Abstract
We investigated the effect of localized deep application of compost using a labor-saving excavation machine on the yield and root growth of the Japanese pears tree, ‘Kousui’, which shows decreased yield with aging of the trees.
1. A significant positive correlation between fruit yield and weight of fine roots with a diameter of 1 mm or less was observed in 10 alluvial soil fields of matured Japanese ‘Kousui’ pear trees in Saitama Prefecture.
2. Twenty liters of compost was applied without mixing the soil in eight holes dug 1.5 m away from the trunk of ‘Kousui’ trees, which had shown reduced yield and root growth. Holes were created using a hole digger machine (tractor-attached type). The fruit size and yield of the treated trees were increased one year after compared with those of control trees. The same results were obtained two and three years thereafter. The root growth after treating with compost was analyzed using root analysis software ‘RHIZO’ (Regent Instruments inc). The total length of roots with a diameter of 0.5 mm or less was increased about 3 times compared with that of control trees, 1, 2 and 3 years after treatment.
3. After digging a hole near the rooting zone using the hole digger machine, the application of compost to the hole replacing the soil dug out sharply increased the total length of the fine roots ten-year-old ‘Kousui’ trees after two years.
4. Spot application of compost using the labor-saving hole digger machine to Japanese pear trees showing lower yields, sharply increased the quantity of the fine roots, resulting in increased fruit size and yield.
