Physiological and agronomic response of young ‘Verna’ lemon trees to the application of partial root irrigation compared to conventional deficit irrigation under conditions of high evaporative demand

The cultivation of lemon fruits for the fresh market in Spain is located mainly in the southeastern region of the country, an area characterized by a high evaporative demand and the scarcity of rainfall, chiefly during the summer. Under these conditions, it is common to suffer scarcity of water resources, which forces lemon growers to apply irrigation doses that are below the water requirements of the crop. An alternative to optimize the use of available water is the application of deficit-irrigation strategies, such as regulated deficit irrigation (RDI) and partial rootzone drying (PRD). Many studies were conducted on mature trees, but there is little information regarding the use of RDI and PRD in young lemon trees. Thus, this study was carried out to compare the effects of RDI and PRD during a period of high evaporative demand on plant physiological response, yield, and fruit quality of 2-year-old ‘Verna’ lemon trees during the first years of the plantation (2017-2019) in an experimental orchard located in southeastern Spain (Torre Pacheco, Murcia). Irrigation treatments included: i) full irrigation (control), where 100% of crop evapotranspiration (ETc) was supplied; ii) RDI, and iii) alternate PRD, where the irrigation dose was reduced at 75% ETc during the period comprised between May and mid-August. For the PRD treatment, during this period, the irrigated side was alternated every 28 days. Main results showed a better behaviour with PRD than with RDI. On the one hand, PRD reduced stomatal conductance and vegetative growth compared to fully-irrigated trees due to a change in the distribution of resources. On the other hand, PRD trees conserved a similar yield as that of control trees, and it allowed for the maintenance of crop water productivity. Based on these results, under water scarcity conditions, we recommended using PRD in young lemon trees; with this treatment, the entry into production of the crop was less affected.