Effects of Root Restriction and Root Pruning on Tree Growth, Yield, and Fruit Quality of 'Nishimurawase' Persimmon

摘要

This experiment was conducted to determine the effects of root restriction and root pruning on tree growth, yield, and fruit quality of 'Nishimurawase' persimmon from 1997 to 2004, The trees were planted in 50 cm-wide, 45 cm-deep trenches lined with either polyethylene (PE) film or non-woven fabric. The rows were 2 m apart and the in-row tree spacing was 1 m, A block of trees were root-pruned annually from 1998. The root pruning was done before bud-break by digging and replacing the soil on two sidesof the trunk at 50 cm to a depth of 45 cm. Root zone of control trees was left untouched until 2004, Root restriction or root pruning significantly decreased tree height, tree spread, trunk cross-sectional area (TCSA), leaf area, number of water sprouts, and fresh weight of above-ground parts. Reductions in tree growth were apparent from the fourth year after planting. The most reduction was found in the trees with non-woven fabric. Cumulative pruning weight was also reduced most in the trees lined with non-woven fabric, followed by the trees with PE film and root-pruned. When excavated in March of the eighth year after planting, it was noted that a few roots were grown through the PE film and the non-woven fabric. Root weight within the restricted zone was the greatest in the trees with PE film, whereas much of fine and medium roots were found near to the cut surface in root-pruned trees. Although not significant, cumulative yield per tree tended to be high in control trees from the fifth year afterplanting while yield efficiency in the trees with non-woven fabric from the sixth. Average fruit weights during the 5 years from the third year were 146 g in the control, 142 g in non-woven fabric, 141 g in PE film, and 138 g in root-pruned trees, exhibiting some negative effects of root restriction and root pruning on fruit size. However, the fruits matured 3, 4, and 2 days earlier, respectively, than those of the control.