Irrigation and Water Engineering Department, Chinhoyi University of Technology, P. Bag 7724, Chinhoyi, Zimbabwe
Jabulani, J., Irrigation and Water Engineering Department, Chinhoyi University of Technology, P. Bag 7724, Chinhoyi, Zimbabwe
The majority of farmers in Zimbabwe do not practice any form of irrigation scheduling at all. The few that schedule their crops mainly use the US Bureau Class A Pan evaporimeter. Techniques such as the use of tensiometers, neutron probes, electrical resistance blocks, Time Domain Reflectrometry and also such methods as the Penman-Monteith still remain within the domain of researchers, and may be just a few commercial farmers. The accuracy of the pan evaporimeter is dependent upon several factors which the majority of farmers fail to take cognizance of. A need to develop or try another method which can be easier to use by farmers has long been outstanding. The objective of this study was to evaluate the performance of the modified Jensen-Haise (MJH) model calibrated to the local conditions of Banket area in Mashonaland West Province of Zimbabwe. The results showed that the daily evapotranspiration rates estimated using the MJH model were less fluctuating than those measured using the pan evaporimeter. The two methods gave monthly and annual values of the evapotranspiration rate that were comparable (standard estimation error of 7.98% and 6.19% respectively). According to these results the MJH model calibrated for local Banket area can be used successfully for irrigation scheduling and also for hydrological modeling and planning. The study also revealed that the MJH model is strongly sensitive to air temperature. During winter, the MJH model gave values that were lower than those measured from the pan evaporimeter and during summer when temperatures are high, the MJH model proportioned evapotranspiration rates which were generally higher than those from the pan evaporimeter.