Evaluating Reference Crop Evapotranspiration of the Selected Field Crops Grown in Different Agricultural Regions in the Vietnamese Mekong Delta

The water balance in six selected crops (mung beans, tomatoes, maize, cassava, yam, and sweet potatoes) was determined at the field block scale in the Vietnamese Mekong Delta for two agricultural growing areas. A novel approach for the calculation of water balance was employed, which combined the reference crop evapotranspiration (ETo), derived from four methods, namely, Penman-Monteith, Blaney-Criddle, Thornthwaite, and Turc. The equation of Penman-Monteith is generally considered to be the most representative to calculate the ETo value. The reference crop evapotranspiration for some crops was calculated. The daily ETo ranges from 1.8 to 7.5 mm, while a monthly ETo ranges from 3.5 to 5.0 mm. The calculations of the water balances show that irrigation is necessary for crops grown on raised beds crops during the dry season. The results show a promising approach for evaluating the water regime to satisfy crop water requirements.