In most micropropagation systems minerals and other components of the medium are provided at a certain concentrations at the beginning of culture and depleted later on due to intake by the micro-plants
One out of many references for this is shown in the chart below. (Croak ML. 1972) Accordingly we can state that the plant in culture is subjected to reducing concentrations of nutrients. In view of the increase of plant mass during culture period, the demand for nutrients should rather be growing… In order to address this dilemma a steady release of minerals through the addition of CONTROLLED RELEASED FERTILIZERS (CRF) in the culture medium can be tested. " A controlled-release fertilizer (CRF) is a granulated fertilizer that releases nutrients gradually into the soil (i.e., with a controlled release period)… The fertilizer granules may have an insoluble substrate or a semi-permeable jacket that prevents dissolution while allowing nutrients to flow outward." (Wikipedia). The idea of using CRF in plant tissue culture was described in a patent (Sluis CJ et al 1990 WO1990010691 A1).
