Soil CO₂ Emission And Carbon Balance In The Winter Wheat-Summer Maize Rotation System

Soil respiration and carbon balance in the winter wheat-summer maize system were studied in the suburb of Beijing from 2000 to 2003. The soil respirations under different straw management, irrigation and nitrogen application strategies were measured by soda lime absortion technique. The result showed that, Air temperature and soil moisture were two major environmental factors affecting the soil respiration. The CO2 effluxes from the soil showed exponential responses to the air temperature with significant correlative coefficient (from 0.84~0.87 under different straw management, irrigation and nitrogen application strategies). The Qio of the soil respiration under tradition plant strategy was 2.32. There was no significant correlation between soil moisture and soil respiration, but soil respiration increased if both air temperature and soil moisture shifted to the optimum values; when the soil moisture reached 31%, soil respiration was suppressed. In winter wheat and summer maize growth stages, the highest soil CO2 efflux was 26.4 g CO2 m-2 d-1 and 35.5 g CO2 m-2 d-1 respectively. During crop growth, two soil respiration climaxes were identified. The first climax came from the decomposition of the returned straw and root of the preview crop; the second climax was identified in seeding development stage of winter wheat and in 10 leaves stage of summer maize. The total amount of soil CO2 emission under different straw management, irrigation and nitrogen application strategies were from 3494 to 4113 g CO2 m-2 a-1 Straw amended treatments showed a higher total CO2 emission than no-straw amended treatments; Different nitrogen application rates (600 kg N hm"2 a"1, 178 kg N hm-2 a-1) did not caused difference on total CO2 emission.The carbon budgets of the winter wheat-summer maize system were calculated under the assumption that root respiration was 13.5% of the total soil respiration. The result showed that the winter wheat- summer maize system was a carbon pool of the atmosphere CO2. The carbon pool was bigger in the period of summer maize than that in winter wheat. During winter wheat growth stage, The sequestration of the carbon in the system were from 1663 to3099 kg C hm"2 a"1 under different straw management, irrigation and nitrogen application strategies and sequestration of the carbon in was 3099 kg C hm"2 a"1 under conventional management strategies which were taken by local farmer. The average NPP carbon and soil efflux carbon ratio (NPP/Rs) in tire winter wheat, summer maize growth stages was from 0.90 to 1.16 and from 1.09 to 1.25 respectively under different straw management, irrigation and nitrogen application strategies.Changes of the amount of SOC (soil organic carbon) and SIC (soil inorganic carbon) pool to 1-m depth on a Calcareous Meadow Soil were investigated in a long-term fertilization experiment which have been conducted for 19 years on North China Plain. The applications of the N, P fertilizer increased the amount of SOC, especially in the plowed layer. The content of SIC decreased when the SOC content increased in the plowed layer. The calculation of the amount of SOC to 1-m depth showed that, the SOC storage in the soil layer were improved from 75 t hm"2 to 89 t hm"2 under the normal N, P chemical fertilizer application rates; when the chemical fertilizers were applied with chiken manure, the amountof SOC incresed to 94 t hm-2. The total amount of carbon stored in 0~lm soil layer of the normal N, P chemical fertilizer application rates treatment and the control treatment showed no diference and was 147 t hm-2, 147 t hm-2 respectively.Soil light fraction organic matter was found more sensitive than total soil organic carbon to the different straw management, irrigation and nitrogen application strategies after a 4 year's experiment. The soil light fraction organic matter content increased with the nitrogen fertilizer application rates in a 19 years long term fertilization experiment.