Water availability to rose roots grown in soilless media, as a determinant factor of productivity

Low matric potential in porous media is usually accompanied by very low unsaturated hydraulic conductivity (K). This characteristic is the main rate-limiting factor to water uptake by plant roots. Restricted water availability reduces leaf water potential, which, in turn, causes cessation of leaf and shoot expansive growth. Reduced leaf area leads to lower plant productivity. Net assimilation and transpiration rates are also negatively affected by low K, although less dramatically. Water status of the root zone can be manipulated at two stages. Firstly, it is affected by the choice of the medium, in respect to the crop needs, available management practices and climatic conditions, and secondly by the chosen strategy of irrigation control. Maintaining K at a level that is compatible with atmospheric water demand requires, in addition to adequate climatic sensors, real-time measurement of the water status in the medium. Based on our experience this is best achieved by weighing lysimeters and online calculation of water uptake rate while tensiometers, TDR and FD sensors may all yield erroneous results.