Effect of Water Content on the Hydration Efficiency of Several Organic Substrates

Hydrophobicity of organic matter is the primary factor affecting soil physical properties after drying. In horticultural productions, the measurement of wettability is even more relevant due to the large use and the high content of organic materials in growing media, and to the large and rapid variations of water content in the media (due to the limited volumes of pot/container). Both of which can quickly create hydrophobic conditions, leading to retardation or resistance of water infiltration and creation of preferential flow paths for water and solutes and then deteriorate physical properties of growing media and plant water uptake as well. In order to avoid these negative impacts for plant growth, and then to improve irrigation management, this work aimed to estimate the hydration efficiency of some traditional and alternative organic materials used as substrates (peat, coconut coir, aged pine bark, wood fiber) under different initial moisture contents: 25%, 37.5%, 50% and 62.5% (by weight). Results showed that hydration efficiency was influenced by initial moisture contents in all materials. Different minimum moisture content thresholds according to the substrates to overcome risks of hydrophobicity could be defined. Thus, coir, bark and wood fiber had a high ability to rewet (hydrophilic products) in contrast with peat which remained hydrophobic for 50% moisture content, and below.