Heat and moisture dynamics in raised field systems of the lake Titicaca region (Bolivia)

Abstract

Pre-Hispanic cultures constructed more than 82 000 ha of raised fields for agricultural production in the Lake Titicaca Region, in the current day Bolivia and Peru. Raised fields consist of platforms (up to 1.2 m high and 2–20 m wide), elevated relative to the original soil surface and surrounded by canals (1.6–4.5 m wide). In the last decade, archaeologists have promoted the adoption of raised fields among local farmers as a way to reduce potato ( Solanum tuberosum) crop damage caused by mid-growing season frosts in the Altiplano (3800–4000 m above sea level). The objective of the present research was to obtain experimental information on a number of processes that might contribute to the frost mitigation effect. Field experiments were conducted at two sites in the Bolivian Altiplano. Temperature and moisture measurements were made in plots where potato crops were grown. Minimum temperatures during clear nights with fairly calm wind conditions were about 1°C higher at 50 cm above the soil surface in the middle of raised field platforms compared to adjacent flat fields, confirming earlier reports. Differences in minimum temperatures tended to increase with wider canals, whereas a change of platform width from 4 to 6 m had no appreciable effect. Temperature and moisture distributions in platform/canal cross sections suggest that the frost mitigation effect is due mostly to above-ground processes. Specifically, air circulation from canal to platforms, arising from natural convection, and cold air drainage back to the canals satisfactorily account for observed temperature differences. These results should prove useful in the design of raised fields and of physical process-based models to simulate the frost mitigation effect.