ABSTRACT

In this study, modified Blaney-Criddle method was adopted to evaluate the potential evapotranspiration data of National Root Crop Research Institute Umudike. This involve maximum and minimum daily temperature data, percentage of possible sunshine hour for 1 Oyrs (2000-2009) respectively and crop coefficient using grass as a reference crop. The value of monthly PET by modified Blaney-Criddle method was obtained when the mean temperature was seen to be 32/23°C, mean daily percentage (%) sunshine hours of 6.4/4.3 using statistical analysis and crop coefficient of 0.65 for grass. This indicates that the seasonal mean for rainy season evapotranspiration is 155.8mm/month and for dry season 222.8mm/month. While the actual total monthly mean of 178.2mm/month was obtained by multiplying the empirical formula of Blaney-Criddle with mean temperature and percentage daily sunshine hours. Potential evapotranspiration PET = Uc (consumptive-use) was obtained by multiplying the actual evapotranspiration by the crop factor of 0.65. The seasonal mean for rainy season is 101.4mm/month and dry season 144.9mm/month with annual total mean of 115.9mm/month. Indicating that at a particular month in the season, crop will suffer moisture deficit of a magnitude of 22% during march-may to about 56% in November to February period, while a mean value of 145mm of the total water needs ofthe crop is utilized during critical stages.