Characteristics and estimation of CH₄, N₂O emissions from cold paddy field in the Sanjiang Plain

CH₄ and N₂O emissions from the cold paddy field were measured with static-closed-chamber and GC (Aglient 4890) by the continuous experiments in the Sanjiang Plain in Heilongjiang Province in Northeast China from 2003 to 2006, the characteristics of CH₄ and N₂O emissions from the paddy field were defined, and the main influence factors that the paddy field CH₄ and N₂O discharges were analyzed at the same time. The results show that it has obvious characteristics of seasonal variations that the paddy field CH₄ and N₂O are discharged, it is strong CH₄ source during the waterlogging period of rice paddy, CH₄ flux drops notably until paddy field drains off water, and CH₄ flux is faint or weak to absorb in whole fallow period. Unimodal type of CH₄ emission changed with the changes of rice plant growths and leaf area index. N₂O emission is very small because the rice pours water continuously while growing, and the weak absorption phenomenon appears sometimes at temperature drops and in cover of ice and snow while lying fallow at the same time. It generally appears N₂O discharge peak after using the base manure and topdressing, and it always presents discharging weak peaks when the water level declines during the growing period. Temperature and moisture are two of the important factors to influence paddy field CH₄ and N₂O emissions, but the water depth and gas fluxes do not have obvious relevance. The rice plant influences the gas fluxes greatly. The CH₄ emission is promoted and N₂O emission is reduced because of the absorption of nitrogen and impact on soil structure of roots of the rice plant; During in growing season, it influences and differs greatly the paddy field CH₄ emission to use the nitrogen, but promotes the emission of N₂O greatly. According to the emission rates of CH₄, N₂O and the area of the paddy field in Sanjiang Plain, the total amounts of emissions of CH₄, N₂O were estimated and they were 0.1035 Tg/a and 0.0021 Tg/a, respectively.