Abstract
Aerodynamic and canopy resistances have long been considered to be of key interest in model equation parameterization, particularly for the accurate estimation of crop evapotranspiration. However, model parameters applied in greenhouses showed variation affected by the micrometeorological environment. Three experiments were carried out in a plastic greenhouse to evaluate microclimate effects on resistances of a soilless cucumber crop. The regression analysis of canopy-to-air temperature (Tc − Ta) difference on air vapor pressure deficit (VPD) was substituted into the energy balance equation for the estimation of aerodynamic and canopy resistance values. As expected, a fan and pad evaporative cooling system proved to be the more efficient method of decreasing crop temperature (Tc) compared to the forced air ventilation system. The estimated transpiration by the Penman–Monteith model based on calculated aerodynamic and canopy resistance values successfully validated values measured with lysimeters in different growing periods. In this article, we report for the first time the calculation of aerodynamic and canopy resistance values inside a greenhouse based on equations for an open field that were found in the literature. Results may be helpful in Mediterranean greenhouses for direct determinations of plant water evaporative demand and smart climate control systems.
Highlights
Transpiration is an important component of canopy energy and water balance that should be considered, especially for plastic greenhouses in semi-arid regions
Greenhouse air temperature and vapor pressure deficit values were significantly higher in the forced air ventilation climatic treatment (FV and W-FV ) as opposed to the fan and pad evaporative system (F-PE )
This study shows that fan and pad evaporative cooling was the most efficient system to decrease the vapor pressure deficit (VPD) and the greenhouse air and leaf temperatures
Summary
Transpiration is an important component of canopy energy and water balance that should be considered, especially for plastic greenhouses in semi-arid regions. Under these conditions, transpiration depends mainly on convection rather than decoupling from the outside atmosphere by the presence of the glass [1]. Understanding the transpiration process with a focus on the coupling between the greenhouse microclimate and crop is helpful for adopting proper irrigation and climate control management [2,3]. Kimura et al [4] have demonstrated that the spatiotemporal distribution of leaf boundary layer conductance within a tomato crop canopy may be a useful tool for appropriate microclimate assessment in the greenhouse. The model treated the crop canopy as a Agronomy 2020, 10, 1985; doi:10.3390/agronomy10121985 www.mdpi.com/journal/agronomy
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