315 Total Element Concentration Quantification in Substrates M.F. Abreu, Â.M.C. Furlani, C.A. Abreu and P.H. Santos Instituto Agronômico Campinas, (SP) Brazil A. Paz-Gonzalez Facultad de Ciencias Campus A Zapateira, La Coruña Spain Keywords: heavy metals, acid digestion, microwave digestion, nitric-perchloric digestion, macronutrients, micronutrients Abstract Substrates for plants may present varied composition, from a single component to a complex mixture of different materials, which may present low, adequate or high plant nutrient concentrations. Some substrates, depending on the origin, may present high heavy metal concentrations. The determination of total element concentrations for the chemical characterization of these materials turns an important issue not only for fertilizer recommendation but also for quality control. The objective of this research was to evaluate the total concentrations of some elements in Brazilian commercial substrates using two heating processes, as well as to investigate the levels of heavy metals, which are related to the quality of the material. Nine organic substrates and one inorganic, commercialized in Brazil, were used for the determination of total- P, K, Ca, Mg, S, Na, Cu, Fe, Mn, Zn, Cd, Cr, Ni and Pb concentrations, using two digestion procedures (open system acid digestion and microwave-oven digestion. For P, K, Ca, Mg, Na, Mn, Zn and Cr the total element concentrations were very similar irrespective of the technique used, with angular coefficients close to 1.0. On the other hand, for S, Cu, Fe and Cd there was a variation above 20% in the total element concentrations. The nitric-perchloric digestion extracted around 26% more Cu when compared with nitric- microwave method. An opposite tendency was observed for the elements S and Fe, since the nitric-microwave procedure presented 21 to 29 % larger extraction, respectively. Total heavy metals determination is recommended for monitoring the composition of substrates used in agriculture. INTRODUCTION The substrate production in Brazil is an emerging segment that has demonstrated excellent growth and development capacity in the last few years. In spite of the lack of performance numeric indicators, a short survey among some of the more expressive Brazilian substrate producing companies, suggests that the attended demand for this product in the country is around 600 to 700 thousand cubic meters per year for an estimate total demand of 1.5 million cubic meters. There are about 30 to 40 well- established and structured companies, which nowadays are still adjusting technological production processes (Kampf, 2002). Substrates present varied composition, from a single component to a complex mixture of different materials and origins such as: mineral - (vermiculite, perlite); organic - (peat, chopped tree bark, composted or not, other vegetal fibers, etc.) or synthetic - (phenolic foams) (Kampf, 2002). Moreover, substrate use in agriculture is an opportunity for the general recycling of agro-industry (agro-factories) residues what turns it attractive under the environment preservation stand point of view. In the substrate formulation several components utilized may present low, adequate or high plant nutrient concentrations. Some substrates, depending on its origin, may present high heavy metal concentrations (Abreu et al., 2000), causing toxicity to plants, animals and eventually to men. Thence, the determination of total element concentrations for the chemical characterization of these materials turns an important issue not only for fertilizer recommendation but also for quality control. Proc. IS on Soilless Cult. and Hydroponics Ed: M. Urrestarazu Gavilán Acta Hort. 697 ISHS 2005