抄録
The great majority of upland fields in Japan are on plateau and hill-side where water permeability is high. Accordingly, upland crops frequently encounter drought injury in the dry season from July to August. To be resistant to drought injury, it is essential for upland crops to have roots deep in the soil where their roots can absorb nutrients and water effectively. This experiment was conducted to clarify that the root distribution of upland-cultured paddy rice (var. Myojoo) in the soil was influenced by tillage methods. The tillage methods used in this experiment are as follows: tillage by disk harrow at a depth of 10 cm after Mouldboard plowing at a depth of 25 cm, tillage by Rotavator at a depth of 17 cm, tillage by Screwvator at a depth of 30 cm. The results obtained are as follows: 1. Root distribution in the soil was influenced by tillage depth and physical soil properties. In Screwvator tillage, the roots distributed from the shallow layer to the deep layer of soil. In Rotavator tillage and in combination of disk harrow with Mouldboard plowing, the roots distributed only in the shallow layer. Soil strength by Mouldboard plowing was almost the same with the other tillage methods up to 10 cm from soil surface, but it was higher in the deeper layer than 10 cm. 2. There was no difference in top dry weight of upland-cultured paddy rice at 8th leaf stage between Rotavator tillage and Screwvator tillage. In Moudboard tillage, top dry weight was less than that in the above-mentioned tillage methods. This was due to high soil strength preventing the root growth. 3. Top dry weight at heading time was the greatest in Rotavator tillage, the second in Screwvator tillage, the third in Mouldboard plowing. This tendency continued to maturity stage. Reduction in top dry weight in Screwvator tillage was due to the penetration of roots into deep soil layer lacking in soil moisture. 4. Correlation coefficients between top dry weight and root dry weight were significant (r=0.733).
