MODELLING BIOMASS AND BULB YIELD OF ONION (Allium cepa) UNDER DIFFERENT IRRIGATION REGIMES USING THE AQUACROP MODEL

Abstract

Crop water productivity models are important tools in evaluating the effect of different irrigation regime on crop yield. AquaCrop model is a crop water productivity model adopted by the Land and Water Division of FAO in the year 2009. It simulates yield responds to water for herbaceous crops, and it is particularly suitable in addressing conditions where water is a key limiting factor in crop production such as in northern Ghana. The objective of this study was, to calibrate the AquaCrop model for different irrigation regimes for onion (Allium cepa), to determine its effect on crop growth and yield parameters of the crop at the Bontanga irrigation scheme. This was done by determining the crop and economic water productivity for each irrigation regime of onion. To achieve these, the Randomised Complete Block Design (RCBD) was used on Red Creole onion variety. Randomised Complete Block Design was made up of four irrigation treatment regime of 117%, 100%, 80% and 60% of the crop water requirement of onion with five replicate blocks. Results indicated that there was no significant variation in yield, dry bulb biomass and total biomass, but there was difference for dry leaf biomass of onion at 0.05 level of significance. Results also showed that crop water productivity and economic water productivity of onion increases with increasing irrigation deficit, whereas evapotranspiration water productivity of onion increases with increasing irrigation regime. The AquaCrop model simulated satisfactorily the crop yield, biomass and evapotranspiration water productivity of onion. There was a strong correlation and a significant linear relation between the simulated and measured crop yield, biomass and evapotranspiration water productivity. Validation of AquaCrop model using Nash-Sutcliffe efficiency (E), Root mean square errors (RMSE) and index of agreement (d) showed that, AquaCrop model can therefore be used to simulate bulb like crops such as onion.