Research paperEvolution of hydraulic properties and wettability of organic growing media during cultivation according to irrigation strategies

- Large changes in physical/hydraulic properties of growing media during cultivation.
- Hydric history has a large role in the evolutions of physical/hydraulic properties.
- Wettability is one of the main relevant parameter explaining these evolutions.
- Lower (vs hydric history) but positive effects of the root system.

Recent studies have shown that growth period largely affected physical properties of growing media, and therefore irrigation management has to be revised according to these changes in order to avoid poor irrigation. Decreases in pore tortuosity but also in wettability have been identified as the most relevant parameters explaining these evolutions with time, as a result of combined effects of root growth and irrigation regimes. So, this study aimed to analyse the respective effects of root development and irrigation strategies on the physical and hydraulic properties of four different growing media (peat, pine bark, coir and wood fiber) within a culture of Rosa × hybrida “Radrazz” grown with and without plants during four months, for which watering was managed in three different ways: (1) water potential always maintained at −1 kPa, (2) irrigation triggered when water potential reached −10 kPa or (3) −30 kPa.Root volume, total volume, air and water retention properties, hydraulic conductivity, relative gas diffusivity, and wettability were evaluated at the beginning and at the end of the experiment. The study showed important changes over time, mainly due to the hydric history, leading to large and higher modifications of pore size distribution, tortuosity and wettability as a function of the intensity of the drying/wetting cycles. Changes in wettability, and notably, more hydrophobic properties of the coarser porosity due to its drainage during the drying processes were suggested for explaining the general physical/hydraulic behaviour of growing media, and the decrease in shoot dry mass and root content with the intensity of irrigation regimes. Although they were with smaller amplitude to those resulting of the hydric history, positive effects of the root system were shown, increasing pore connectivity, relative gas diffusivity and limiting the decrease in total pore volume, and moreover, limiting the degradation in wettability.