Numerical Simulations of Root Zone Fluid Fluxes in Greenhouse Substrates.

Over the last decade, the greenhouse industry significantly expanded production capacity in response to increasing demand of high-quality crops. Growth substrates with optimal balance of aeration and water holding properties are essential for optimizing quality and yield of greenhouse crops. A wide variety of root zone media such as perlite, rockwool, coco coir, foamed glass, or mixtures thereof have been successfully used in greenhouse agriculture. Empirical evidence suggests that dual porosity media that contain small intra-aggregate pores for water storage and larger inter-aggregate pores for aeration create an improved rhizosphere environment for many greenhouse crops. To investigate the suitability of these substrates for greenhouse agriculture, we conducted a comprehensive measurement campaign to characterize water retention and other physical properties. The measured substrate water retention curves exhibit various unimodal and bimodal shapes with differing air entry potentials, providing valuable information for irrigation scheduling to balance water storage and aeration for optimum growth conditions. Obtained properties were used to parameterize a 3-D HYDRUS model to optimize irrigation frequency and discharge rates for a typical growth bag. Simulations compared favorably with laboratory experiments conducted under controlled environmental conditions.