SOIL ENZYME-ACTIVITIES AFTER 1500 YEARS OF TERRACE AGRICULTURE IN THE COLCA VALLEY, PERU

Long-term productivity and conservation of soils is critical for sustaining agricultural ecosystems. Long-term sites can provide important information about the effects of soil management practices on soil properties but there are relatively few such sites available worldwide. The Colca Valley of Peru provided a unique opportunity to study the effects of 1500 years of cultivation on Mollisols. The specific objective of the work reported was to determine the effects of cultivation at this site on soil enzyme activity as an index of soil biology and biochemistry. The study compared three key soil enzyme activities (phosphatase, beta-glucosidase, and amidase) in presently cultivated and abandoned agricultural terraces, and matched uncultivated soils. Results showed that levels of organic matter, nitrogen and phosphorus were greater in agricultural than uncultivated soils. Unlike temperate regions where monoculture, intensive tillage and/or inorganic fertilizer practices have depressed soil enzyme activities, cultivated Colca soils have maintained similar or higher activities than the uncultivated/native soils. Maintenance of enzyme activities over hundreds of years in agricultural soils is partly attributed to traditional management practices including rotations with legumes, additions of animal manures, and minimum tillage.