GAS CONCENTRATION IN THE ROOT ZONE OF ROSA HYBRIDA L. GROWN IN DIFFERENT GROWING MEDIA

The subject of this study was to get more information about the root zone, mainly the gas composition in growing media, which is used in hydroponic systems. Besides the plant growth parameters of roses, yield and nutrient uptake, the results of the gas concentrations in the root zone are presented. Gas sampling at 2 or 3 heights from root zone did function well, results ranged from 530 ppm to 1570 ppm CO₂. Results are significant between the different substrates and measurement spots within one substrate. The organic substrates “Coir” (coconut fibre) contains most CO₂. From top to the bottom the CO₂ level was increasing. The CO₂ level is influenced by microbial and root respiration. But compared with recommended figures the determined CO₂ concentration is no limiting growth factor. The O₂-concentration in substrates was determined between 39 % to 99 % saturation of disolved oxygen (DO). The daily time course was for each substrate different and specific. The results shown a influence by the plant activity (radiation) and the irrigation schedule. The Coir substrates contained with about 40 % significant less oxygen than inert substrates (Perlite, Grodan and Sawagrow). O₂-level of substrates can be an indicator for oxygen deficiency direct in root zone. During the experiment the O₂-concentration decreased from the top to the bottom of substrates; for CO₂ the opposite trend was found. The new method of monitoring the oxygen level in substrates via fiber optic sensors did function well. The artifact of oxygen deficiency correlating with low yield or quality wasn’t found during the experiment. Experiments should be continued with different oxygen levels in substrates due to excess irrigation or substrates with high water content levels to get deficiency conditions for plants roots and significant results.