The Evolution Law Of Organic Matter And Composition Of Humus In Ancient Paddy Soils

The soils organic matter plays an important part in the global carbon cycle. It is not understood that whether the composition of the soil organic matter and its humus evolves to complexity or simplicity as well as the changing process and mechanism in the buried ancient paddy soil after a long-term closure. Therefore, as the research object, the evolvement rule of organic matter and the humus constitution characteristics were studied, the composition and distribution characteristics of organic matter in different soil aggregation were analysed, and the infrared spectral characteristics was discussed in the buried ancient paddy soil at Shanlong village of the Liyang Plain. The project aimed to provide the basis for soil carbon emission and fixation and the carbon biogeochemical cycles. The main research results are shown as follow.(1) The variation of the organic matter ranges from 8.41 g/kg to 24.00 g/kg in ancient paddy soil, and the content of buried ancient paddy soil ranges from 9.5 g/kg to 12.3g/kg. From the profile distribution, the organic matter in buried ancient paddy soil changes as the tendency shows:plough layer> plow pan> waterloggogenic horizon> parent material. Compared with the modern farming paddy soil, the buried ancient paddy soil has lower organic matter with smaller change scope.(2) The organic matter of different diameter aggregate buried ancient paddy soil shows as (5-2mm)> (2-1mm)> (1-0.25mm)> (<0.25mm). From the profile distribution, the organic matter of different grain diameter in the buried ancient paddy soil shows as PA profile plough layer> plow pan, PB profile plow pan> plough layer> waterloggogenic horizon, and PC profile waterloggogenic horizon> plough layer> plow pan> parent material. Compared to the modern farming paddy soil, its organic matter content is larger than that of plow pan, waterloggogenic horizon and parent material in modern farming paddy soil.(3) The average content of different components in the buried ancient paddy soil humus is HA (3.66g/kg)> HU (1.92g/kg)> FA (0.95g/kg). From the profile distribution, the humus of different forms in the buried ancient paddy soil has a smaller content variation and tends to be steady step by step. Among them, the content of humic acid tends to increase as the soil depth increases; the content of fulvic acid in PA and PB profile takes back and is on the rise in PC profile; the content of humin in PA profile decreases firstly and then increases, and decreases firstly, then increases and decreases again in PB profile, and it dramatically declines in PC profile. The HA/FA value of buried ancient paddy soil increases as the soil depth increases. Compared to the modern farming paddy soil, its HA/FA value is lower.(4) The average content of combined humus of the buried ancient paddy soil is H1 (12.75g/kg)> H2 (4.07g/kg)> H3(0.42g/kg), showing the largest relative amount appears in the loose combined state (58.36%), the next is tight combined state (52.52%) and the then stable combined state (9.82%). From the profile distribution, the buried ancient paddy soil has a larger content variation in the content of humus in different combined state. The loose combined state of PA and PB profile is on a declining curve, the stable combined state is on the rise and the tight combined state decreases.(5) The functional group of buried ancient paddy soil mainly concentrates on the halogen compounds and inorganic compound. The organic matter has a great impact on the of buried ancient paddy soil. The medium wave in ancient paddy soil is 1882 cm-1 and the absorption peak wakens after removing organic matter. The medium wave of the buried ancient paddy soil is 1631-470cm-1, and forms to be benzene ring and olefinecompound with increasing aromatization and reinforced binding force of halogen and inorganic compound. According to the first-order reciprocal, the buried ancient paddy soil has little difference from the modern farming paddy soil. After removing the organic matter, the value of FD shows a difference:before removing organic matter> after removing organic matter and their FD peak value both decline.