Abstract
To obtain relationships between water depth, and water and soil temperature in a paddy field during rice ripening period, changes in water depth, water and soil temperatures were measured in conventional paddy fields at Ishikawa prefecture, Japan, in 2012 and 2013. A multiple regression analysis was applied to the measured data, and empirical equations were developed for the maximum and minimum water temperature during rice ripening period as a function of water depth, atmosphere conditions, initial water temperature, and days after heading date of rice. Predictions of the equations were in good agreement with the observed temperatures; root mean square errors (RMSE) for minimum and maximum water temperature were 0.49 and 0.81 °C, respectively. Then, relationships between water depth, and water temperature and day water temperature difference were obtained; decrease in 1 cm average water depth decreases maximum water temperature of 0.01±0.10 °C and minimum water temperature of 0.18±0.05 °C, and increases daily water temperature difference of 0.16±0.12 °C. Finally a prediction formula on daily soil temperature difference was developed from an analysis using heat conduction equation of soil and the obtained relationship between water depth and day water temperature difference.
