This study was carried out to make clear the influence of soil moisture on the harvest and the protein content of soybean by pot culture. The water capacity of the soil used was 38.4%, and the soil moisture was kept constant at 40%, 50%, 60%, 70%, 80%, 90%, and 100% of the water capacity in each plot respectively. The soil moisture was adjusted by pouring water on the pot with a water-can, weighing the pot on a balance. The variety used was "Suzunari".
The results of the experiments are summarized as follows :
(1) The stem grew longer under 90%-70% soil moisture than other percentages.
(2) The weight of seeds was heaviest under 90%-70% soil moisture and became lighter as soil moisture decreased below 70%. There was no difference between plots of 100% soil moisture and those of 60%.
(3) The protein content of seeds was largest under 90% soil moisture and became smaller as soil moisture decreased. There was no difference between plots of 100% soil moisture and those of 70%-60%.
(4) The best growth and the greatest protein content were both obtained under the soil moisture at 90% of the capacity.