Relevant hydraulic properties of peat-based mixes for explaining root development according to irrigation strategies

The effects of irrigation strategies on root development depending on the initial physical and hydraulic properties of peat-based mixes were studied within cultures of Ipomoea batatas 'Margarita' for which watering was managed by: 1) maintaining the water potential at container capacity; 2) triggering the irrigation when water potential reached -32 kPa. Three growing media with respective ratios of 100:0:0:0, 70:10:10:10 and 40:20:20:20 peat:bark:coir:wood fiber by volume, each prepared at two different compression levels, were used in order to have various initial physical and hydraulic properties at the beginning of the experiment. Root volume, pore space, air and water retention properties, saturated hydraulic conductivity, relative gas diffusivity, and wettability were measured at the beginning and then at the end of the experiment. The study showed important changes over time as a result of both irrigation strategies and initial physical and hydraulic properties of the tested growing media. However, relevant parameters explaining root development were depending on the irrigation strategies: results confirmed the importance of water content and its consequence on wettability in case of restrictive irrigation (-32 kPa), whereas air flow seemed to be relevant for predicting root content for non-limiting irrigations (-1 kPa).