Document Type: Research Paper
Department of Agricultural Engineering, Federal University of Technology, Akure, Nigeria
Water flux in a young, 4-year old, cashew (Anacardium occidentale L.) plantation was studied over a dry season, from November 2001 to March 2002, in the forest-savannah transition zone of Ghana, West Africa. The temperature-difference method was used over this five-month period to quantify the diurnal and day-to-day whole-tree sap flow (Qt) and hence the canopy scale transpiration (Ec). Measured allometric data were used to convert sap flow to canopy transpiration, while the observed meteorological variables were used to derive canopy scale conductance (gc) by inverting the Penman-Monteith equation. Sap flow varied between 9 and 22 kg day-1 and was on average Qt = 14 kg day-1 for the entire period. Tree sap flow was closely dependent on solar radiation and less dependent on air vapour deficit. Using no time shift, sap flow was fitted to a simple equation that showed its parabolic response to global radiation. The estimated average diurnal pattern of gc ranged from 0.1 to 2.2 mm s-1 while aerodynamic conductance (ga) ranged from 21.9 to 49.3 mm s-1. This result is expected to be of value in the analysis of atmospheric control of canopy transpiration in orchards in West Africa.