Physical characterization of greenhouse substrates for automated irrigation management

Over the last decade, the greenhouse industry experienced a significant increase in production capacity in response to enhanced demand of high-quality crops. To optimize yield and quality of greenhouse crops, substrates with optimal balance of aeration and water holding properties are essential. A wide variety of root zone media such as perlite, rockwool, coco coir, foamed glass or mixtures of these substrates have been successfully used in greenhouse agriculture. There is mounting empirical evidence that dual porosity (i.e., aggregated) media that contain small intra-aggregate pores for water storage and larger inter-aggregate pores for aeration create an improved rhizosphere environment for many crops. To investigate the suitability of these substrates and various mixtures thereof for cultivation of tomatoes, we conducted a comprehensive measurement campaign to characterize water retention properties. The measured substrate water retention curves exhibit various unimodal (e.g., coco coir and rockwool) and bimodal shapes (e.g., foamed class and perlite) with differing air entry potentials, providing valuable information for irrigation scheduling to balance water storage and aeration for optimum growth conditions. Furthermore, the obtained curves can be used to parameterize numerical simulation models for optimization of irrigation strategies and other controllable environmental variables.