Bulletin de l'Institut Français d'Études Andines (Sep 2003)
La Mitigación de heladas en los camellones del altiplano andino
Abstract
The raised fields system is an old technique of soil and water management, which was very frequent in the Lake Titicaca region before the Spanish conquest. It essentially consists of a series of earth platforms surrounded by water canals. Crops are grown on the platforms and water level in the canals is controled through inlet and outlet ditches. An important and widely recognized benefit of this system of management is its contribution to frost mitigation during the growing season. An experiment has been conducted on a system of raised fields in the Lake Titicaca region with the goal of quantifying the phenomenon and specifying the physical processes responsible for the mitigation effect. A potato crop was grown on the platforms of the raised fields and the same crop was grown on a control plot in the “Pampa”. Experimental results show that during the night: (i) water temperature is much greater than the temperature of the crop on the platforms; (ii) crop temperature is always greater (1-2 degrees) on the platforms than on the control plot in the Pampa. A physical process-based model, adapted from a two-layer transfer scheme of the Shuttleworth-Wallace type (a vegetation layer and a substrate layer of water), is presented to explain the mitigation effect. The model specifies the role played by the canals in the nocturnal heat dynamics and the night-time variation of crop temperature. The mitigation effect is due to heat emanating from the canals and to water condensation on the leaves. When used in a predictive way, the model shows that wider canals and narrower platforms have a positive impact on the minimum crop temperature reached during the night. Increasing water depth also negative impact. Leaf area index (LAI) and crop height, both have a positive impact on frost mitigation. The marginal benefit, however, is very small when LAI is greater than 1. Higher wind velocity or higher air relative humidity also enhances the frost mitigation effect.
Keywords
