Response of young ‘Star Ruby’ grapefruit trees to regulated deficit irrigation with saline reclaimed water

• Regulated deficit irrigation (RDI) allowed water savings about 13%.
• RDI with/out reclaimed water did not affect gas exchange parameters.
• RDI with/out reclaimed water did not affect yield and fruit quality.

In this study, the physiological and agronomic effects of irrigating a commercial young grapefruit orchard with saline reclaimed water (RW) combined or not with a regulated deficit irrigation (RDI) strategy were analyzed over three consecutive years. Two water sources, transferred water (TW; ECw ≈ 1.3 dS m−1) and reclaimed water (RW; ECw ≈ 3.0 dS m−1) were used, and two irrigation treatments, a control treatment (irrigated 100% of the crop evapotranspiration; ETc) and a RDI treatment (irrigated 50% of ETc during the 2nd stage of fruit growth) were performed. Results evidenced that RW, especially under the RDI strategy, increased the soil salinity, particularly in summer due to a greater evapotranspirative water demand. However, soil salinity did not increase, as salts were likely to be washed by rainfall. Stomatal conductance and net photosynthesis were not affected by the use RW combined or not with RDI strategies. However, RDI strategies worsened the tree water status regardless of the type of water used; TW or RW, although re-watering increased rapidly the stem water potential up to values similar to that of the control trees. The RDI treatment, which allowed reaching an average annual water saving of 13.2%, combined or not with RW, did not negatively affect vegetative growth, yield and fruit quality, which might be of great economic and competitive significance for agriculture. The combination of RW and RDI did have not affect negatively the soil and young grapefruits, but further research focused on a longer term should be carried out since detrimental effects might appear.