The long-term effects of regulated deficit irrigation (RDI) on Navelina orange trees was examined in Spain over a five-year period. Dr. Maria Gasque and co-workers in Valencia conducted the trial and results were recently reported in the scientific journal Agricultural Water Management.
Three irrigation treatments were applied during five consecutive years (2007–2011). The control treatment without water restrictions was compared with the two RDI treatments, in which the water reduction was applied for about seven weeks during summer, from mid-July to early September (initial fruit enlargement phase). The treatments in the early years of the trial were 40% and 60% of the full irrigation.
The overall results showed that the RDI treatments did not cause negative effects on either quality or yield, given the that trees were not pushed too far into stress. The results showed that the irrigation water savings were between 12% and 27%, which resulted in only a slight reduction in average fruit weight in the RDI treatments, in the more restrictive cases, which was balanced with a higher yield.
It is interesting that this study showed that there was no difference in fruit quality between the treatments. They measured peel %, juice %, TSS, TA, a maturity index and vitamin C content and no differences showed between the RDI treatments. The results from this study is in contrast to many other published studies, which have shown that RDI can benefit fruit quality (i.e. increase TSS).
The authors suggest the reason this experiment did not affect the TSS or TA of the fruit was that these other studies could have had a longer stress period or suffered higher levels of water stress.
Gasque M, Martí P, Granero B and González-Altozano P. 2016. Effects of long-term summer deficit irrigation on ‘Navelina’ citrus trees. Agricultural Water Management Vol169, pp. 140–147