| The mudflats along the East Coast of China can be important alternative sources for arable lands if amended by large amount of organic fertilizers. Rich in organic matter and other nutrients, sewage sludge has been considered as the economic choice for "initial fertility driving agent". Infertile mudflat soil could obtain the initial fertility through one-time sewage sludge amendment to support growth of green manure. Ryegrass after returning can be decomposed, and converted into soil organic matter. By the cycles of planting and returning green manures, organic matter in mudflat soils would rapidly increase through self-accumulation. Therefore, the objective of the present work was to investigate the impact of sewage sludge amendment (SSA) as an initial fertility driver at 0,30,75,150, and 300 t ha-1 rates on soil physicochemical properties, green manure growth, biomass and heavy metal accumulation in mudflat soil. The results showed as follows:(1) The sewage sludge as an initial fertility driver improved significantly physicochemical properties of mudflat soil. The decrement in salinity and pH were 37.9%,59.8%,66.6%,73.1% and 5.3%,9.0%,14.7%,18.8% at 30,75,150 and 300t ha-1 SSA rates, respectively, as compared to the unamended soil. The SSA increased porosity, CEC, contents of organic matter, N and P in mudflat soil. The increment in organic matter was 97.5%,167.9%,320.2% and 352.9% at 30,75, 150 and 300t ha-1 SSA rates, respectively, as compared to the unamended soil. The increment in >0.25 mm soil aggregates in 0-10 and 10-20 cm soil layers were 16.3%,25.5%,26.7%,31.7% and 12.1%,14.8%,18.1%,32.5%.(2) The sewage sludge as an initial fertility driver increased content of total Cd, Cu, Pb and Zn in mudflat soil. The SSA increased total Cd, Cu and Zn concentrations at 75,150 and 300 t ha"1 rates (p<0.05), and total Pb concentrations at 150 and 300t ha-1 rates (p<0.05). The available metal concentrations increased with the SSA. There were sharp increases in soil available Cd, Cu, Ni and Zn with increasing SSA rates, whereas the available Mn and Pb showed only minor increases with increasing SSA rates.(3) The sewage sludge as an initial fertility driver increased biomass of green manures. The increment in average biomass of five green manures was 81.1%,130.3%,179.7%and 222.3% at 30,75,150 and 300 t ha-1 SSA rates, respectively, as compared to the unamended soil. The increment in accumulation of N and P were 184.4%,259.0%,413.0%,683.0%and 296.8%, 341.0%,624.8%,951.2%at 30,75,150 and 300 t ha"1 SSA rates, respectively, as compared to the unamended soil. Heavy metal concentrations in grain of maize were still lower than the safety standard for food in China. |
