Lixiviação de nutrientes, elementos-traço e tiametoxam em solos com cafeeiro, sob efeito do uso sucessivo de lodo de esgoto

Abstract

The use of sewage sludge in agriculture has benefits such as the incorporation of the nutrients and the improvement of physical and chemical soil properties, in addition to allowing the recycling of this byproduct of sewage treatment, of which the amount tends to increase in large scale. However, we cannot underestimate the possibility of nutrient and trace element leaching as well as the contamination of water resources at the locations in which it is applied. In addition, if the application of this residue occurs conjointly pesticides, it can interfere with sorption or even increase the carrying of pesticide molecules in the soil profile. Therefore, the objective of this study was to evaluate the leaching of nutrients, trace elements and thiamethoxam in dystrophic Yellow-Red Latosol (YRL), dystroferric Red Latosol (RL) and dystrophic Yellow-Red Argisol (YRA) cultivated with coffee, under the effect of successive applications of sewage sludge. The experiment was conducted on a set of lysimeters containing undisturbed material of the aforementioned soils. The sewage sludge, in both years, increased fundamental attributes of soil fertility, such as cation exchange capacity and organic carbon, however, it reduced pH and increased exchangeable aluminum. This residue also increased the contents of Cd, Cr, Cu, Pb and Zn in the studied soils. The sewage sludge reduced the growth and productivity of coffee in the studied soils, but increased the contents of Cu, Zn and Cd in the husks of the coffee fruit. We also observed higher levels of Cd in the coffee fruit seeds, in the three of the studied soils, and higher levels of Zn and Pb in coffee seeds cultivated in RL. Furthermore, there was increase in the amount of nitrate, calcium, magnesium, potassium and sulfate leachate in the studied soils. However, there was no effect of the dose of sewage sludge in the amounts of cadmium, chromium and lead in the leachate of YRL and RL, but there was effect of the same in the leachate of the YRA. The thiamethoxam insecticide was highly leachable in the studied soils, maintained with coffee and under natural rainfall, in such a manner that the application of thiamethoxam on these soils resulted in the leaching of significant amounts of the compound below 0.90. Therefore, under practical conditions of thiamethoxam use in the studied soils, the risk of groundwater contamination with residues of this compound are high. Furthermore, the application of sewage sludge on RL and YRA increased the amount of leached thiamethoxam.