Pore Tortuosity and Wettability as Main Characteristics of the Evolution of Hydraulic Properties of Organic Growing Media during Cultivation

Abstract

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).

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

“…This can likely lead to changes in these physical properties, and then in water, air and nutrient availability for plant, with a risk to lead to a poor fertigation management, and then decreases in plant yield and/or quality, or more irremediable crop failures. Kerloch and Michel (2015), in their last paper, reported and confirmed previous works showing these changes in physical properties during time, with contradictory effects observed according to particle size distributions of the growing media. All authors mentioned decreases in air-filled porosity and pore tortuosity because of root growth in the macroporosity progressively filled by them (Allaire-Leung et al, 1999;Nkongolo and Caron, 2006;Caron et al, 2010;Cannavo and Michel, 2013;Kerloch and Michel, 2015).…”

“…Kerloch and Michel (2015), in their last paper, reported and confirmed previous works showing these changes in physical properties during time, with contradictory effects observed according to particle size distributions of the growing media. All authors mentioned decreases in air-filled porosity and pore tortuosity because of root growth in the macroporosity progressively filled by them (Allaire-Leung et al, 1999;Nkongolo and Caron, 2006;Caron et al, 2010;Cannavo and Michel, 2013;Kerloch and Michel, 2015). However, Caron et al (2010) and Cannavo and Michel (2013) showed the decrease in the resulting relative gas diffusivity for fine growing media, whereas Allaire-Leung et al (1999), Cannavo and Michel (2013), and Kerloch and Michel (2015) reported its increase for coarser materials used in their trials (peat, pine bark, coco, and wood fiber).…”

“…and Michel, 2015). Opposite evolutions were also observed for hydraulic conductivity, sometimes with a decrease, respectively for peat, wood and coir growing media (Cannavo et al, 2011;Gruda and Schnitzler 2004;Kerloch and Michel, 2015), sometimes without change for peat-based mixes (Allaire-Leung et al, 1999;Nkongolo and Caron, 2006), and sometimes with an increase for peat, pine bark and wood fiber (Kerloch and Michel, 2015), but all these changes in hydraulic conductivity are always low, not exceeding one order of magnitude in all cases.…”

“…All authors mentioned decreases in air-filled porosity and pore tortuosity because of root growth in the macroporosity progressively filled by them (Allaire-Leung et al, 1999;Nkongolo and Caron, 2006;Caron et al, 2010;Cannavo and Michel, 2013;Kerloch and Michel, 2015). However, Caron et al (2010) and Cannavo and Michel (2013) showed the decrease in the resulting relative gas diffusivity for fine growing media, whereas Allaire-Leung et al (1999), Cannavo and Michel (2013), and Kerloch and Michel (2015) reported its increase for coarser materials used in their trials (peat, pine bark, coco, and wood fiber). Also, Allaire-Leung et al (1999) and Kerloch and Michel (2015) reported increases in water retention at −1 kPa for fine peat based growing media, whereas coarser materials like pine bark, wood fiber and coir did not show any significant change (Kerloch http://dx.doi.org/10.1016/j.scienta.2017.01.023 0304-4238/© 2017 Elsevier B.V. All rights reserved.…”

Organic Materials Used in Agriculture, Horticulture, Reconstructed Soils, and Filtering Applications

“…In containerized soilless crop production, the volume of roots can become as important as the volume of the solid phase in the substrate, and it is easy to understand that during plant growth, fluid transfers properties are deeply modified. Kerloch and Michel (2015) studied the combined effects of root development and irrigation management on the hydraulic properties of sphagnum peat, coir, wood fiber, and bark. The authors found that aeration increased with time as a result of decreased pore tortuosity with increasing effective gas diffusion in all media.…”