Abstract

LEMEILLET, Fabián et al. Electrical conductivity of a soil treated with effluent from livestock. Geoacta [online]. 2016, vol.41, n.2, pp.57-73. ISSN 1852-7744.

The presence of contaminants in the soil implies the existence of potential adverse effects to humans, plants and animals, and the ability of them to be transmitted to groundwater, may also affect remote ecosystems. Livestock effluents are a source of diffuse pollution from runoff of manure from intensive animal production farms. Geophysics, particularly geoelectrical method, measures the electrical conductivity (EC). With EC, salinity areas may be determined. The objective was to identify contrasts of EC values associated with the presence of nitrate salts derived from livestock effluent mineralization. The study was a small scale trial on experimental plots with a previous fertilization with cattle manure. Electrical resistivity tomographies were carried out at the plots in two instances with different soil moisture condition (Year 1 and Year 2). The observed data of ECa (apparent electrical conductivity) were processed using a software 2D, obtaining for each plot a model of distribution of true soil EC. The models allowed observing that only for the year of higher edaphic humidity (Year 1) there was a positive correlation between the manure loads and the EC of the corresponding models. For the specific analysis of the EC and nitrate salts relationship, within each plot four sectors were sampled, nitrate concentrations were obtained and these were related to EC models for the same sites. The highest correlations also occurred in the first year plots. In Year 2, characterized by low soil moisture and the presence of highly resistive air zones, there were large contrasts of CEa within the plots that would have produced noisy results in the models, conditioning the efficiency of electrical resistivity tomography, this year. Additionally, when CEp (electric conductivity in saturation paste) data were taken at the head of each plot, it was compared with the CE of the respective model for that same site. For Year 1, both variables correlated with R2 of 85%, and for Year 2, the adjustment was moderate (55%). The efficacy of electric tomography for the detection of salinity from organic matter mineralization is influenced by water content and soil cracking, but in general terms it can be pointed out that the methodology can contribute to a diagnosis of the content of nitrate salts.

Keywords : Geoelectrical method; Livestock effluents; Pollution; Electrical conductivity; Electrical resistivity; Electrical conductivity in saturated paste.

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