EFFECT OF BIOSTIMULATORS ON GROWTH OF VEGETABLES IN HYDROPONICAL SYSTEMS

Biostimulators could be used to stabilize hydroponical systems and to counteract stress situations. The experiment aimed to investigate the effect of lactic acid (LACTOFOL O), K-Humate and Bacillus subtilis as biostimulators in substrate culture of Cucumis sativus cv. Jessica. All substances were applied separately or in combination on leaves and roots respectively, in total 8 different treatments have been compared with the control. For each treatment 20 ml of 0.08% LACTOFOL O, 0.2% K-Humate or 10 cfu/ml spore suspension of Bacillus subtilis were applied three times in weekly intervals during the 5 till 10 leaf stage. Biomass of shoots and leaves was enhanced due to the application of these substances. Also the dry matter content was higher in treated plants than in the control. After application of each biostimulator investigated to the roots the number of marketable cucumbers was enhanced in total and in relation to the non-marketable fruits. The application of K-Humate enhanced also the dry matter content of the cucumbers. The application in the root zone had a stronger effect than the application on the leaves and should be preferred. The combined application of all substances was possible but should be investigated further. INTRODUCTION Since about 15 years, also substances with biological origin have been used to avoid or counteract abiotic or biotic stress in horticulture. In hydroponics, investigations about effect of such biostimulators are scares until now. In previous investigations we found beneficial effects in hydroponics of the gramnegative rhizobacterium Bacillus subtilis FZB 24® regarding the reduction of salt stress (Boehme, 1999) and its effects against fungal and bacterial diseases are also proved (Loeffler et al., 1968; Krebs et al., 1998; Schmiedeknecht et al., 1998; Grosch et al., 1999). Beside microorganisms, also organic substances with different chemical composition can be used as biostimulators, e.g. humates and lactates. Also for these substances growth stimulating and stress-reducing effects could be shown in hydroponics (Boehme, 1999; Boehme et al.; 2000, Hoang, 2003). Humates well know, as main components of soil fertility have so far more or less no importance in hydroponics. However, some very interesting effects of humates are described concerning their stimulating effect on nutrient uptake (Fortun and Lopez, 1982; Tattini et al., 1989), counteracting salt and drought stress as well as temperature stress. The positive effect of humates on availability and uptake of nutrients like calcium, magnesium, and phosphorus due to chelating should be stressed. Lactates, salts of lactic acid, can be also used to chelate nutrients, especially micronutrients. Stress reducing effects of lactates could be found especially in nutrient solutions with too low or too high pH values and also in stress situations because of extreme temperature (Boehme et al., 2000). Several products of a Bulgarian company ECOFOL are offered as foliar fertilizer with the brand name LACTOFOL. All substances described have beneficial effects on plants in stress situations, however, their main effects they have in different stresses. Therefore, a combination of these substances should be investigated to stabilize the growing conditions. The experiment presented here was done with cucumber a very sensitive plant even under standard conditions. It should be find out if such combination of these substances supports their beneficial effects or if they interfere with each other. The biostimulators can be applied in the root zone or on the leaves. It should be investigated which treatment is the most effective one. Proc. IS on Soilless Cult. and Hydroponics Ed: M. Urrestarazu Gavilan Acta Hort. 697 ISHS 2005 338 MATERIAL AND METHODS Plant Material and Growing Conditions Plants of Cucumis sativus L. cv. Jessica were used for the experiment. Cucumber seeds of cultivar Jessica were sown on 15-th of May 2003. Planting was conducted on 10-th of June. For the investigation in large scale in greenhouse, cucumber plants were grown in substrate culture using containers with perlite. Perlite with an average dry density of 120 kg * m3 was used. The grain size was between 0.06mm and 1.5mm, with 45% of all grains having been 1mm in diameter. Pore volume was 84% v/v, the water holding capacity was 45% v/v, and the air capacity was 39%. Nutrient solution was calculated with the HYDROFER computer program to adjust the amounts of fertilisers, salts and acids required (Boehme, 1993) according the values (170 ppm N, 50 ppm P, 260 ppm K, 150 ppm Ca, 60 ppm Mg, 3 ppm Fe, 90 ppm HCO3, 80 ppm S). By trickle irrigation 2 to 4 times a day 250ml per irrigation cycle was applied in period of 12-15 min. Current experiment covers the period from 15-th of May through beginning of August 2003. Average temperature during the day was equal to 27.5°C and during the night 23.5°C. Experimental Design Eight different treatments were compared with the control (Table 1). K-Humate (Fa. Humintech), Lactofol (O) (Fa. ECOFOL, Table 2) and Bacillus subtilis FZB 24 (Fa. FZB) was applied on leaves or in the nutrient solution. Quantity and concentration of applied substances were deduces from either previous experience (Bohme, 1999) or by using application instructions of manufacturer (Bacillus subtilis FZB 24). Timing of application coincided with transplanting of seedlings into big vegetation pots (Mitscherlich Pots with volume of 8 litres). Plants were treated three times in weekly intervals in following development stages: first treatment 5-6 leaves stage; second: 7-8 leaves stage; third: 9-10 leaves stage. Quantity of substances applied is 20 ml per pot and plant. Leaf application was conducted through spraying of the solution of given substances on surface of the leaves. Watering in substrate was conducted through direct application of solutions into the root area of the plants. Data Collection In the course of the experiment plant height, number of leaves, leaf area as well as EC value, pH value and nitrate content of the substrate were recorded weekly. The pH in the control dropped down from 6.8 to 5.3. All treatments started with same pH, but after the experiment the pH values had more or less the same value as in the beginning. The initial EC values ranged from 1.3 till 1.9. In the control and in the leaf treatments the EC raised to 3.7. The variant with root treatment, however, had EC values between 1.9 and 2.8. Harvest of cucumbers started on the first of July and finished on the fourth of August. For evaluation the yield of 9 days were pooled. The quality of cucumbers was evaluated concerning number of marketable and non-marketable fruits, weight, length, and diameter of each fruit. After finishing the experiment three plants of each treatment were evaluated concerning fresh and dry matter of shoots and leaves. Statistics The experiment comprised 9 plants per treatment (3 x 3 replicates) randomized distributed. Data were evaluated by ANOVA (SPSS) and the statistic tests Chi square (Pearson) and LSD. RESULTS AND DISCUSSION A three times application of biostimulators in the growing stage (week 4, 5, and 6) affected growth and yield of cucumber plants. Shoot Development The application of all substances tested stimulated the shoot development represented by a higher fresh matter of shoots and leaves in most variants (Fig. 1a). Obviously the