The main cause of disturbances in proper nutrient uptake and distribution by plants grown in inert media is an increase of some nutrients in total ion concentration (EC) in the root environment. This phenomenon results from increased water uptake relative to nutrients and ballast ions. The aim of the present study, conducted in the period 2007–2008, was to determine changes in the nutrient contents of the root environment and leaves of tomato grown in expanded clay being post-production waste in soilless tomato culture under extended cycle conditions. The study used new expanded clay (I) as the control and expanded clay being post-production waste from year-round tomato cultivation with the following experimental design: chemically sterilized material (II); material washed in water with the remains of the old root system of plants removed and additionally chemically sterilized (III); and material without any modifying treatments (IV). Expanded clay was placed in 12 dm³ poly sleeves and formed in the shape of growing slabs. Crops were grown using a drip irrigation and fertilization system with closed nutrient solution system, without recirculation. The nutrient solution was supplied to all plants in the same amount and with the same composition. The study did not find significant differences in the content of mineral nitrogen, phosphates, potassium, calcium, manganese, iron, and zinc in the root environment of plants grown in new and reused expanded clay. Changes in total ion concentration (EC) in the root environment of plants during growth did not differ significantly between the investigated treatments. The adverse phenomenon of alkalization of the root environment, characteristic for new expanded clay, was not found in expanded clay being post-production waste reused as a growing medium. The study did not find significant differences in plant nutrition which might prove that expanded clay under study cannot be reused as a growing medium in plant cultivation.

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