Evapotranspiration of Agricultural Crops — Methods and Ассurасу оf Calculation

Abstract

Evapotranspiration of agricultural lands is а major factor in the water balance of the country in designing of irrigation and drainage systems and in the scheduling of optimal irrigation.
With proper preparation of thе field experiments, errors in evapotranspiration measurement (Еq. 1) are about 10-12%. In the same margins are the errors when using the FAO methodology (Allen, 1998) for evapotranspiration calculation.
On the basis of observations from 30 stations over the course of 30 years done by the collective Moteva, Kazandjiev and Georgieva (2008) thе values of reference evapotranspiration — ЕТ0 have been established. For the purposes of irrigation the most important data is the sum of the reference evapotranspiration for the months July and August. Based on this information we established that the country can be divided in 4 regions only. In them, the average evapotranspiration is 230 mm for Sofia region, 260 mm for North Bulgaria, 290 mm for South Bulgaria and 320 mm for the regions of Petrich and Haskovo. In the absence of precise lysimetric data, results obtained by field experiments or by FAO methodology can be used in irrigation practice.