Water use pattern and canopy processes of cashew trees during a drying period in West Africagoo

Abstract

Water flux in a young, 4-year old, cashew (<em>Anacardium occidentale </em>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 (<em>Qt</em>) and hence the canopy scale transpiration (<em>Ec</em>). Measured allometric data were used to convert sap flow to canopy transpiration, while the observed meteorological variables were used to derive canopy scale conductance (<em>gc</em>) by inverting the Penman-Monteith equation. Sap flow varied between 9 and 22 kg day^-1 and was on average <em>Qt</em> = 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 <em>gc</em> ranged from 0.1 to 2.2 mm s^-1 while aerodynamic conductance (<em>ga</em>) 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.