Investigating effects of over-irrigation and deficit irrigation on yield and fruit quality in Pink LadyTM ‘Rosy Glow’ apple

Fruit production has to be adapted to climate change that is often associated with heat and water deficit episodes. To develop efficient strategies on how to manage commercial orchards under deficit water supply, we need to know the effects of water-stress on crop production. However, when the water supply is abundant apple growers often think that over-irrigation gives higher marketable fruit yield than potential evapotranspiration-based or sensor-based (e.g. tensiometer, dendrometer) irrigation. We therefore aimed to evaluate the effects of three water regimes, namely well-watered (100% of crop evapotranspiration – ETc, WW), 25% of ETc water deficit over the season (water-stressed, WS), and twofold of WW (200% of ETc, 2xWW), on midday stem water potential (SWP), crop yield and fruit quality of Pink LadyTM ‘Rosy Glow’ apples. As expected, SWP was lower in WS than in the others, but both WS and 2xWW decreased fruit yield, although 2xWW tended to increase yield in the >70% color class and ensured quite a constant amount of yield at each picking time. Soluble solid content (SSC) in fruit was higher in WS. As a whole, our results suggest that over-irrigation that is sometimes recommended to keep a safety margin should be considered with caution. Rather, a mild water-stress, between WS and WW in our experiment, may represent a good compromise for a good quality yield.