APPLICATION OF ISO 11269-1 ROOT ELONGATION BIOASSAY FOR TESTING THE PHYSICAL PROPERTIES OF GROWING MEDIA

The ISO 11269-1 root elongation test is currently used for assessing soil quality and is known to be sensitive to soil texture. The aim of this study was to evaluate if the root elongation bioassay can be used to screen growing media, especially on the basis of physical properties, and if its results are comparable with that of other tests such as germination or growth. Results obtained from the application of the ISO 11269-1 test on 21 peat-based growing media coming from the Italian market, showed a wide range of values (from -70 to +90% of the control) indicating the high sensitivity of the bioassay to the root environment. Eleven growing media were also subjected to ISO 11269-2 plant growth bioassay on lettuce and to a germination test with cress and results were compared with those from the root elongation bioassay. Differences on seed germination of cress were detected only for one of the examined growing media. The growth test with lettuce strongly discriminated among products but in a different way from that of the root elongation bioassay, with four exceptions. Results indicated that both ISO 11269-1 and ISO 11269-2 bioassays were responsive to phytotoxicity and that they may be applied to growing media, the first to evaluate physical quality, the latter to estimate plant nutrient availability. Furthermore an attempt was made to develop a fast, simple to carry out and reproducible procedure (treatment of substrate and successive bioassay), responsive to the physical/structural stability of growing media during cultivation. For this purpose, the ISO 11269-1 root elongation test was carried out on eight growing media before and after they had been subjected to alternate drying and rewetting cycles in order to simulate growing conditions. Results showed a deterioration in the quality of four growing media (one peat mixture: two peat and sand mixtures: one sand, peat and clay mixture) caused by the repeated dehydration. The treatment did not affect the results of the bioassay on the other four growing media (one peat mixture: one peat and sand mixture: one peat and MSW compost mixture: one peat and green compost mixture). The preliminary data look promising for the development of the proposed procedure to estimate the impact of cultivation on physical/structural stability of growing media.