physical attribute due to its great influence on soil properties related to water movement, productivity, and soil erosion. In this study we use classical and geostatistical methods to identify the changes and characteristics of PSD and selected chemical properties in soil at the 0–20 cm layer from different vegetation covers of ecological restoration along the agro‐pastoral transition zone of northern China. The relationships between the fractal dimension of the PSD (Dm ) and selected soil properties are discussed. The results show that: (1) with the accumulation of vegetation cover, sand content dropped from 867 to 180 g kg‐1, and soil organic matter and nutrients increased significantly; (2) Dm ranged from 2.327 to 2.854. The higher the contents of clay, the higher the fractal dimension and the greater the vegetation; (3) significant linear regressions were found between Dm and soils properties such as sand, silt, clay, organic matter, total N, available N, P, K, cation exchange capacity and CaCO3. Therefore, the fractal model can be used as a m ain index to indicate the establishment of the restoration ecosystem and its degree of stabilisation.

Land use change impacts on the amount and quality of recharge water in the loess tablelands of China

Exploring how land use change (LUC) influences the amount and quality of recharge water is important for groundwater sustainability and land use planning. With loess of up to 200m in thickness and unsaturated zones up to 100m below the surface, the loess tablelands in China can store abundant groundwater resources. However, groundwater depletion and substantial LUC have been simultaneously observed. It is thus necessary to investigate the relationship between LUC and groundwater. We sampled 10-m soil profiles for three land use types (farmlands, apple orchards of 10 and 20years old). After measuring the chloride and nitrate concentration in soil pore water, the LUC effects on the amount and quality of recharge water quality were quantified based on the mass balance method. Results showed that soil moisture in aged (20-year-old) apple orchards was significantly reduced relative to that measured in farmlands and younger (10-year-old) orchards, where measured soil moistures were roughly equal. The accumulated nitrate‑nitrogen and the depth below which nitrate is stable was smallest in farmlands, intermediate in 10-year-old apple orchards, and largest under 20-year-old apple orchards. The diffuse recharge was 33.0±17.9mmyear-1, accounting for 7.3±1.8% of mean annual precipitation under farmlands; however, the conversion from farmlands to 20-year-old apple orchards reduced recharge by 42%. The nitrate infiltrating to groundwater annually was 4.9±2.9kghm-2 and 4.1±3.1kghm-2 under farmlands and 20-year-old apple orchards, respectively. The impacts of LUC over the past decades have not yet reached groundwater because of low recharge rates; further, the primary factor influencing groundwater quality is recharge rate rather than pollutant concentration. As such, the LUC from farmland to apple orchard has little impact on short-term groundwater recharge and quality; long term impact, however, may be significant.

Effects of Long-Term Fertilization on Soil Organic Carbon and Nitrogen in a Highland Agroecosystem

Abstract The effects of fertilization on the distributions of organic carbon (OC) and nitrogen (N) in soil aggregates and whether these effects vary with cropping system have not been well addressed. Such information is important for understanding the sequestration of OC and N in agricultural soils. In this study, the distributions of OC and N associated with soil aggregates were analyzed in different fertilization treatments in a continuous winter wheat cropping system and a legume-grain rotation system in a 27-year field experiment, to understand the effects of long-term fertilization on the distributions of OC and N in aggregates and to examine the recovery of soil OC and N in a highland agroecosystem. Manure fertilizer significantly decreased soil bulk density but increased the amount of coarse fractions and their associated OC and N stocks in the soils of both systems. Fertilizers N + phosphorus (P) and manure had similar effects on total soil OC and N stocks in both systems, but had larger effects on the OC and N stocks in > 2 mm aggregates in the legume-grain rotation system than in the continuous winter wheat system. The application of P increased the OC and N stocks in > 2 mm aggregates and decreased the loss of N from chemical fertilizers in the legume-grain rotation system. The results from this study suggested that P fertilizer should be applied for legume-included cropping systems and that manure with or without chemical fertilizers should be applied for semiarid cropping systems in order to enhance OC and N accumulation in soils.