FLOATING SYSTEM CULTIVATION OF RADISH (RAPHANUS SATIVUS L.): PRODUCTION AND QUALITY

The floating system is an interesting culture system on a liquid media that can be applied to produce fresh vegetables ready to eat, that are more appreciated by the consumers. The aim of this study was the optimization of the red type radish production on float system in order to obtain a high quality fresh product. Two growing cycles (from May 19 to June 8 and from June 11 to July 1, 2004) were carried out to investigate the effects of two cultivars (Girox and Suprella), and two plant density, (720 and 1368 plant/m) on yield and radish quality. Treatments were arranged in a randomized complete block design with four replicates. Yield, as number of plant/m, fresh and dry weight of leaves and hypocotyls, mineral content and antioxidant activity of leaves and hypocotyls were measured. The 720 plants/m investments give the highest yield a valid agronomic result immediately practicable and allow a higher investment in comparison with conventional system on soil (~300 plants/m). The obtained product was suitable for radish as ready to eat product and had an high quality as regard to its antioxidant activity. The results demonstrated that the grower may improve yield and fruit quality of radish by switching from soil to floating system cultivation. INTRODUCTION In the last years, radish (Raphanus sativus L.) has become an important commercial crop in Italy especially in Lazio region where each year are grown about 43 ha (www.istat.it). The increasing of radish cultivation has been generated by an increasing request of this fresh product on national and European market, especially in the northern European Countries like Holland and Germany. The qualitative characteristics of radish like colour, bright, form and sponginess of hypocotyls are related to genotype and agronomic practices (Park and Fritz, 1984). Several studies showed that plant density and time of sowing (Kanwar, 1993), nutritional and water management (Park. and Fritz, 1984; Weston and Barth, 1997; Beverly et al.1993; Capeka and Libik, 1998) can affect significantly the yield and quality of radish. An important quality characteristic of radish which needs to be optimized is the total antioxidant activity due to molecules with scavenging radicals oxygen activity. The protective role of these molecules in the prevention of human degenerative diseases has been widely demonstrated by many studies (Basu, 1999; Ghiselli et al., 1997; Meyer et al.,. 1997; Tijburg et al. 1997). The importance of radish as source of antioxidant is due to its content of acid ascorbic and phenol, mainly phenolic acids (TaKaya et al., 2003; Sgherri et al., 2003). Float system has shown to be suitable to realize an appreciable yield, especially for leaf vegetables like lettuce, corn salad and spinach. These vegetable crops are widely used for production of fresh vegetable ready to eat or ready to be cooked (Nicola et al., 2002). The aim of the current study, was to assess the effect of two cultivars and two plant densities in terms of yield, mineral composition and quality of radish hypocotyls produced in floating system. Proc. IS on Soilless Cult. and Hydroponics Ed: M. Urrestarazu Gavilan Acta Hort. 697 ISHS 2005 88 MATERIALS AND METHODS Growing Condition and Plant Material The research was carried out at the experimental farm of University of Tuscia (Central Italy) in an unheated greenhouse on a floating system. A randomized complete block design with four replicates was used to compare a factorial combination of two plant density (720 and 1368 plants/m) and two cultivars (Girox and Suprella  seed company Vilmorin, Nunhems). The growing system was constituted by polystyrene panels floating in polystyrene tanks filled to a depth of 20 cm with 20 l of nutrient solution A perlite and vermiculite media (9:1 v/v) and a standard solution were adopted. The nutrient solution had the following composition (ppm): Ca(NO3)2 (903), KH2PO4 (205), K2SO4 (274), Mg(NO3)2 (384), NH4NO3 (40), FeEDTA (30) and microelements mix 0,1ml/l. The experiment was repeated during two consecutive growing cycles starting from 19 May to 8 June 2004 and from 11 June to 1 July 2004 (20 and 21 days, respectively). The average air and nutrient solution temperatures were of 25°C and 22°C, respectively, during the first growing cycle, and 30°C and 25°C respectively, during the second cycle. The seeds were sowed into substrate at superficial depth to permit the regular germination process. During germination period the liquid media was constituted only by water that was replaced, after three days with the nutrient solution. During both growing cycles the pH, EC and dissolved O2 values were monitored weekly. The EC values ranged between 0.9 and 1.9 dS/m, the pH ranged between 5.5 and 6.5. Finally, oxygen concentration was about 65%. Fresh nutrient solution was periodically added to balance the losses related to transpiration rate and elemental uptake by radish plants. The added volume was utilized to calculate water requirement. Nutrient solution samples were collected three times during each growing cycle and analyzed by Inductively coupled plasma spectrometric analysis. The number of germinated seeds and plant surviving were recorded and expressed as % germination and % survival, respectively. At the end of both growing cycles, the number of plant/m, fresh and dry weight of leaves and hypocotyls, size of hypocotyls and distribution of size classes, together with analysis of the edible product were recorded. Macro and micro elemental content in leaves and hypocotyls were determined by the dry ashing method at 400°C for 24 hours ; then the ash were dissolved in 25ml HCl solution 1:25. The obtained plant tissue ash solution was analyzed by ICP spectrometric analysis. The hypocotyls and leaves N content, was determined after mineralization with sulfuric acid by Regular Kjeldahl method (Bremner, 1965). Antioxidant activity of leaves and hypocotyls was determined as DPPH (α,α diphenilβpicrylhydrazyl) radical scavenging activity according to the method of Hatano et al. (1988). All results were analyzed by ANOVA method. Differences between average values was evaluated by Multiple Range and LSD tests with P value <0.05, using the StatGraphic Plus Package (2000). RESULTS AND DISCUSSION The addition of fresh nutrient solution allowed to maintain the nutrient composition at a constant level and to balance the losses due to the transpiration rate and to the element uptake. Differences in water requirements were observed between two investments for each growing cycle. The water consumption was increased of approximately one and half on JuneJuly period (Table 1). These result are probably due to the climate conditions (e.g. solar radiation and VPD) and solution temperatures. Yield At the end of the cultural cycle the fresh and dry weight of hypocotyls and leaves were determined. The results showed that for both growing cycles a dry matter of 4 and 6 % for the hypocotyls and the leaves, respectively without differences between the two examined cultivars nor between two growing cycles (data not reported). The total number of harvested hypocotyls/m at 720 and 1368 plants/m were 489 and 699, respectively while the unmarketable numbers were 81 and 255 respectively (Table 2). Its important to underline that 81 and 255 hypocotyls were unmarketable due to their small size and not because they were cracked. Moreover the unmarketable hypocotyls were in the central portion of the panel which lead to a competition for light among plants resulting in