Effects of Root Restriction on Tree Development in Ponkan Mandarin (Citrus Reticulata Blanco)

Abstract

The effects of root restriction, induced by root restriction bags, was evaluated on `Yoshida' Ponkan mandarin (Citrus reticulata Blanco). Trees were planted in 0.02-m3 volume root wrap bags (RWBs), which were made from woven polystyrene fiber, or root control bags (RCBs) made from nonwoven UV-stabilized Duon polystyrene fibre with plastic bottoms. A direct soil planted, nonrestricted root treatment (DPC) was included as a control. After 3 years, reductions in height (14% to 29%), canopy volume (66% to 43%), girth (10% to 22%), and leaf area (8% to 12%) were recorded in both of the root restriction treatments. Greater reductions occurred in the RWB treatment. Photosynthesis, transpiration, water potential, and leaf carbohydrate content were not affected by root restriction although soil moisture content was lower in the root restricted treatments. Fruiting efficiency (i.e., number of fruit per unit volume of tree canopy) improved only in the RWB treatment over the control. Total soluble solids and the fruit color index were enhanced by root restriction.