Abstract
In this paper, an estimation method of possible farm operation time for rice-wheat-soybean farming system by hourly precipitation data is opposed. Possible farm operation time by major operation category for the farming system is also estimated by this method. It is verified that the estimation method is appropriate and useful by comparing the estimated possible farm operation time from the actual operation time of harvesting of rice in the study site in past two year. The estimation of past ten years in Ibaraki Prefecture makes it clear that possible farm operation time of rice, wheat and soybean is a major factor of the increase of the farm scale and is unstable in terms of yearly variation.
