OPTIMALIZATION OF OXYGEN LEVELS IN ROOT SYSTEMS AS EFFECTIVE CULTIVATION TOOL

To investigate the influence of oxygen concentrations in the root system on plant development, young cucumber plants were grown during three weeks on stone wool blocks. A continuous flow of nutrient solution (0.75 L h^-1), containing 0.5, 3.5 or 10 mg L^-1 dissolved oxygen, was led through the substrates. Already after 3 days, the impact of the various oxygen levels in the root systems became evident. Plant development was reduced when plants were subjected to the lowest oxygen concentration. In time, increasing differences in leaf area were observed when plants were grown under different oxygen levels, showing largest leaf area at 10 mg L^-1 oxygen. Also, root mass was significantly reduced when plants were grown under low oxygen conditions. Bacteria and other micro-organisms that consume oxygen can reduce oxygen levels. Oxygen consumption was detected in samples that were taken at different places in greenhouses, e.g. irrigation water storage tanks, irrigation supply system and substrates. During the winter period, the contribution of micro-organisms in oxygen consumption was low. However, in April oxygen consumption in the samples was significantly higher. Sometimes, oxygen in nutrient solution, present in the substrates, was fully consumed within 30 minutes, indicating that roots would suffer anoxia. Frequent refreshment of nutrient solution in the irrigation supply system had a major impact on oxygen levels. Continuous measurements showed that during the day oxygen levels in the irrigation system were high just after refreshment of the nutrient solution, but between two refreshments oxygen levels in the system dropped towards very low oxygen values. If technically feasible, in future the control of oxygen levels in root systems may become a new tool for growers to manage cultivation in horticulture, in addition to light, temperature, carbon dioxide, nutrition and water.