Research On The Emission Of Volatility Sulfur Compound From Soil-Plant Ecosystem

In order to understand the approaches of biogenic sulfur gases emission from soil-plant ecosystem and primary emission mechanism and flux, first using the laboratory incubation method, to investigate the main factors influencing the sulfur gases emitted from soil in detail. Further, soil sulfur emission mechanism was analyzed qualitatively and quantitatively by orthogonal design and multinomial regression for experimental results. Furthermore, reaction kinetics theory was applied to discuss the superficial kinetics pattern of sulfur gases emission. To reduce a great deal of measure work, establishing mathematical model of soil sulfur emission using BP learning algorithm in artificial neural network (ANN), so that soil sulfur emission can be forecasted and analyzed. On the base, measure and analysis work were expanded to situ farmland, to understand sulfur emission mechanism and flux of actual soil-plant ecosystem. The whole research work was divided into three parts: researching by laboratory incubation method, measuring the emission flux of situ farmland and establishing mathematical model.1. The study of biogenic sulfur gases emission from rice paddy soils using the laboratory incubation methodTop-soil samples of rice paddies were collected, various sulfur source was respectively applied into the incubated soil samples in laboratory, and the emission rates of sulfur gases from these incubated soil samples were measured with a gas chromatograph equipped with a double-flame photometricdetector (FPD) operating in the sulfur mode. The detected sulfur gases were: carbonyl sulfide (COS), carbon disulfide (CS2), dimethyl sulfide (DMS), methyl mercaptan (CH₃SH), hydrogen sulfide (H₂S), and dimethyl disulfide (DMDS). The results show that these sulfur gases emitted from soils were identified as products of microbial decomposition of sulfur-containing amino acids, diethyl sulfate and reduction of sulfate. These applied sulfur sources may be the precursors of biogenic sulfur gases emitted from soils.The influences of environmental factors of soil incubation: the amount of applied sulfur sources, atmosphere conditions on the top of incubation bottle, soil water ratio, light regime, incubation temperature, soil pH, soil oxidation-reduction potential (Eh), the application of carbon source and nitrogen source and types of soil on the emission of sulfurgases from soil were investigated in detail. The results indicate that these environmental factors have different effects on the emission of sulfur gases from soil. The emission of some kinds of biogenic sulfur gases exists significantly linear correlation with the amount of applied sulfur sources added to soil. The lnarithmic values of emission rate of biogenic sulfur gases also show linear correlation with the incubation temperature of soil. The emission rate of biogenic sulfur gases reaches the maximum under a certain of condition of soil water ratio, soil pH, soil Eh, light regime. The sulfur emission rate from rice paddy soils was great higher than that from dryland.The orthogonal design experiments show: temperature, soil moisture level, soil pH have more important influence on sulfur gases emission.The Multinomial regression indicate that interaction among environmental factors obviously influence the sulfur gases emission from soil. Different environmental factor shows different importance for different kind of biogenic sulfur gas. Using regression equation of interaction, forecasted precision of sulfur emission was higher.The reaction kinetics theory was applied to discuss several groups of typical curves of sulfur gases emission. The results indicate that the superficial kinetics pattern of sulfur gases emission were consistent with the first order continual reaction kinetic model, designing program optimized kinetic constant of reaction. This study could interpret properly some measure results. 2. The measurement of sulfur emission flux from situ farmlandSulfur gases emitted from rice and wheat fields during the whole cropping period were measured with a closed chamber method. The trace sulfur gases were enriched with adsorption and condensation method. Three speciates of biogenic sulfur gas emitted from rice and wheat fields was detected: COS, DMS and CS2.COS comprised the major part of the sulfur emission from rice fields. The wheat fields and plant can absorb COS gas and emit DMS and CS2 gases. The emission flux of biogenic sulfur gas was different in the different cropping period of rice and wheat, this indicates that the emission flux were greatly influenced by the physiological activity of rice and wheat growth.The environmental factors: light, temperature, soil pH and Eh have important influence on sulfur gases emission from rice and wheat fields. Soil pH and Eh status of rice field were controlled mainly by water and fertilization regime. Water and fertilization regime have indirect effects on sulfur emission from rice fields. The analyse of diurnal variations of sulfur emission from wheat fields show that: COS and CS2 emission rates...