ANCIENT AGRICULTURAL SOILS IN THE ANDES OF SOUTHERN PERU

Knowledge about soil changes resulting from long-term agriculture is i mportant because agricultural influences on soil continue to increase in extent, intensity, and duration. Agricultural terraces in the Colca Valley, Peru, present an opportunity to study soils that have been cu ltivated for at least 15 centuries. Physical and chemical properties o f soils were determined to explore possible effects of traditional agr icultural practices on soils. Relative to nearby uncultivated Mollisol s, agricultural A horizons are commonly 0.3 to 1.3 m thicker, contain buried organic-matter-enriched horizons, and are lower in bulk density . They also have more organic C and N and lower pH. Cultivated A horiz ons, particularly in agricultural terraces that have been abandoned fo r about four centuries, are enriched in P. Data suggest that P applied as fertilizer has been translocated deeply into soils during centurie s of agriculture and accumulated in physically undisturbed B horizons. Agricultural practices inferred to be causal factors in changing thes e soils include terracing, tillage, fertilization, and irrigation. The se ancient agricultural soils contain features characteristic of anthr opic and plaggen epipedons and agric horizons.