Abstract: The aim of this study to clarify the effects of three land use types reclaimed from wetlands in Sanjiang Plain (upland, paddy field and artificial forest) on soil physicochemical properties and aggregate composition. The results showed that soil physicochemical properties significantly differed among different land use types. Compared with wetland, the three land use types significantly decreased soil water content and increased soil bulk density. Compared with wetland soil, soil available P in paddy field increased, while total N, total P, alkalihydrolyzable N and available P reduced in other land use types. There was a significantly higher reduction in upland and artificial forest than that in paddy field. The activities of soil urease, invertase and catalase under different land use types were significantly lower than those of wetland, with the reduction in paddy fields being significantly lower than that in upland and artificial forest. The activity of soil acid phosphatase in upland and artificial forest showed no significant different with wetland soil, whereas that in paddy field was lower. In addition, the concentrations of total organic C (TOC), microbial biomass C (MBC), dissolved organic C (DOC) and readily oxidized C (ROC) in soil under different land use types was lower than that in wetland soil. The decrease in TOC, MBC, DOC and ROC content was significantly higher in upland and artificial forest than that in paddy field. The soil aggregate composition with mechanical stability changed obviously under different land use types. The mean weight diameter (MWD) of soil in paddy field and upland was lower than that in wetland, with a significant decrease in uplands. However, soil MWD of artificial forest significantly increased compared to wetland. Our results indicated that the different land use types reclaimed from wetland significantly changed the soil physicochemical properties and aggregate composition. The damages of soil physicochemical properties, organic C stability and soil aggregate in paddy field were significantly lower than those in upland and artificial forest. Moreover, the destruction of soil physicochemical properties and structure in artificial forest was significantly lower than that in upland due to limited disturbance.

Key words: air temperature, precipitation, spring wheat, quality, insect pests., yield