Experiments started out to investigate the effect of humates in hydroponic systems on the growth of tomato plants. Investigations were carried out by using different substrates (perlite, coconut-fibre and peat-based substrates) and in small tanks as water-culture. In some experiments were compared concentrations and forms of humic acids (K-, Na- and NH4-humates). Moreover were investigated the influence of humates on the germination of tomato seeds. It was analysed the influence of treatments with humates on the nutrient uptake of tomatoes. Tomato test plants were cultivated in containers with different substrates or tanks with nutrient solution until the plants had three inflorescence and they produced crop. In some experiments tomato plants were cultivated until they had eleven or twelve leaves. The 'Hydrofer' computer program was used for calculating the amounts of fertilizers, salts and acids required. It was analysed fresh and dry matter of the plants, root length, sugar content in tomato fruits and the content of nutrients in leafs and fruits. The following conclusions have been drawn: 1. Treatments with humic acid showed a positive influence on the germination of tomato seeds. 2. Effects on the plant growth depends of the humate form and material used for the extraction (peat, coal). 3. Humic acid improved plant growth depending on the concentration and frequency of treatments and the air-capacity in the rhizoslohere. 4. Humic acid has an influence on the length of roots and shoots. 5. The content of nutrients as Ca and K were influenced by treatments with humic acid, but different in leafs and fruits.
