In the field of Kuroboku soil with humus top layer (Komekamito) at the Metropolitan Tokyo Agricultural Experiment Station (Tachikawa City) we investigated, in connection with the continuous application of organic matter, the effects of rotary tilling over a period of 20 years on the physico-chemical properties of surface soil and on crop yields. The results showed that the total carbon and total nitrogen contents of soil increased with the application of organic matter, but the rate of increase was smaller in tilling plot. In the plot where chemical fertilizers were continuously used, we found no effect of tilling on T-C and T-N. Available soil moisture content tended to decrease gradually over 20 years especially, the gaseous phase ratio at pF 1.5 tended to increase gradually, however, we observed a trend, as the years passed, that there were decreasing differences among the plots. Mineral nutrient content of the soil hardly differed between tilled and untilled soil, but it increased greatly in the plots where organic matter has been used repeatedly. Similarly to T-N of soil, available P2 05 increased with the continuous use of organic matter, but the rate of increase was lower in the tilled than in the untilled plot. Rotary tilling had little effect on the yields of cabbage and radish, though they were slightly higher with the continuous use of organic matter and the practice of rotary tilling. Even when chemical fertilizer alone was used, yields were higher when tilling was employed. Rotary tilling did not decrease crop yields. However, we noticed the formation of furrow pan due to rotary tilling, a tendency that was especially strong when only chemical fertilizers were used. Therefore 20 years of crop cultivation had no impact on the yields of cabbage and radish, but soil management that does not allow the formation of furrow pan is necessary, and for that reason the application of organic matter is important.
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