2022 Volume 21 Issue 3 Pages 279-286
Chestnut trees in a new orchard, which have been transplanted from mountain hills and rice fields, are showing an increased number of freezing injuries. A combination of high ridge cultivation and black sheet mulching has become popular to reduce freezing injuries. In this study, we investigated the effects of soil hardness and microclimate around trees on the freezing temperature of shoots. We also studied factors responsible for reducing freezing injuries when high ridge cultivation and black sheet mulching were used. Soil hardness increased with depth on the flat ridge, while no such change was noted on the high ridge. Tree vigor on the high ridge was stronger than that of trees on the normal flat ridge. Regardless of the surface color of sheet mulching, it reduced the soil moisture content in the high ridge more than the soil in the non-mulched high and flat ridge. However no effect of any treatments were observed on the water content of shoots from February to April. The freezing temperature of the current shoot buds, in mid-February, was decreased on black mulching, but did not decrease on white mulching compared with the normal flat ridge. On the normal flat ridge, 25％ of trees died due to freezing injuries whereas no trees died on the high ridge, regardless of mulching. These results indicate that the popular solution to freezing injuries ameliorated physical conditions of the soil and kept it dryer than with other treatments. Consequently, high ridge cultivation and black mulching ensure a higher freezing tolerance than the conventional flat ridge.
