Modelling water dynamics in coffee systems: Parameterization of a mechanistic model over two production cycles in Costa Rica

Coffee (Coffea arabica) is one of the most economically important agricultural crops in Central America where it is generally grown under shade trees. In Costa Rica, large amounts of fertilizers, particularly nitrogen, are applied under intensive coffee cultivation with potential harmful contamination of groundwater. Shade trees improve coffee soil fertility, but can provide some disadvantages such as competition for soil water, notably during the dry season. Consequently, modelling the water balance is essential in order to predict water fluxes, particularly water drainage and possible water table contamination. Thus, the objective of this study was to calibrate a mechanistic model in order to simulate and compare the water fluxes over two consecutive years in two coffee agrosystems with shade of Inga densiflora and in full sun, in the Central Valley of Costa Rica. To do so the following field and laboratory measurements were taken: i) soil water content monitored by TDR measurements over the 2 production cycles; ii) soil properties at various depths, including bulk density, soil retention curve and saturation hydraulic conductivity; iii) meteorological data and calculated ETP; iv) water consumption of coffee and trees; v) rainfall interception by the canopy of shade trees and coffee plants; vi) trunk flow of coffee and shade trees; and vii) surface runoff. The model satisfactorily simulates soil water content over the year at different depths down to 200 cm. The model also simulates the dynamic water partitioning between components of the coffee system (vegetation transpiration, soil water content, runoff) and hence can be a useful tool in recommending selection and management of shade trees with respect to rainfall and soil water availability. Furthermore, this work permits the calculation of the amount of water drainage and hence provides a sound basis for calculation of nitrate leaching out the system into the sub-soil and aquifers. (Texte intégral)