Physiological Responses of Apple Trees to Different Irrigation Practices

New irrigation practices using controlled soil water deficits offer the opportunity of reducing tree vegetative growth and enhancing fruit quality without decreasing fruit size or yield. We tested partial root zone drying ( PRD ) and deficit irrigation in `Golden Delicious' trees on M9 rootstock, at Summerland, B.C., Canada. There were four treatments: full irrigation ( 100% daily ET replacement ), both sides irrigation ( 50%daily ET replacement ), deficit irrigation ( 1 side, 50% daily ET replacement ) and PRD ( alternating sides, 50% daily ET replacement ). The purpose of this study was to determine how deficit irrigation and PRD affect above- and below-ground physiology of apple trees where the amount of irrigation was the same. Soil water content, stem water potential, stomatal conductance and transpiration were significantly higher for deficit irrigation than PRD irrigation ( P < 0.05) for both years (2003 and 2004). Root dynamics varied among years. For both years, root production was higher in trees under PRD than in trees under deficit irrigation. Root survivorship was significantly higher for trees exposed to PRD treatment than those exposed to deficit irrigation treatment in 2003 ( P < 0.0003), but not in 2004 ( P > 0.662). Stem growth, fruit yield, and fruit quality were generally not affected by treatments in 2003. In 2004, however, fruit yield was 37% higher in deficit irrigation than in PRD ( P < 0.05). Soluble solids and sugar: acid ratio did not differ between these two treatments. For conditions where the amount of irrigation applied was the same, our results suggest that PRD may be less effective than deficit irrigation.