Use of Biostimulants for Reducing Nutrient Solution Concentration in Floating System

The production innovations have been evolving more and more towards organic, sustainable or environmental friendly systems. Contemporarily, the yield and the quality of crops must be assured. The reduction of fertilisers may be obtained by improving the nutrients uptake or their utilisation by the plants. The aim of our work was to verify if the progressive reduction of nutrient solution concentration in the floating system can be compensated by applications of a biostimulant (Actiwave®, Valagro S.p.a.) without compromising the yield and the quality of vegetables. The experiments were performed on rocket (Eruca sativa Mill.) grown in floating system with standard nutrient solution (NS100%), which was compared with nutrient solutions diluted 4 (NS25%) or 10-fold (NS10%) with or without 0.3 ml L Actiwave. At harvest, yield, leaf area, root dry weight, chlorophyll, carotenoids, and leaf nitrate content were determined. Results showed that Actiwave significantly increased the nutrient uptake and nutrient use efficiency in all treatments. In fact, no statistically significant differences were found in yield between NS100% and NS25% plus 0.3 ml mL Actiwave. Moreover, Actiwave reduced the leaf nitrate content and increased chlorophyll and carotenoids in all treatments. Our results indicate that Actiwave lowered the leaf nitrate content through its ability in stimulating nutrient uptake and nitrogen metabolism. The combination of hydroponics and biostimulants appears as a promising environmental friendly strategy for the greenhouse production of highquality vegetables. INTRODUCTION The minimally processed or fresh-cut leafy vegetables have been gaining importance in the world-wide vegetables market (Brecht et al., 2004). The consumer demand has been increasing in recent years and many farmers oriented their production plans towards the baby leaf vegetables such as lettuce, spinach, rocket, lamb’s lettuce and Swiss chard. The floating system is an adequate growing system that provides leafy vegetables with higher sanitary quality without soil contaminants. This hydroponics system usually reduces the nutrients and water use with huge benefit for the environment. However the application of biostimulants directly in the nutrient solution may improve the nutrient use efficiency and leafy vegetables quality (Vernieri et al., 2005). Trials performed on rocket showed that biostimulants also increased the chlorophyll content even if the nutrient solution was diluted by 4-fold (Vernieri et al., 2005). Total chlorophyll content affects the colour and the visual appearance of the leafy vegetables, subsequently the attractiveness for consumers (Ferrante et al., 2004). The mechanisms behind the effects of biostimulants are still unknown. The isolation of the substances that compose the biostimulant, is not easy and the result may be due to a synergistic effect of many components such as mineral elements, vitamins, amino acids, etc. (Berlyn and Russo, 1990). Proc. IIIrd IS on HORTIMODEL2006 Eds. L.F.M. Marcelis et al. Acta Hort. 718, ISHS 2006 478 The aim of this work was to investigate how much the standard nutrient solution in combination with a biostimulant can be diluted without affecting the yield and quality of leafy vegetables. MATERIALS AND METHODS Plant Material and Growing System Rocket (Eruca sativa Mill.) was grown in a floating hydroponic system. Seeds were directly sown in trays containing perlite. After emergence (about 10 days after sowing) all the trays containing seedlings were placed in floating tanks containing nutrient solution. The electric conductivity (EC) was 1.9-2.2 and pH was adjusted to 6.06.5. The cultivation was performed under a glasshouse located in Pisa. Treatments with Biostimulants Rocket plants were grown in floating systems with the following nutrient solution (concentrations are expressed in mM): 1) standard, i.e.: undiluted solution (NS100%) 12 N-NO3, 3.8 N-NH4, 2.8 P, 8.4 K, 3.5 Ca, 1.4 Mg, 9.5 Na, 8.0 Cl, 2.7 S, 0.04 Fe and Hoagland’s concentration for micronutrients with or without 0.3 ml L biostimulant (Actiwave). 2) 4-fold diluted solution (NS25%) with or without 0.3 ml L Actiwave. 3) 10-fold diluted nutrient solution (NS10%) with or without 0.3 ml L Actiwave. Sampling and Measurements At the harvest time, yield, leaf chlorophyll, and nitrate content were measured. Chlorophylls and carotenoids were extracted using methanol 99.9% as solvent. Samples were kept in dark cold room at 4°C for 24 hours. Leaf pigments determination were immediately carried out after extraction. Absorbance readings were measured at 665.2, 652.4 and 470 nm. Total chlorophyll and carotenoids were calculated by Lichtenthaler’s formula (1987). Nitrate content was measured by the salicylic-sulphuric acid methods. Each sample (100 mg of DW) was ground and placed in 30 ml icon glass with 10 ml of distilled water. Samples were extracted for 2 h at room temperature, under continuous shaking, then centrifuged at 4,000 rpm for 15 min. The supernatant was recovered and 200 μl were added to 800 μl of 5% salicylic acid in sulphonic acid. The mixture was placed on a stirrer and 30 ml NaOH 1.5 M as slowly added. Samples were cooled to room temperature and spectrophotometer readings were performed at 410 nm (Cataldo et al., 1975). The nitrate content was calculated using calibration standards containing 0, 1, 2.5, 5, 7.5 and 10 mM KNO3. Statistical Analysis Experimental design was composed by 3 blocks completely randomised and each block included six treatments (3 nutrient solution concentrations and 2 biostimulant concentrations). The data were subjected to two-ways analysis of variance and the differences among treatments were analyzed by Bonferroni post-test (P<0.05). The data are reported in figures and table as means ± standard errors. Each treatment was composed by 3 replicate tanks. RESULTS Rocket plants were grown in a floating system with standard nutrient solution and diluted by 4 or 10-fold with or without the biostimulant. The quality and yield of leafy vegetables produced were evaluated at the harvest time. The yield was higher in treatments with Actiwave at lower nutrient concentration, NS 10%. (Fig. 1). The leaf nitrate content was lowered by Actiwave in the treatment with NS25%, while no differences were recorded in the other treatments (Fig. 2). Leaf area, analogously as observed for the yield, was higher in rocket plants