Evaluation of recycled rockwool as a component of peat-based mixtures for geranium (Pelargonium peltatum L.) production

The chemical characteristics of used rockwool slabs as well as the physical properties of four mixtures of peat and blended rockwool (i.e. from 0 to 60%, rockwool/peat, vol/vol) were determined as a culture medium for geranium production. The production was studied under two values of substrate water potential considered as the initial set points controlling fertigation (-15 and -10.kPa). Results showed that used blended rockwool, when combined with peat, appears to have certain properties which result in an increased air space together with a decrease in volumetric water content. When water potential decreased from 0 to -10.kPa, the blended rockwool lost about 85% of its water content, whereas only 62% of the water content of saturated peat was lost at the same water potential. However, volumetric easily-available water was slightly affected by the incorporation of used rockwool to the peat substrate. Compared with peat, used rockwool showed higher contents of soluble minerals. The mean electrical conductivity values of the extracted solutions reached a maximum of 3.11.mS cm^-1. When fertigation was started at -15.kPa, some parameters such as plant aerial dry weight, leaf area, number of inflorescences per plant, and number of plants with at least one opened flower, decreased concomitantly with an increase in rockwool content. Nevertheless, only those plants grown in a mixture containing the highest volumetric rockwool content (i.e. 60%) resulted in inadequate quality for market. In contrast, when supplying fertigation at -10.kPa, all parameters were similar to those of controls, except for those plants grown in the mixture containing the highest volumetric rockwool content (i.e. 60%), where although a lower biomass production was observed, a similar production of inflorescences per plant and market quality was found. It is concluded that blended recycled rockwool can be used successfully as a component of peat-based media for geranium production as long as the fertigation schedule is modified according to the physical properties of the media.