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

Long-term productivity and conservation of soils is critical for susta ining agricultural ecosystems. Long-term sites can provide important i nformation about the effects of soil management practices on soil prop erties but there are relatively few such sites available worldwide. Th e Colca Valley of Peru provided a unique opportunity to study the effe cts of 1500 years of cultivation on Mollisols. The specific objective of the work reported was to determine the effects of cultivation at th is site on soil enzyme activity as an index of soil biology and bioche mistry. The study compared three key soil enzyme activities (phosphata se, beta-glucosidase, and amidase) in presently cultivated and abandon ed agricultural terraces, and matched uncultivated soils. Results show ed that levels of organic matter, nitrogen and phosphorus were greater in agricultural than uncultivated soils. Unlike temperate regions whe re monoculture, intensive tillage and/or inorganic fertilizer practice s have depressed soil enzyme activities, cultivated Colca soils have m aintained similar or higher activities than the uncultivated/native so ils. Maintenance of enzyme activities over hundreds of years in agricu ltural soils is partly attributed to traditional management practices including rotations with legumes, additions of animal manures, and min imum tillage.