Irrigation is the best strategy to reduce the adverse effects of water stress on almond trees
[Prunus dulcis (Mill) D.A. Web] and improve their productivity. However, in the current context
of climatic change, in which the amount of water available for irrigation is increasingly limited,
deficit irrigation (DI) strategies have become essential in the almond orchards of southern Europe.
Other practices, such as the foliar application of reflective compounds, are being implemented. A
three-year experiment (2019–2021) was set in a factorial design in which the effect of regulated deficit
irrigation and foliar kaolin spray was evaluated on physiological (predawn leaf water potential,
relative water content, leaf area, leaf gas exchange, and chlorophyll fluorescence) and agronomic
parameters (yield, yield components, and water use efficiency (WUE)). The treatments include full
irrigation (FI), which received 100% of ETc (crop evapotranspiration) during all irrigation seasons;
regulated deficit irrigation (RDI), which received 100% of ETc until the kernel-filling stage, reducing
the application to 35% ETc during the kernel-filling stage until harvest; and both irrigation regimes
combined with kaolin application and two cultivars, Constantí and Vairo. More negative water
potential values were observed in the RDI treatments compared to the FI treatments. There were no
significant differences in the stomatal conductance, photosynthetic rate, or transpiration rate between
treatments with RDI and FI, demonstrating the almond tree’s good adaptation to irrigation reduction
in the kernel-filling stage. The two cultivars had different responses in cumulative yield throughout
the three years of the trial. The cv. Constantí did not present significant differences between the FI
and RDI treatments, translating into improved WUE. In contrast, the cv. Vairo suffered a reduction
in accumulated performance in the RDI treatments with respect to the FI. The foliar application of
kaolin did not present differences in yield and very few in the physiological activity of the almond
trees. With the results obtained, we can suggest that under the conditions of our experiment, the
combination of RDI and the kaolin foliar application can help save irrigation water and produce
almonds more sustainably.
The authors acknowledge the financial support of Operational Group EGIS—Estratégias
de Gestão Integrada do Solo e da Água em Espécies Produtoras de Frutos Secos, PDR2020-1.0.1-
FEADER-030981, funded by PT2020 and EAFRD (European Agricultural Fund for Rural Development).
David Barreales thanks the Foundation for Science and Technology (FCT) for the Ph.D. grants
SFRH/BD/139393/2018 and COVID/BD/152770/2023. This manuscript is part of David Barreales’s
Ph.D. thesis. The authors are grateful to the Foundation for Science and Technology (FCT, Portugal)
for financial support by national funds FCT/MCTES(PIDDAC) and CIMO (UIDB/00690/2020 and
UIDP/00690/2020), and to the Associate Laboratory SusTEC (LA/P/0007/2021).
