IRON SUPPLY OF CUCUMBERS IN SUBSTRATE CULTURE WITH HUMATE

The aim of the experiments was to investigate the effect of application of a well soluble Fe-humate (HUMIRON) on rhizosphere and leaves, respectively, on the growth and yield of cucumbers (Cucumis sativus cv. Jessica). HUMIRON type R (extracted from Russian coal) and G (extracted from German coal) were compared. In the first experiment three different concentrations (0.001%, 0.1%, and 0.2%) of HUMIRON were used in three different growing stages of cucumber plants. In the second experiment HUMIRON-G and K-humate were applied to the upper or lower surface of the cucumber leaves. Cucumbers were grown in a substrate culture used containers with 8 l perlite. Nutrient solution with and without iron was applied with trickle irrigation. The results clearly show the application of Fe-humate has beneficial effects on the plant growth and the fruit yield if the nutrient solution had a lack of iron. Iron imbalances or deficiency can be counteracted by application of Fe-humate to the root zone. The additional iron supply did not inhibit the growth and decrease the yield even if the iron supply in the nutrient solution is sufficient. The different effects of the humate types (HUMIRON R and G, K-humate) compared here indicate that the influence of humate can be important. INTRODUCTION Plant cultivation in hydroponical systems is quite problematic concerning the proper balancing of the nutrient supply. According to previous investigations, humates seem to have a particular favourable effect on the nutrient supply. Therefore the application of humates was tested as an approach to improve both the nutrient balance and plant vitality. Humates can stimulate the uptake of macroand microelements. Tattini et al. (1990) and Adani et al. (1998) found that humic acid promotes the uptake of N, P, Fe and Cu of tomato and other plants. The positive effect of humic acid on the uptake of N, P, Fe and Zn was also proved with corn plants (Fortun and Lopez, 1982). Moreover, humates influence the respiration-process, the amount of sugars, amino acids and nitrate accumulated, and make the plants resistant against diseases and viruses. Nevertheless it is very important to stabilize the supply of macroelements; much more essential for plant growth in substrate culture is the sufficient supply with microelements. Often there are disorders of them especially there is iron deficiency. It is assumed that humic acids have special importance for transportation and availability of microelements in the plants (David et al., 1994). Chlorosis could be prevented, by humate application; probably because the availability of iron was enhanced (Fortun and Lopez, 1982; Alvarez et al., 1996; Kreij, de and Hoeven, 1997). So far, NH4-, Kor Ca-humates have been used and positive effects on plant growth could be proved (Hoang, 2003). The background of these effects, however, is not completely clarified. But it can be assumed that the effects are not explicable with the content of nutrient applied together with the humates because their concentration is very low. Now, humates with a high content of metal-ions are available. This amount of metal-ions bound on humate could influence the content of micronutrients in the nutrient solutions directly. The aim of theses experiments was to investigate the effect of application of a well soluble Fe-humate (HUMIRON) on rhizosphere and leaves, respectively on the growth and yield of cucumbers. MATERIALS AND METHODS Plant Material and Growing Conditions Plants of Cucumis sativus L. cultivar Jessica were used for both experiments. For the Proc. IS on Soilless Cult. and Hydroponics Ed: M. Urrestarazu Gavilan Acta Hort. 697 ISHS 2005 330 first experiment cucumber seeds were sown on 7th of October. The plants were transplanted on 28th of October. For the second experiment seeds were sown on 12th of January 2003. Planting was conducted on 28th of January. Cucumbers were grown in a substrate culture with trickle irrigation. The containers were filled with 8 l 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%. The standard nutrient solution (Boehme, 1993) was used with complete macroand micronutrients (170 ppm N, 50 ppm P, 260 ppm K, 150 ppm Ca, 60 ppm Mg, 3 ppm Fe, 90 ppm HCO3, 80 ppm S) and compared with the same nutrient solution but without iron addition. The containers were irrigated with a trickle irrigation system. ‘Netafim’ drippers with a capacity of 2 l hwere used. The plants were irrigated 2 to 4 times a day and 150ml per irrigation cycle was applied in periods of 10-12 min. The salt concentration (EC) in the nutrient solution was between 2.0 and 2.4 mS cm-2, the pH value ranged from 5.8 till 6.5. For the first experiment artificial light was supplied with lamps of type PL-90 E and a radiation power of 120W m2 was used between 7:00 and 19:00h to guarantee 10 Klux. In the second experiment the PAR ranged from 40 to 70 Wm2. Night temperature did not drop below 18°C, day temperature was kept around 22°C and relative humidity was, approximately, 70%. Humate Treatments In the first experiment two types of HUMIRON (Humintech GmbH, Germany) were compared; one type contains humic acid extracted from a Russian coal (R) and the other humic acid from a German coal (G). The humates were applied on the root zone. In the second experiment HUMIRON-Gand K-humate were applied to the upper or lower surface of the cucumber leaves. Per plant 20 ml humate were applied. For root zone treatment three different concentrations (0.001%, 0.1%, and 0.2%) of HUMIRON were used. For leaf application a 0.05% HUMIRON-G and K-humate solution was used. 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. Data Collection and Evaluation For the root zone treatment (first experiment) the plants have been cultivated during the winter time (07-10-2002 till 14-02-2003). Harvesting started in January. The second experiment for leaf application of humates was conducted from January 2003 till April 2003. Harvesting started at 15 of March. Parameters as leaf area and fruit yield were recorded weekly. Harvests for 10 days were pooled and evaluated together. Fresh weight of leaves and shoots were measured in the end of the vegetation. Values of pH and EC in the nutrient were estimated weekly. Statistics The experiment comprised 6 plants per treatment (2 x 3 replicates) randomized distributed. Data were evaluated by ANOVA (SPSS) and the statistic tests Chi square (Pearson) and Tukey-test. RESULTS AND DISCUSSION In the beginning of the experiment the pH of the substrate in all variants treated with HUMIRON was about 7.5. Weekly this value decreased up to a pH of 5.8. Remarkably although the pH dropped no precipitation of the humates could be observed. Vegetative Growth The fresh matter of stems and leaves was affected by the application of HUMIRON (data not shown). The additional iron supply through HUMIRON enhanced fresh matter of stems and leaves in comparison with the control. The effect, however, was dependent on the type of HUMIRON® used. It seemed that Type R was more effective than type G. If no iron was added to the nutrient solution, the application of HUMIRON enhanced the fresh matter considerably. The application of low concentration of humates stimulated the leaf growth in the