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

Pre-Kispanic cultures constructed more than 82 000 ha of raised fields for agricultural production in the Lake Titicaca Region, in the current day Bol ivia and Peru. Raised fields consist of platforms (up to 1.2 m high and 2-2 0 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 rese arch was to obtain experimental information on a number of processes that m ight contribute to the frost mitigation effect. Field experiments were cond ucted at two sites in the Bolivian Altiplano. Temperature and moisture meas urements were made in plots where potato crops were grown. Minimum temperat ures during clear nights with fairly calm wind conditions were about 1 degr ees C higher at 50 cm above the soil surface in the middle of raised field platforms compared to adjacent flat fields, confirming earlier reports. Dif ferences in minimum temperatures tended to increase with wider canals, wher eas a change of platform width from 4 to 6 m had no appreciable effect. Tem perature and moisture distributions in platform/canal cross sections sugges t that the frost mitigation effect is due mostly to above-ground processes. Specifically, air circulation from canal to platforms, arising from natura l convection, and cold air drainage back to the canals satisfactorily accou nt for observed temperature differences. These results should prove useful in the design of raised fields and of physical process-based models to simu late the frost mitigation effect. (C) 1998 Elsevier Science B.V. All rights reserved.