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 (668KB)
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7,505,000 Yen (FY1998; 2,515,000 Yen)
Carbon budget, Single-cropping, Double-cropping, Soil respiration
Carbon dioxide evolution rates from a double cropping, upland rice and barley, field were determined in central Japan from June 1992 to May 1994, and regression models were developed to predict soil respiration rate. Diurnal patterns of hourly soil respiration rates (SRh) showed similar trend with those of soil surface temperatures. Daily soil respiration rate (SRd) obtained by integrating SRh varied 0.3 to 15.6 g CO2 m-2 d-1 for the two years. In summer cropping period, SRd had positive correlation with daily mean soil surface temperature and negative correlation with volumetric water content in soil. Moreover, this relationship was able to be expressed as a multiple-factor model with an Adj-R2 of 0.925. On the other hand, in winter cropping period, SRd was able to be represented by a single factor model using soil surface temperature and an Adj-R2 value was 0.854.
Carbon dynamics and budgets were investigated in upland and paddy agricultural ecosystems in Japan. The experiments were carried out in upland single- and double-cropping fields and paddy single-cropping fields in central Japan, between May 1991 and April 1997. Carbon budgets were different between the upland crop field and the paddy crop field. The annual carbon balance was estimated to be -270¡Á-320 gCm-2 for the upland single-cropping field, -160¡Á-270 gCm-2 for the upland double-cropping field, and only -20 gCm-2 for the paddy rice single-cropping field. These results suggest that effective agronomic measures are needed to maintain the carbon balance in prevailing upland agro-ecosystems in order to sustain soil fertility, and the upland agro-ecosystems may contribute to the increase in the carbon dioxide concentration of the atmosphere as the carbon accumulated in the soil is constantly being released in the atmosphere, and improved management is capable of increasing C levels on existing agricultural soils in Japan. On the other hand, the carbon balance for the paddy agro-ecosystem was in good agreement, sometimes resulting in a positive increase in carbon. This is caused by a decrease in the heterotrophic respiration in the soil deoxidized under the flooding water and carbon fixation by photosynthesis of algae. The paddy rice field may be well-carbon balanced agricultural system and this may permits a sustainable land use for long period more than hundreds years.