Potential Of Respiration And CO₂ Evolution From Different Samples Of A Paddy Soil Under Different Long-term Fertilization Treatments And Aerobic Incubation

The soil carbon pool is the biggest one in the earth surface system and the soil organic carbon (SOC) plays an important role in greenhouse effect and global climate change. Paddy soil is especial artificial marsh soil of china, area is 2.987* 10⁷ hm², produced quarter of food supplies, played an important part on agriculture production. Some researches showed that the SOC in topsoil of paddy soils was higher than that of the dryland. The SOC of paddy soils has been rising in resent years in china. Soil respiration and CO2 evolution has been considered as a active and rapid CO2 gas exchange pathway from the terrestrial ecosystem between soil and atmospheric interface. The soil potential of organic carbon mineralization and CO₂ evolution exchange has been often studied by using laboratory incubation of disturbed soil samples. The protection of particle-size fractions are the keys in soil carbon circling. Therefore, study on undisturbed soil columns and bulk soil samples were collected after rice harvest from a long-term typical paddy soils in the Tai Lake region, Jiangsu, China. Comparison on the two foster condition difference in organic carbon minralization and CO₂ evolution, to provide science data on reducing CO₂ flux from paddy soils. The main results showedas follows:1 The dynamics of microbial C and N had differences between undisturbed and disturbed column samples. Microbial C ranged from 115.1 mg·kg^-1 to 599.9 mg·kg^-1 and 316.0 mg·kg^-1 to 539.7 mg·kg^-1,and microbial N ranged from 6.1 mg·kg^-1 to 24.9 mg·kg^-1 and 7.9 mg·kg^-1 to 30.6 mg·kg^-1 in undisturbed and disturbed column samples. In aerobic incubation, microbial C were fallen follow the time, but microbial N were firstly risen, and then fallen to reach tranquilization. In Undisturbed and disturbed column samples, LOC were firstly risen, and then fallen, ranged from 7.25 g·kg^-1 to 15.69 g·kg^-1 and 7.32 g·kg^-1 to16.84 g·kg^-1. The dynamics of LOC/SOC were the same with LOC.2 In the experiment pot of undisturbed and disturbed column samples, CO₂ total flux ranged from 2.2 CO₂-C mg·kg^-1 to 4.5 CO₂-C mg·kg^-1 and t3.4 CO₂-C mg·kg^-1 to 15.4 CO₂-C mg·kg^-1. In disturbed column samples, the differences of different fertilization: CF > CFM≈NF>CFS. In undisturbed samples, the differences of different fertilization: CF > CFS>CFM>NF. On the condition of undisturbed column samples, soil respiration was far lower than disturbed samples and the differences of different fertilization were more prominence.3 SOC mineralize dynamic curve of disturbed and undisturbed samples both had three phases: the first phase was speed high and time short, the second phase was speed fall and time long, the third phase was speed low and steady. In different fertilization, disturbed samples had differences in the first phase, but undisturbed sampleshad differences in all the three phases. In the three phases, soil respiration rate of undisturbed samples were all lower than disturbed samples, and differences in fertilization had evidence increased.4 The microbial metabolic quotient and mineralization rate of disturbed samples were 3-7 times and 3-6 times higher than undisturbed samples,and the differences of different fertilization were more prominence than undisturbed samples. Mineralizable carbon of soil protection was sixth to third of microbiology mineralizable carbon, was 1.5% to 2.1% of SOC. This implied that disturbed soils decreased the ability of microorganism making use of SOC on the condition of different fertilization. In undisturbed column sample, soil protected sizable microbiology mineralizable carbon of paddy soil. Therefore, microbiology mineralizable carbon could not all be the fountain of CO₂ evolution. That could be an important mechanism of paddy soils reduceing greenhouse gas evolution.