Stomatal conductance and water use
Water use was calculated using the Penman-Monteith equation to estimate
transpiration rates. Some of the input variables required by this equation, including
net radiation, temperature, relative humidity and windspeed were measured directly
by an automated weather station situated at the site (Campbell Scientific Ltd. UK).
Stomatal resistance of component crops was measured using a steady-state porometer
(LI1600, Li-Cor, USA), whilst other variables (boundary layer resistance, vapour
pressure deficit and windspeed above the crop canopy) were derived using existing
ecophysiological models, as described by Rodrigo (1997).
Data analysis
Data were analysed using the SAS statistical package (SAS Institute Inc.,
Cary, NC, USA) and the Proc. ANOVA and Proc. GLM procedures for balanced and
unbalanced (i.e. for banana in which a different number of plants were harvested
according to the treatment) models, respectively. Data for each harvest were analysed
separately with the Randomized Complete Block Design, whilst pooled data of all
harvests were analysed with a model for the Split Plot Design in which each harvest
was considered as a sub plot (Roswell and Walters 1976). The relative performance
of component crops in different cropping systems were analysed in terms of Crop Performance Ratio. CPR (Azam-Ali et al, 1990), whilst Land Equivalent Ratio. LER.
(Willey. 1985) was used to evaluate the cropping system as a whole.