Farm work so called “shirokaki”, of harrowing and leveling of watered paddy field to pulverize and knead the soil, which is practiced prior to transplanting, is found to introducee air into the soil, and leads to high percentage and larger amount of oxygen in the soil, but the oxygen is exhausted sooner than that in the field without “Shirokaki”It was evidently observed on the field supplied with inorganic fertilizers that the cultivation also introduces air into the soil, but on the field supplied with organic manures the reverse relation is observed, because cultivation, providing oxygen into the soil, may stimulate rapid exhaustion of oxygen by micro-organisms.