The authors have reported in their previous papers that the growth of rice plant was different by affect by tilling with a power-tiller compared to that with a plow and a harrow. The amount of NH3-N increased and the soil became reductive, because, power-tiller tilling made small clods in the soil more than a plow and a harrow. Such a phenomena was promoted under higher temperatures and on paddy soil which was apt to become reductive. As the results of NH3-N increase, (A) the number of spikelet per hill increases, (B) occasionally ripening of grain is retarded, with the increase in the number of spikelet per hill, (D) ripering of grain is protracted by reductive conditions of the soil, (C) those effects become more intense when the soil is reductive from early growing stages. According to the mutual relations of the facts guessed above the growth of rice plant in the paddy field tilled with a power-tiller and in that tilled with a plow and a harrow was observed as follows: In the low temperature year: The yield of grain increased mostly on behalf of the effect of A in the paddy soil which did not become reductive conspicuously; in case of paddy soil which was apt to be reductive, the yield of grain did not increase because of the effects of B and D. In the high temperature year: In case of paddy soil, which does not become reductive, the increase in yield of grain was arrested chiefly in behalf of the effects of A and B, and partly because of D; when the soil is apt to become reductive, the yield of grain decreased on behalf of the effects of D or C; moreover, in case of soil where it is apt become to reductive from an early stage, the yield of grain decreased on behalf of the effects D and C. The number of brown rice grains produced according to lowering of Eh value in the soil, during the stage of young ear formation when Eh6 value was kept higher than at 100 mV. On the contrary, when Eh6 value ran below 100 mV, the number of brown rice grains yielded decreased in accordance to lowering of Eh value in the soil.