The change of soil condition by rotation from paddy to other crops and examination of the method of farm land consolidation

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The study is made up of two sections which are undermentioned.(1) On the problems of the water requirment of rotational paddy fields. At first on the problem of water requirment of rotational paddy fields, effective soil layer of rotational paddy field, soil moisture extraction pattern, amount of each irrigation and soil moisture content when plant had to be irrigated were examined. Consequently, for the existence of plowsole effective soil layer of rotational paddy field is shallow and soil moisture extraction pattern becomes shallow layer extraction pattern. For the reason it became clear that value of total readily available moisture became small, and interval of irrigation became short and the number of times of irrigation became large. And when plants are cultiwated in the rotational paddy field, it is necessary that soil moisture is wet when plants are irrigated.(2) On the problems of the drainage of rotational paddy fields. In oder to predict the surface drainage discharge of a rotational paddy field, we proposed the runoff simulation model, which was composed of the eqeations of water balance and motion in ridge soil and furrow space. And by applying it to the observed runoff data of test fields, the value of the model parameters was able to be identifiedand the relation between the value of the parameters and soil permeability of test fields was examined. Furthermore, as a result of simulation by this model, the runoff coefficients of a design rainfall was able to be obtained.