Effects Of Nitrogen Application On The Soil Respiration Of Several Upland Soils And The Carbon Emission From Red Paddy Soil

Carbon cycle in the terrestrial ecosystem has been paid attention due to the increase of the atmospheric concentration of the greenhouse gases such as CO₂ and CH₄. Therefore, carbon cycle in the terrestrial ecosystem has become a hotspot problem in the international cooperation research. China is an agricultural country, which has about 1.33 million square kilometers farmland. The management, such as plough, fertilization and irrigation etc. have not only changed the nutrient cycling in the farmland ecosystem system, but also brought influences to global climate. The research of various factors that influences CO₂ emission from soil will help to valuate the function of agricultural ecosystems as a sink or source of atmospheric CO₂, and the role it plays in the climate changes. The soil respiration in different upland ecosystems in Zigui and the carbon emission from the paddy field in Xianning under the N-fertilized were studied by closed chamber methods. The results showed:1. The soil respiration rates showed a seasonal variation for upland measured in Zigui, Three Gorges region. The soil respiration rates fluctuated with the soil and the atmospheric temperature. There was a significant exponential relationship between the soil respiration rate and the air temperature and soil temperature (in the depth of 5cm and 10cm). Its Q₁₀ value was 1.88².92. There is no significant relationship between soil moisture and soil respiration. The cumulative C emission correlated with N application, and it increased as the increase of N.2. The cumulated carbon for the upland soils varied with SOM, the plants cover, and the cultivation. The cumulative soil respiration for different agricultural ecosystems ranged from 573 gC·m^-2a^-1 to 828 gC·m^-2a^-1. The soil with high SOM content and high N-fertilized had the highest CO₂ emission.3. The respiration rates of the soil-rice system, the interrow and non-crop soil were all influenced by the temperature and the crop growth condition. The rates increased at beginning and then reduced after the peak. The respiration rate was lower in non-crops soil than the rates for soil-rice system and the interrow.4. N application increased the carbon emission from soil. However, N fertilization increased the net primary production (NPP) and the net ecosystem production (NEP) in paddy ecosystems. Accordingly, N fertilization reduced carbon emission from the paddy ecosystems. The value of NPP and NEP were high in the 240 N kg/ha treatment, which was 565.4 gC·m^-2a^-1 and 420.6gC·m^-2a^-1, respectively. The NPP and NEP were...