The effect of physical properties of soilless media on plant performance - A review

Moderate matric potential and oxygen deficiency reduce leaf water potential, net assimilation rate and transpiration and thus negatively affect plant productivity. Moderate matric potential in the porous media, usually accompanied by a sharp decrease in unsaturated hydraulic conductivity, leads to localized zones of very low matric potential adjacent to the root-medium interface. This phenomenon cannot be easily characterized using tensiometers and is the main limiting factor to water uptake by plant roots. Restricted water uptake results in low leaf water potential, leading to cessation of leaf and shoot expansive growth. Oxygen deficiency restricts root respiration, thus negatively affects water and nutrient uptake. If it persists, temperal loss of ion selectivity of the root membranes may occur, resulting in increased uptake of non-essential ions such as sodium. Water and oxygen status of the root zone can be manipulated at two stages. Firstly, they are 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. The main physical properties of the medium that affect plant performance are discussed in the following review, as well as methods to affect the actual status of water and oxygen in the medium. Abbreviations: ET, evapotranspiration; NAR, net assimilation rate; NCER, net carbon exchange rate; ODR, oxygen diffusion rate; PPFD, photosynthetic photon flux density; WUE, water use efficiency.