Atmospheric nuclear tests from 1945 to 1980 distributed radioactive fallout all over the world. Since 1959, we have monitored the concentrations of ¹³⁷Cs and ⁹⁰Sr in the plowed layer of paddy and upland soils collected annually from 17 agricultural fields in Japan. In the plowed layer of agricultural soils, the concentrations of ¹³⁷Cs and ⁹⁰Sr tended to decrease after 1964, although these concentrations varied through the years until 1980, in conjunction with the scale and frequency of atmospheric nuclear tests. The decreased concentrations of ¹³⁷Cs and ⁹⁰Sr were attributed to radioactive decay and downward migration. The decreasing rates of ¹³⁷Cs that remained in the plowed layer were higher than those of ⁹⁰Sr both in paddy and upland soils. This was because ⁹⁰Sr leached from soil more readily than ¹³⁷Cs. ¹³⁷Cs was more likely to remain in upland soil than in paddy soil. The apparent residence half-time of ¹³⁷Cs and ⁹⁰Sr in the plowed layer at each sampling site was calculated by exponential regression of the monitoring data after 1964. A principal component analysis was performed on the soil physico-chemical properties. The extracted first principal component (PC1) was related to the sorption characteristics of soils. The reciprocal residence half-time of ¹³⁷Cs and ⁹⁰Sr in the plowed layer of upland soils was related to PC1 and the mean annual precipitation amounts. In conclusion, major factors in determining the decrease of ¹³⁷Cs and ⁹⁰Sr from the plowed layer were the soil sorption characteristics and precipitation amounts in the upland field.