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Available online xxxKeywords: Evapotranspiration Growing degree days Spring wheat WUE HUE Neutron probe a b s t r a c t Estimation of actual evapotranspiration (ET a ) is an important part of agricultural water management in local and regional water balance studies. At the field scale, ET a is important in irrigation planning and scheduling and is an integral part of field management decision support tools. The conventional approach of estimating actual evapotranspiration is difficult and needs more calculations and extensive data on soil-plant-atmosphere. A field experiment was conducted to simplify the measurement and calculation of actual evapotranspiration by using thermal units (heat units) for spring wheat crop under trickle irrigation system in sandy soil. Two irrigation methods were applied; the first one (A) using the crop evapotranspiration (ET c ) that depends on whether parameters, and the second (B) is the depletion from field capacity which dependent on soil parameters. Three varieties of wheat namely Sids12, Misr2 and Gemmeza10 were cultivated on sand soil and treatments arranged in complete randomized block design with three replicates. Application of treatment (B) resulted in highly significant increase in yield production of Gemmeza10 and Misr2 as compared to treatment (A). Grain yield of different wheat varieties grown under treatment (B) could be ranked in the following descending order: Misr2 > Gemmeza10 > Sids12. While under treatment (A) it could be arranged in the following descending order: Misr2 > Sids12 > Gemmeza10. On the other hand, the overall means indicated non-significant difference between all wheat verities. The highest values of water and irrigation use efficiency as well as heat use efficiency were obtained with treatment (B). The equation used in the present study is available to estimate ET a under arid climate with drip irrigation system. journal h omepage: http :/ / www .e lsev ie r. co m/ lo cate/ j rras 1