水田の水・熱収支に関する調査研究

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Daily water consumption and seepage of a rice paddy field with acreage of 3086m^2 in Noichi Town was investigated from April 10, 2001 to August 6, 2001. The soil of the paddy field is highly permeable, and 'Shirokaki' (paddling) was performed elaborately before 'Taue' (rice seedlings transplanting). The result is as follows. (1)Since the soil is highly permeable, a lot of seepage into the ground was observed after the development of crack by 'Nakaboshi' (intermittent full drainage of paddy field water) perfomed from the end of May to the first one third of June. (2)It is found that water temperature of the paddy field near water inlet are lower and temperature far form inlet is higher. (3)At the earlier stage of rice cultivation, the water temperature of the paddy field was higher than the air temperature, but at the last stage, both temperatures approached closer. (4)The seepage given by seepage meter varies much, but the seepage values calculated from daily water comsumption (mm/d) minus estimated evapotranspiration by Penman' s method gave rather stable seepage values. (5)The interrelationships between large scale pan evaporation (class A pan), small scale pan evaporation (with 20cm diameter) and Penman's potential evapotranspiration were investigated by simple regressional analysis. The result were not so remarkable and not so highly interrelated. (6)After 'Nakaboshi', it was hard to calculate effective rain, because if all the water percolated into the soil should be counted as effective rainfall, we have enormous effective rainfall after Nakaboshi because of improved permeability.
2002-12-25

水田の水・熱収支に関する調査研究

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