The impact of high-intensity no-till agriculture on groundwater quality in the subtropical Capiibary catchment, SE Paraguay

The Capiibary catchment, SE Paraguay, forms part of the Guarani Aquifer System and is intensively used for cashcrop agriculture (soy bean, wheat, maize), with two or more harvests per year. The aim of this study was to investigate the effects of no-till agriculture with frequent herbicide and fertilizer applications on groundwater quality under subtropical climate. Water samples taken from 81 wells showed rather low nutrient (e.g. nitrate) concentrations, probably due to the high humus content of the no-till soils and the prevalent climatic conditions which allow constant microbial recycling of nutrients. The denitrificaton potential of the aquifer is, however, small. Further analysis in seven wells showed no indication of pesticides in groundwater. This is probably attributable to a combination of the effects of no-till agriculture and the subtropical climate.