Irrigation in soilless culture is generally managed by taking into account the air-illed porosity and water availability of the growing medium for plants, which are determined before culture from the water retention curve. However, many factors can affect the physical properties during the growth period and then lead to poor irrigation. This study aimed to analyze the combined effects of root development and irrigation management on the hydraulic properties of organic media and their consequences for water and air availability for the root system with time. A culture of Radrazz Rosa ´hybrida was performed with four different materials (peat, pine bark, coir, and wood iber) during 6 mo in a greenhouse, with the most common irrigation management between −1 and −10 kPa. Root volume, total volume, air and water retention properties, saturated hydraulic conductivity, relative gas diffusivity, and wettability of each growing medium were measured at the beginning and the end of the experiment. The study showed different physical behaviors for the growing media in terms of air and water retention but mainly highlighted decreases in total volume, pore tortuosity, and wettability and an increase in gas diffusion as the common and most relevant parameters inluencing their evolution with time.Abbreviations: AFP, air-illed porosity; EAW, easily available water.Investments in the horticultural industry (greenhouse, growing media, fertilizer, recycling system, heating, etc.) are generally expensive, and crop failures can lead to severe inancial losses for growers. he main reason for such failure, as noted by experts and producers, is faulty irrigation management of the growing medium, which can lead to ʶ root asphyxia, nutrient leaching (and then pollution), and risks for plant health with the development of pathogens due to excessive irrigation ʶ poor rewetting of the growing medium (with risks of hydrophobicity) and plant physiological stress (nutrient deiciency) under the driest conditions and then a deterioration of plant yield and quality. Knowing these risks, producers generally use coarse growing media with excessive fertigation to avoid water and nutrient stress for the plant (Raviv and Lieth, 2008).

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.

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