Effects Of Fertilization And Water Table On Soil Aggregates And Organic Carbon Fractions In Paddy Soil

A long-term located experiment from1981was utilized to explore the effects of different water table and fertilization treatments on distribution and stability of soil aggregate, organic carbon combined in aggregates and soil organic fractions, Which is also aim at providing a scientific basis for fertilization and irrigation reasonably. Major conclusions were made below:(1)Water stable aggregate of three fertilization treatment under high or low ground water table were dominated by>2mm particle size, the proportion were58.62%～71.29%and68.66%-80.46%, respectively; and the smaller the particle size, the less quantity. The application of crop residue increased the amount of soil water stable aggregate (>0.25mm), aggregate mean weight diameter(MWD), geometric mean diameter(GMD),and decreased aggregate fractal dimension (D). Ground water table affects soil stability significantly, the MWD and GMD of soil aggregate under low ground water table is higher than that under high ground water table obviously.(2)Soil organic carbon (SOC) content is also influenced by fertilization and ground water table. The contents of total organic carbon is14.45～20.46g/kg and14.16～18.88g/kg, the SOC contents of high and normal crop residue application treatments were44%、29%and32%、25%higher than that of mineral fertilizer treatment under high and low ground water table conditions. Water stable aggregate (>2mm) has the highest mass proportion and organic carbon contents among different soil particle sizes, and has the most important contribution to improve SOC.(3) The content of particulate organic carbon(POC) is between6.29～11.77g/kg and increased with the amount of the application of crop residue. And at the same time, POC contents of the three fertilization treatments under high water table are just above those under low water table. Treatments with crop residue have a much higher percentage of POC(fPOC/TOC、oPOC/TOC) than treatments with chemical fertilizer under both the two different water table and especially significant under the low water table. Each organic carbon fraction has a very significant correlation with the soil total organic carbon (TOC) and organic carbon combined in aggregates whose particle size>2mm. Applying crop residue can improve soil TOC and POC both in high water table or low water table district by a large margin, and the application of crop residue seems much more necessary in high water table district.