S06 - Session O1 - Sustained growth and yield in elevated greenhouse air temperatures through control of vapor pressure deficit.

Authors: Gene A. Giacomelli, Joe Alcorn *, Brian Scott

A novel method of utilizing the abundant solar radiation in arid lands to treat brackish water will integrate a humidification/dehumidification (HDH) thermal desalination system into a controlled environment greenhouse producing food crops. The HDH system efficiency increases with higher air temperatures than are considered upper limits of air temperatures for growing food crops. Developing a crop production system that operates at upper threshold air temperatures creates plant physiological challenges. Multiple experiments were performed in which tomato and lettuce crops were grown in optimal conditions of 24 °C photoperiod air temperature, and then at upper threshold air temperatures of 30 °C, both with and without supplemental air moisture to lower the vapor pressure deficit (VPD). Maintaining an optimum VPD with a low-pressure mist system was intended to mitigate excessive plant transpiration and promote sustained plant growth during the elevated photoperiod air temperatures. Plant measurements for growth and development exhibited marked declines without VPD control of -11.8% Apical growth, -15.0% Mature leaf length, -11% Fruit yield, and -41% Average fruit weight, but maintained improved relative growth and development with VPD control of -6.4% Apical growth, -6.6% Mature leaf length, -0.3% Fruit yield and -0.1% Average fruit weight. Greenhouse environmental conditions that increase the HDH thermal desalination system efficiency can also favor plant growth and development, if VPD is controlled, thereby achieving solar desalinization and crop production simultaneously within the same facility.