Substrate re-use affects yield and quality of seven radish cultivars grown in a closed soilless system

Seven radish cultivars were evaluated in March-April 1998 using a closed soilless system for the purpose of determining yield in subirrigation with new and re-used substrate. Plants were transplanted in pots (576 cm(3)) containing peat, vermiculite, and perlite in a ratio 1:2:2 (v:v:v). This substrate was either freshly prepared or already used in one or two previous cycles for the same species. Fresh and dry weight of leaves and fresh and dry weight, sponginess and colour of the hypocotyl were measured. Primary inorganic anion content was determined on hypocotyls grown on the substrate freshly prepared. At the end of the cycle, pH and EC of the water extract from the substrate were determined. As the substrate was used more than once and up to three times, dry weight and dry matter content of the hypocotyl decreased linearly (from 7.9 to 5.6 g and from 42 to 34 g/kg of fresh weight, respectively) together with leaf dry weight (from 4.2 to 3.4 g). This was probably due to the simultaneous increase of EC in the water extract of the substrate (from 359 to 502 muS/cm). At the same time, leaf dry matter increased from 69 to 74 g/kg of fresh weight, and the colour of the hypocotyl was less saturated with the red index being lower and less bright. The white round cultivar had a hypocotyl fresh weight lower than red cultivars (2.8 vs. 7.6 g). Among the red cultivars, 'Saxa 2' yielded more than 'Saxa', and 'Champion' more than 'Cherry belle'. The 'White round' hypocotyl cultivar was not spongy, different from cultivars with a red hypocotyl with white tip, which had higher sponginess ratings. Nitrate content was on average 1,305 mg/kg of fresh weight, which is a value rather low compared to those reported in the literature.