Useful Species Richness,Proportion of Exotic Species,and Market Orientation on Amazonian Dark Earths and Oxisols1

Useful Species Richness, Proportion of Exotic Species, and Market Orientation on Amazonian Dark Earths and Oxisols Anthropogenic soils of Amazonia, known as Amazonian Dark Earths (ADE), are environments with elevated soil fertility that can produce crops that otherwise yield poorly on the leached and highly acidic Oxisols that dominate much of the basin. While ADE sites near urban centers often attract commercial horticultural production of nutrient–demanding exotics, these soils are also considered possibly unique reservoirs of endemic agrobiodiversity because of their relationship to pre–Columbian indigenous occupation. Through botanical surveys and interviews with smallholder farmers, this study compared useful species richness, proportion of exotic species, and market orientation of farms situated on ADE and non–anthropogenic Oxisols in the municipality of Borba in Central Brazilian Amazonia. Species richness was similar on Amazonian Dark Earth and Oxisol farms (19.6 spp vs. 18.3 spp); however, ADE farms showed significantly higher proportions of exotic species (39% vs. 26%; p = 0.025). Furthermore, ADE farms in Borba demonstrated significantly higher market orientation (61.0% vs. 47.3%; p = 0.028), likely a result of the advantage of Amazonian Dark Earths for production of crops that are nutrient–demanding or pH–sensitive crops that have higher values in the nearby regional market of Manaus.