Carbon dioxide evolution of an upland rice and barley, double cropping field in central Japan

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 a similar trend with those of soil surface temperatures. Daily soil respiration rate (SRd) obtained by integrating SRh varied from 0.3 to 15.6 g CO₂ m^-2 for the 2 years. In the summer cropping period, SRd was positively correlated with daily mean soil surface temperature and negatively correlated 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 the winter cropping period, SRd was able to be represented by a single factor model using soil surface temperature with an Adj- R² of 0.854. Based on these relationships, seasonal changes in soil respiration rate were estimated. Total soil respiration rates in 1992 and 1993 estimated for the summer cropping period were 1260 g CO₂ m^-2 and 1094 g CO₂ m^{- 2}, and for the winter cropping period 624 g CO₂ m^-2 and 676 g CO₂ m^-2 respectively. It was considered that the lower values during the summer cropping period in 1993 depended on lower soil surface temperature and higher soil water content.