Liang Xinqiang

Effect of composting process on phytotoxicity and speciation of copper, zinc and lead in sewage sludge and swine manure.

The concentration and bioavailability of heavy metals in composted organic wastes have negative environmental impacts following land application. Aerobic composting procedures were conducted to investigate the influences of selected parameters on heavy metal speciation and phytotoxicity. Results showed that both of sewage sludge (SSC) and swine manure (SMC) composting systems decreased the pH, the content of organic matter (OM) and dissolved organic carbon (DOC), and total amounts of Cu, Zn and Pb. Sequential extraction showed that readily extractible fractions of exchangeable and carbonate in Cu and Zn increased during SSC composting but decreased during SMC composting, thus their bioavailability factors (BF) enhanced in SSC but declined in SMC. The fraction of reducible iron and manganese (FeMnOX) of Cu and Zn in SSC and FeMnOX-Cu in SMC decreased, but FeMnOX-Zn in SMC gradually increased in the process of compost. In contrast, the changes of Pb distributions were similar in two organic wastes. Pb was preferentially bound to the residual fraction and its BF decreased. The evolution of heavy metal distributions and BF depended on not only total metal concentrations but also the other properties, such as pH, decomposition of OM and decline of DOC. The germination rate (RSG), root growth (RRG) and germination index (GI) of pakchoi (Brassica Chinensis L.) increased during the composting process. Linear regression analysis demonstrated that GI, which could represent phytotoxic behavior to the plants, could be poorly predicted by BF or total amount of metals, i.e., BF-Zn, T-Cu. However, the inclusion of other physicochemical parameters (pH, OM and DOC) could enhance the linear regression significances (R).

A simple approach to assess N load capacity of rice paddy fields in the southern Taihu Lake watershed

High nitrogen (N) leaching from irrigated agricultural soils is the result of N input exceeding soil N load capacity (NLC). A simple approach was developed in this research to assess the NLC of paddy soils in the southern Taihu Lake watershed. Paddy soils were classified into four types (Submergenic, Illuvium, Gleyed, and Percogenic) and 28 soil samples representing all four types were collected from across the region. The NLC values of the paddy soils were assessed using a split-line model and the spatial variability of the NLC among various rice paddy soils in the region was also evaluated with Kriging analysis. Results showed the NLC of paddy soils were both soil type and background N content related. The critical N sorption values (NLC plus soil N background) of the Gleyed, Illuvium, Submergenic, and Percogenic paddy soil samples varied from 283.1 to 315.6 mg kg(-1), 203.0 to 270.2 mg kg(-1), 240.6 to 254.4 mg kg(-1), and 177.4 to 186.2 mg kg(-1), respectively. However, on average the NLC of paddy soils in the region was 80.3 mg kg(-1), and the corresponding environmental N load threshold was around 110 kg N ha(-1). Geo-statistic results showed that the NLCs were unevenly distributed throughout the rice paddy dominated areas of the southern Taihu Lake watershed. The NLC assessment approach and spatial distribution information provided helpful guidance to set an environmental N threshold for best N management and hence reduce degradation of water for the whole rice ecosystem.