Abstract

The optimal water interval based on volumetric moisture thresholds in the substrate (θ_vs), allows precise control of the volume and frequency of irrigation. The research determined the thresholds of θ_vs for irrigation management in tomato and sweet pepper crops in coconut fiber in the greenhouses at the Fabio Baudrit Moreno Agricultural Research Station (EEAFBM), Alajuela, Costa Rica, 2015. In both crops, there were 2 treatments: with irrigation (CR) and without irrigation (SR), in a completely random design. The content of water θ_vs, the water potential (ψ_h) and the leaf temperature (T_h) were evaluated and the evapotranspiration of both crops was estimated by means of a water balance in the substrate. The θ_vs threshold for water management in coconut fiber and both crops could be established in the readily available water range of 56% to 38%, where the ψ_h values were below the critical threshold of < -1 MPa reported by different authors and the T_h were similar to the air temperature. The averages of θ_vs in tomato (44%) and sweet pepper (50%) in CR treatments were within the range of readily available water (38% to 56%) of the coconut fiber. In the SR treatments of both crops, the θ_vs decreased to an average value of 32%, close to the permanent wilting point. The differences between treatments of the ψ_h and T_h were of higher magnitude at midday of 2^nd day. The ψ_h in CR treatments were -0.84 MPa and -0.98 MPa, meanwhile in SR treatments they were -1.24 MPa and -1.3 MPa, in tomato and sweet pepper respectively. At midday of 2^nd day, the T_h of both crops and treatments were similar and lower, respectively, to the air temperature (32.9°C).

Keywords: Irrigation management; water potential; substrate moisture; optimal water content interval; refill point