(321) Rapid and Differential Rates of Root Browning in Apple Trees under Different Irrigation Treatments

Abstract

As roots change color from white to brown, their absorptivity for water and nutrients typically diminishes. The effects of irrigation on root pigmentation were studied during 2003 and 2004 in Summerland, British Columbia, using an experimental orchard of `Golden Delicious' apple trees on M9 rootstocks. Root pigmentation was monitored weekly over the growing season using a minirhizotron camera inserted into clear plastic tubes in the root zone. Each tree had two emitters, one on either side of the bole and ≈30 cm from the trunk. Four irrigation treatments were tested: full irrigation with replenishing 100% of daily evapotranspiration (ET) on both sides of the tree (100% both), 50% ET irrigation on both sides (50% both), irrigating alternating sides of the tree with 50% ET (50% alternating) and one-sided irrigation at 50% ET (50% one-side). The 50% alternating irrigation treatment simulated the irrigation practice of partial root zone drying where irrigation was alternated about weekly from one side of the tree to the other. Root pigmentation was remarkably fast among these trees, with median days to browning ranging from 4 to 10 days among treatments. For 50% one-side trees, root pigmentation on the dry side of the tree was much faster than roots on the wet side (4 and 7 days, respectively; P< 0.007). Otherwise, no additional significant effects of irrigation on pigmentation were detected.