No abstract

From the reviewed literature, it is observed that scientist’s worked on the various substrate medias used for hydroponic system. They also studied about different combinations of the media and their effect on crop growth. The reviewed literature shows that scientists have studied different organic and inorganic media viz. cocopit, saw dust, rice husk vermiculite, perlite, hydroton, pumice, sand etc. It was also found that these media are not easily, cheaply and locally available for users. Beside this, few scientists studied about physical and chemical properties of media such as particle size, porosity, bulk density, wettability, water holding capacity (WHC), Air filled porosity (AFP), Electrical conductivity, pH of these media. The crop specific suitability of combinations of the different media mixtures were also tested and reported by many scientists. It was revealed from reviewed literature that salinity of media caused linear reduction in the water consumption. The size and shape of particle size distribution are useful for estimating the hydraulic properties of the media The substrate under long cultivation period causes increase of organic matter content and microorganism activity which leads to an increased competition for oxygen in the root environment. The optimal EC levels range from 1.5 to 4.0 dSm-1 according to crop and its sensitivity to different salinity levels. It was also observed that level of growing medium temperature close to that of the surrounding air seems more suitable. The ideal substrate should have a total porosity of over 85 percent. Particles of smaller-sized individual grains have a larger specific surface area.