In order to clarify the infection factors of Japanese pear stunt which has increased in recent years, the comparison investigation of six ’Kosui’ gardens including remarkable diseased garden A and rarely diseased garden C by soil diagnosis was done. Effective soil layer and rooting zone of garden C were the most deep(80cm), however effective soil layer and rooting zone of garden A were the most shallow(30cm). In all gardens, soil pH, content of base and electric conductivity of the medium and lower soil layer were high, so the damage of the root was feared . Garden A was the most remarkable trend in all gardens. In garden A, impermeable clay layer which blocked the downward movement of the base was located in the medium and lower soil layer, and this clay layer located in the shallowest in all gardens. This impermeable soil layer in garden A might be responsible for the remarkable trend. In addition, nitrogen content of the tree leaves in garden A was less than the other gardens. The low nutrient uptake of the tree in garden A might be due to the shallow effective soil layer and the shallow rooting zone. The soil moisture in garden C showed less fluctuation, and garden C kept appropriate soil moisture in long duration. The soil moisture in other gardens showed more fluctuation, and these gardens were under excess soil moisture condition in longer periods. It was suggested that the occurrence of the disease of pear trees could be related to the damaged tree vigor caused by the shallow effective soil layer, the shallow rooting zone, the large fluctuation of wet and dry soil, and the base accumulation in the impermeable soil layer.

View full abstract