Substrates used to grow plants have different origins and compositions and can be organic, mineral or synthetic materials. In the present work the effect of different water extracts (1:1.5; 1:2; 1:2'; 1:5; 1:5'; and 1:10) was evaluated and compared to saturated extracts for the determination of pH, electric conductivity, macro and micronutrients in commercially available products and some of their components. The results were compared to those with saturated extracts. Nine substrates were evaluated, recommended for the cultivation of tobacco, coffee, flowers (2), forestry species, citrus and horticulture species (3), and eleven substrate components: carbonized rice hulls, peat, fiber peat, vermiculite, perlite, Pinus bark compost (2), expanded clay, coir (coconut fiber), cork and 'xaxim' or 'samambaia-açu' (Dicksonia sellowiana). Chemical analyses were made in the substrate extract solutions for the determination of pH, electrical conductivity (EC), and macronutrient and micronutrient concentrations. The pH and EC data showed the lowest coefficients of variation. The micronutrient concentrations in the water extracts were very close to the equipment detection limits. The macronutrient concentrations showed coefficients of variation ranging from 5.1% to 47.2%. The method using the ratio 1:2 was better to obtain the saturation extracts for either macro or micronutrients. In spite of that, for all the other water extracts studied good results were obtained in the evaluation of pH, CE and macronutrientes in the tested samples.
substrates for plants; chemical analysis of substrates; macronutrients; micronutrients
