Anthropogenic soils from Llanos de Moxos (Bolivia): Soils from pre-Columbian raised fields

Raised field cultivation (camellones) is a Pre-Columbian technique, now abandoned, which is very extensive in the Llanos de Moxos (Bolivia). The objectives of the research were to understand the effects of human actions on the morphology, genesis and characteristics (especially redoximorphic features and chemical properties) of these soils on ridged fields and their past use. We studied five representative raised field (anthropogenic) soils and other non-anthropogenic soils around San Ignacio de Moxos and along the transect Trinidad-San Borja. The non-anthropogenic soils are acidic, show a wide range of clay contents and different degrees of human activity according to their available phosphorus content. Soil-forming processes are related to fine fraction mobility and alternating redox conditions. Contrarily, the soils of the raised fields show a distinct pattern of redoximorphic features from ridge to channel. Moreover, ridges tend to be less acidic and have lower aluminium saturation than channels. Nevertheless, they have neither artifacts nor charcoal, and their colour and P content is similar to those of surrounding soils. The raised fields appear to have been built to improve the drainage conditions. Chemical soil fertility was not the main issue and they were used for cultivation including maize. The set of characteristics encountered (differences in pH, and drainage status at a microscale) should be used to improve the classification of these anthropogenic soils.