Soil quality in key pedogenic regimes of interandean Ecuador
Variables reflecting soil quality, including OM content, mineralogy, nutrient content, porosity, texture, pH and soil fauna content, were examined in key pedogenic regimes of northern interandean Ecuador. Soils under non-technical agriculture were collected along the Urumbilla interfluve of Imbabura while soils under semi-technical agriculture were collected in the potato producing region of San Gabriel, Carchi. In Urumbilla, high elevation, steeply sloping, non-cultivated soils experiencing a cooler, wetter climate were found to be black and acidic, containing low levels of glass and plagioclase minerals. The mid-elevation, moderately sloping, cultivated soils under non-technical agriculture were yellow to dark brown, containing hard cemented layers. These soils exhibited a more severe degradation in soil quality than soils at higher and lower elevations, as they contained the lowest levels of OM, NH4 +, P, PSR, silt and soil fauna. Erosion appeared to be accelerated in the mid-elevation zone, as indicated by the lower levels of P, OM and silt, as well as the existence of a subsurface soil differing in mineralogy from the high- and low-elevation zones. The low elevation, flat-relief soils experiencing a warmer, drier climate were the most basic in nature and contained the highest levels of K, plagioclase and glass. In San Gabriel, soils under semi-technical agriculture were found to be black, acidic and rich in OM and available nutrients. These soils exhibited higher OM, nutrient, PSR and soil fauna levels than comparable non-technical, Urumbilla soils. The San Gabriel soils which had been under cultivation for the shortest time period contained only topsoil in their upper 1 m and exhibited the highest OM, P and silt levels. Soils under longer-term cultivation recently used for potato production contained a sandy subsoil within their upper 1 m. This decreased topsoil thickness suggests greater soil losses by mechanical erosion have occurred at these sites. Finally, soils under pasture were observed to contain higher soil fauna levels than soils under potato production. As a wide variety of deficiencies and concerns were found in the different pedogenic regimes of the Ecuadorian Andes, site specific management is needed to properly address the diversity of problems in the different areas.