Collection of soil samples and sample handling
Soil samples were collected after harvest of the late rice in 2009. Prior to sampling, the weeds and straw residues were removed from the plots, after which ten samples of 0-15 cm plowed layer soil were collected at random, using a stainless steel shovel from 12 plots of the four treatments (three replicates per treatment). To maintain the original structure,the soil deformed from contact with the stainless steel shovel was removed, and the intact soil was put into a hard plastic box to ensure that the soil was not damaged during transportation.After the soil samples were taken to the lab, they were airdried at room temperature. When the soil water content was at soil plasticit(approximately 25%), the soil samples were crumbled gently by hand to 1 cm diameter pieces so as not to be broken further by mechanical stress. After the coarse roots and small stones were removed, the soil samples were air dried and prepared for analysis of the soil aggregates and chemical properties. The bulk densities in the plowed layer soil (0-15cm) were determined at the same time