Effects of lactate, humate and Bacillus subtilis on the growth of tomato plants in hydroponic systems

Investigations were carried out with the view to getting a more balanced nutrient supply in hydroponic systems and better plant resistance against influence of stress factors. Organic and biological agents based on humic and lactic acids were added to the nutrient solution. They were expected to improve the resistance of tomato plants particularly under stress conditions. Stress factors were chosen that are of major concern in hydroponic systems: suboptimal pH values and suboptimal electric conductivity (EC). Humic acid was applied in the form of sodium humate, and lactic acid was applied as lactate (LACTOFOL). The latter has been designed as a suspension leaf fertilizer based on waste material from the dairy industry. Tomato test plants were cultivated in perlite substrate mostly until they had eleven or twelve leaves, and in one of the experiments they were investigated until they produced fruit. The following general conclusions have been drawn: Humic acid and LACTOFOL produced specific effects at different pH and EC values. Depending in their concentration and frequency of application, organic agents may either stimulate or inhibit plant growth. Humic acid improved plant growth when the EC was very high. When humic acid had been applied by watering the substrate, shoot and root dry matter as well as root length were higher with optimal pH (5.8). In almost all experiments with pH between 4.5 and 7.5 better growth parameters were recorded when LACTOFOL had been added to the solution. LACTOFOL was particularly effective in high-pH solutions. In some cases the development of tomato plants was also enhanced by combinations of humic acid, LACTOFOL and/or Bacillus subtilis.