Soil solution chemistry of a Brazilian Oxisol irrigated with treated sewage effluent

Irrigation is considered as a good alternative for sewage effluent use with the actual concerns for increasing use of water in agriculture, and the decreasing supply of good-quality waters, particularly in tropical countries. The irrigation management with sewage effluent must carefully be done, and impact of such practice on soil and environment-quality has to be well known. Short-term effects of effluent on soil are expected to be identified by soil solution chemistry changes. Therefore, the aim of the study was to evaluate the variation in soil solution chemistry during the irrigation of maize and sunflower crops with sewage effluent in a Brazilian Oxisol. For this, soil solution chemistry was monitored during 2 years by porous ceramic cups from the surface to 200 cm soil depth. The high content of bicarbonates and sodium in effluent induced soil solution sodification and alkalinization, with a total input of 2.44 tonnes of Na+ and 4.40 tonnes of HCO3-. Partial leaching by dripping irrigation led to an increase in pH, sodium adsorption ratio (SAR) and electric conductivity (EC) within the upper soil meter. It was also identified a decrease in Na+ along time that was attributed to both leaching and opening of soil exchange complex by Na+-induced tactoids expansion. The high Na+ input had little influence on calcium concentration that remained constant but relatively low, as expected in tropical soil. Results about C and N chemistry showed mineralization of dissolved organic matter and rapid nitrification from ammoniac and organic nitrogen provided by effluent. The nitrate concentration decreased by plant uptake but also by leaching during the rainy season, pointing out a long-term risk of contamination of shallow groundwater environments. (c) 2006 Elsevier B.V. All rights reserved.