Resumo

VELAZCO, K et al. Evaluation of nitrates and nitrites leached under an intensive grazing system using nitrogen fertilizer. Rev. Fac. Agron. [online]. 2009, vol.26, n.1, pp.23-38. ISSN 0378-7818.

Subterranean waters pollution by nitrates and nitrites coming from agricultural activities is a big problem at world level, so, in this study the levels of nitrates and nitrites below the root zone were evaluated in an area under Marandu grass (Brachiaria brizantha) on a sandy loam soil with an intensive management system, in the region of "Las Jabillas" Machiques de Perijá municipality (Zulia State-Venezuela), a dry tropical forest life zone. Twelve observation wells (lysimeters) were installed to take samples once a week during eight weeks and samples were also taken in wells near the study area. The experimental design was completely at random. The nitrate concentrations obtained from the analysis of the samples were all between 0.09 and 4.13 mg.L^-1 and thus below the limits established for water for human consumption by the Environmental Protection Agency and the World Health Organization (WHO). According to the Duncan-Walles test, there are significant differences between the lysimeters of this study related to their position within landscape and drainage condition of soils. Water in wells that is used for human an animal consumption has not been affected by the indiscriminate use of nitrogen fertilizer that is part of the intensive pasturing management system and cattle breeding.

Palavras-chave : nitrates; nitrites; leaching; intensive management system.