A. Matev, R. Petrova, H. Kirchev

Abstract. The aim of the study is to analyze the influence of irrigation regime on evapotranspiration (ET) of sunflower, in terms of total and average daily values, its effectiveness in terms of yield, and the peculiarities of its formation. The field experiment was conducted in the region of Plovdiv, with hybrid PR-64-E-83. The variants of the study are: without irrigation, optimal irrigation with initial humidity at 75% of FC for the layer 0–80 cm and irrigation with 50% and 150 % of irrigation rate, respectively. Seasonal evapotranspiration of sunflower varies from 274 to 342 mm. Irrigation with 50% of the optimal irrigation depth causes ET increasing with an average of 33.1% (from 26.1 to 37.4%). The optimally irrigated sunflower uses from 475 to 559 mm. Increase of ET as compared with the rainfed sunflower is an average of 67%. In case of irrigation with 150% of the irrigation depth ET increases with extra 2.5 – 26.7% (an average of 13.5%). ET of sunflower was formed in the following way for the conditions of the experiment: In rain-fed conditions rainfalls share 49 – 82% and water supply – from 18 to 51% of ET. By irrigation with 50% of rate the sharing of rainfalls is 36-64%, for water supply is 17-33% and irrigation depth – 14-31%. By optimum irrigation sharing is respectively 28-56%, 16-23% and 25-49%. The maximum value of daily ET for rainfed sunflower varying from 3.3 to 5.6 mm. Irrigation with norm of 50% increases values of ET to 5.2 – 6.1 mm. The maximal value of this regime of irrigation is most often in the flowering period. In case of optimal irrigation the maximal values of daily ET will remain the same usually to the beginning of phase „seeds fill”, and the values are between 6 and 7 mm.