A comparison of modelled and measured millet production in northeastern Burkina Faso

Millet production has been monitored in the northern part of the Sahelian zone at the village Petakole located near Dori, NE Burkina Faso. Different methods, ranging from interviewing the local farmers to eddy covariance measurements of CO2-fluxes, have been applied for estimating the total biomass and grain yield. Using field measurements conducted in 1997, a mechanistic photosynthesis model was calibrated to suit the current, local environment. A comparison of the daily net assimilation measured by the eddy covariance method and modelled by the photosynthesis model shows that more than 85% of the day-to-day variation in assimilation can be described by the model. An analysis of the diurnal variation in CO2-fluxes over the growing season reveals that midday radiation load and leaf temperature are the most important climatic-hydrological parameters for predicting the carbon assimilation. At the end of the growing season when the soil moisture content is low (<8 vol.%) the rate of carbon assimilation is also limited by the stomatal control. For 1996 and 1997 the total CO2-uptake is compared to millet yield estimates (in kg m-2) obtained through interviews with the local farmers and using aerial photos and GPS for determining the field sizes. The estimated millet yields are found to be much higher for 1997 than for 1996 and in both years with a 25% difference between the two yield estimation methods.