Abstract
An estimation formula to determine the time of barnyardgrass leaf emergence was developed to enable application of herbicides at the appropriate time in dry sown paddy fields. The maximum leaf stage of barnyardgrass was investigated under various conditions such as year, cropping season, and field location including the experimental station fields and local farmer’s fields, and examined using the daily mean air temperature of the Agro-Meteorological Grid Square Data System. The results showed that, in dry sown paddy fields, the growth progress of barnyardgrass from the starting point of herbicide application differed from that of plowing. Therefore, the analysis should be done separately according to the starting point, and the effective accumulated temperature -7 degrees is suitable for estimation. Furthermore, considering that the growth may be delayed due to factors other than temperature, we decided to use only the data above the regression line of the measured leaf stage and the estimated leaf stage when creating the estimation formula. The regression equation calculated from the data was used as the estimation formula. Using the estimation formula, we found that in 96% of all the data, the leaf stage difference between the measured and the estimated, was distributed below +0.5, and the measurement rarely deviated greatly from the estimation. Therefore, the created estimation formula was not considered to be a practical problem in dry sown paddy fields under the various conditions in Chugoku area.
