Studies on the effect of the paddy field soil kept under upland condition on the yield of rice

In Japan, the extent under paddy is approximately three million hectares and the average yield per hectare is about 3000 kg, though high yield gives as much as over 7000 kg per hectare. It is at present a serious problem as to what methods we can use to obtain a high yield of rice. Generally, in well-drained paddy fields where the system of double-cropping is practised, rice is cultivated under a flooded condition in summer, and upland crops such as barley or wheat is cultivated under upland condition in other seasons.