Gas Diffusivity-Based Analysis of Tomato Growth Media.

Growing plants in containerized media has long been a common horticultural practice in the world. Compared to the plants grown in uncontrolled environments, container-grown plants have restricted access to key plant needs such as air, water and nutrients. The properties of growth media play an important role in this regard, and hence appropriate selection of growth media will be the key for successful plant growth. Among different materials tested, coarse-textured media have proved to be well-suited for optimal plant growth. In this study, we examined soil-gas diffusivity, Dp/Do (Dp and Do are gas diffusion coefficients in soil-air and free air, respectively), of five coarse-textured media (perlite, foam glass and a mixture thereof, GrowWorld fine and GrowWorld coarse) and also two fiber-based materials (rockwool and coconut coir), which are to be considered as future tomato growth media. A mixture of foam glass and coconut coir was also tested. The aeration fingerprints for the media were obtained using the Dp measurements carried out on 100-cm3 samples from wet to complete dry conditions following stepwise air drying. The ‘oxygen diffusivity windows’ for the media were also examined in search of the optimal oxygen diffusivity window for tomato growth. A linear relation between mean particle size and percolation threshold observed in a previous study was successfully used to estimate the percolation threshold for gas diffusivity in each medium. A recently developed inactive pore density-corrected (IPDC) model could well describe the gas diffusivities observed for most of the selected media and an extended two-region IPDC model was introduced for the media with significantly large intra-aggregate percolation threshold values. In perspective, the observed oxygen diffusivity windows, together with the measured soil-water characteristics, will be useful for the optimal design of growth media in earth-based and future space-based applications.