Verexal implemented in 2025 a series of trials focused on Regulated Deficit Irrigation (RDI). This technique aims to reduce water inputs to the plant without compromising harvest quality. The trials were conducted in an apple orchard across three varieties: 'Aporo', 'Fuji' and 'Bonita'.
The irrigation system consists of a drip network with emitters spaced every 30 cm, each delivering 1 L/h. Scheduling was managed using a combination of capacitive soil moisture probes and water balance modelling, enabling precise monitoring of plant water status throughout the season. Five treatments were tested: a non-irrigated control, a full water comfort treatment based on plant requirements as determined by probe readings, and three deficit treatments corresponding to reductions of 40%, 55% and 70% of the water comfort input. To maintain the integrity of the wetting bulb across all treatments, deficit was applied by reducing irrigation duration rather than frequency. RDI was initiated in June 2025, when crop water demand exceeded rainfall inputs. It should be noted that 2025 proved to be a particularly challenging year for RDI trials. Regular rainfall from June through to harvest limited the number of irrigation events and prevented the onset of sustained water stress periods, which likely attenuated the differentiation between treatments and should be taken into account when interpreting the results.
For the 'Aporo' variety, RDI resulted in a 3 mm increase in fruit calibre and a yield improvement of approximately 3 t/ha compared to the deficit treatments. For the 'Fuji' variety, irrigation reductions had no significant impact on either yield or fruit calibre. For the 'Bonita' variety, no significant difference in calibre was observed; however, yield decreased by 8 t/ha between the full water comfort treatment and the 40% reduction treatment. As a general trend, higher water inputs tend to dilute the organoleptic properties of the fruit, suggesting a potential quality benefit to moderate deficit strategies.
Alongside the RDI trials, Verexal has been testing, since winter 2025/2026, two different compost types aimed at improving soil water retention capacity.
On Wednesday, 1st July, the 2025 results and the 2026 trial protocols were presented on-site in the orchard.