Abstract
To determine the optimal soil moistures at various growth stages of a Japanese pear (Pyrus serotina Rehd.) cv. ‘Kosui, ’ water content of the tree body was estimated by daily measurement of diameters of stem and fruit under various soil moisture conditions. The thresh-old values of the tension of soil moisture which did not give any severe water stress to the tree depended on the growth stages of fruit development; pF 2.40 at the cell division stage; pF 2.35 at the initial growth stage; pF 2.24 at the slow growth stage; pF 2.48 at the latter growth stage; and pF 2.29 at the full ripe stage. After the harvest of fruit, the value was pF 2.48. Photosynthetic rate declined 40% or more when the tension of the soil moisture became higher than pF 2.3. It is concluded that the threshold tension of soil moisture without severe water stress to the tree is pF 2.2-pF 2.40.
