2021 Volume 20 Issue 3 Pages 305-313
We revealed the effectiveness of new root loosening treatments (RLT) by a fork-shaped bucket (fork treatment), an inverted U-shaped bifurcated chisel (breaker treatment), a manual hoe for a tea garden (handhoe treatment), and a whole-layer loosening subsoiler mounted on a tractor (soil plowing treatment) on amelioration of freezing tolerance of young chestnut trees. The RLT-applied trees with fork and/or breaker attachment did not develop freezing injury compared with those receiving conventional RLT, even under the conditions where the control trees developed severe injury. Therefore, these 2 kinds of new RLT are suitable for improving RLT. Soil plowing by subsoiler attachment also ameliorated freezing injury compared with the control, although the effects were weaker than with conventional RLT. The manual RLT using a hoe decreased the non-freezing temperature of dormant buds the same as conventional RLT using a machine regardless of the number of applications, and the temperature was markedly lower than in the control. Moreover, this manual RLT suppressed the development of freezing injuries even in frequently injured orchards converted from rice fields. Thus, manual RLT is suitable for narrow orchards, where machines cannot enter. The mechanisms to prevent freezing injury were mainly associated with the low water content of the tree, although it was suggested that other physiological factors were also influential. RLT in November may prevent freezing injury development, which will be induced by a low temperature in early winter (hardening period), accelerating freezing tolerance development more than conventional December and/or January RLT. As mentioned above, the new RLT and season will have a greater effect than conventional RLT. These new RLT will expand suitability to a wide range of orchard conditions and tree heights.
