Use of new soilless growing media with attention for nutrient balance in the plant tolerance test

Major knowledge on soilless growing media and soilless culture is based on peat. To develop successful growing media with less peat, it is important to know and understand the behavior of raw materials in the growing media. One of the chemical aspects to be considered is nutrition. Due to limitation by physical aspects, it is not possible to test plant tolerance in a pot test with high dosage mixtures of wood fiber, vermiculite, or bark. Extracts of the components can be used for testing plant tolerance if there is a balanced nutrition. Extracts according to the European plant response Standard (EN 16086-1) with nutrient solution were prepared of bark, wood fiber, husk chips, wood fiber/husk chips mixture (50/50 v/v) and vermiculite and adsorption/ desorption of elements was determined. The actual load of elements in the components bark and vermiculite was tested by extraction with calcium chloride/DTPA (further named CAT, EN 13651), water (EN 13652) and sulphuric acid (0.05 M). Ion exchange of vermiculite in sulphuric acid was higher than in CAT. It is advised to use results of the extract test with nutrient solution and knowledge on cation exchange to determine adjustments for the solution to be used for preparation of an extract for testing plant response. By adjustment unbalanced nutrition during testing can be prevented.