Introduction.

Physical-hydraulic characterization of substrates is critical for designing irrigation strategies aimed at enhancing water and nutrient use efficiency and improving crop performance in greenhouse systems. Objective. To evaluate the effect of three levels of water depletion on the physical-hydraulic and physicochemical properties of the substrate, as well as on growth, yield, and water use efficiency of sweet pepper and tomato crops grown in coconut fiber (coir) under greenhouse conditions. Materials and methods. The study was conducted from August 2020 to January 2021 in a multitunnel greenhouse at the Fabio Baudrit Moreno Agricultural Experiment Station, Alajuela, Costa Rica. Three substrate water depletion levels (Ag11, Ag22 and Ag32) were evaluated in a completely randomized design with three replicates. The response variables included volumetric water content (θ), unsaturated hydraulic conductivity (K(θ)), pH, electrical conductivity (EC), irrigation volume and frequency, leaf area, dry matter, marketable yield, and water use efficiency (WUE). Data were analyzed using the R statistical environment. Results. The Ag11 treatment, characterized by more frequent irrigations with lower volumes, maintained adequate moisture, stable EC, and higher K (θ), which promoted greater vegetative and reproductive growth, as well as high water use efficiency (WUE). The Ag22 treatment achieved yields and WUE values equivalent to those of Ag11, with lower irrigation frequency but higher volume irrigations, without increasing EC to critical levels. The Ag32 treatment significantly reduced growth, yield, and WUE, without raising EC to critical levels, showing a similar irrigation frequency to Ag22 but with a higher applied volume. Conclusions. The Ag11 treatment represented an equilibrium among aeration, water retention, and hydraulic and electrical conductivities, as evidenced by stable yields and efficient water use.