Effects of root pruning and supplemental irrigation on net carbon exchange, transpiration and water relations of peach

Field studies were conducted at the Horticulture Research Centre in Carbondale, III. in 1998, 1999 and 2000 to evaluate the effects of root pruning and supplemental irrigation on net carbon exchange (NCE), transpiration (E) and leaf water potential (W) of mature 'Loring'/Lovell peach trees. Trees were root pruned parallel to the row, 60 cm from the centre of the trunk on both sides to a depth of 30 cm at petal fall (PF), 3 weeks after petal fall (PF+3wk), 6 weeks after petal (PF+6wk) or not root pruned. Half of the trees were provided with supplemental irrigation at the beginning of stage III of fruit growth. NCE and E were measured twice: 1) beginning of stage III of fruit growth (twelve weeks after petal fall), and 2) after fruits were removed from the trees (seventeen weeks after petal fall). Leaf water potential (psi) was measured once a season during stage III of fruit growth (1997, 1999) and after harvest (1998), in two instances during the course of the day (predawn and mid-day). Date of root pruning or supplemental irrigation did not affect NCE at PF+12wk or PF+17wk, in any of the years. In 1999, E at PF+12wk increased by 100%, 120% and 110% for PF, PF+3wk and PF+6wk root pruning treatments, respectively. In 1998, at PF+17wk E increased by 91% for PF root pruning treatment and was reduced by 10% and 7% by the PF+3wk and PF+6wk root pruning treatments, respectively. In 1997, supplemental irrigation increased psi(pre-dawn) sampled at PF+12wk in the trees that had been root pruned. In 1997, supplemental irrigation increased psi(mid-day) by 6%. In 1999, psi(mid-day) increased as the timing of root pruning moved from PF to PF+3wk then levelled of by PF+6wk (P < 0.0948). In 19999 supplemental irrigation decreased psi(pre-dawn) 8% (P < 0.0576).