MINERALOGICAL CHARACTERIZATION OF THE RÍO NAPO FLOOD­ PLAIN ANO KNOLL SOILS

Abstract

The extent of research conducted in soils, mineralogy and pedogenetic processes in Ecuador is limited despite the country's unique geographic location and properties. The aim of the research is to provide mineralogical and physicochemical characterization of the soils in the northeastern quadrant of the Río Napo floodplains in order to better understand their (trans)formation history and the implications on nutrient dynamics and best agricultura! practices to protect the fragile eco­ system. Soils were characterized for texture, pH, percent organic matter and residual acidity in the laboratory. The < 53 µm fraction of the soil was further investigated using powder X­ray diffraction and FEG­SEM analyses. lnitial insights from three distinct regions (plinthic niti­ and ferralsols; fluvic ali­ and acrisols; arenic fluvisols) are reported and discussed. Ali­/acrisols and arenic fluvisols are dominated by primary feldspar minerals and muscovite with secondary mineral formation of kaolin­ ite, illite/smectite and vermiculite. Quartz is not dominant in sandy textured soils. Throughout the landscape plinthic niti­ and ferralsols protrude with dominant kaolinite­quartz­amorphous iron oxide mineralogy. These soils are very strongly acidic with significant acidification potential below pH 4, no organic matter and significant hardpan (plinthite) formation. In contrast the ali­/acrisols and flu­ visols in the region are moderately acidic with OM accumulations in the A horizon up to seven per­ cent. The substantial differences in mineralogical and physicochemical properties warrant future individual assessments of nutrient dynamics in order to support local farmers in their nutrient man­ agement.