@ARTICLE{Mladenova_Bojidara_Impact_2007,
 author={Mladenova, Bojidara and Varlev, Ivan},
 number={No 11},
 pages={71-77},
 journal={Journal of Water and Land Development},
 howpublished={online},
 year={2007},
 publisher={Polish Academy of Sciences; Institute of Technology and Life Sciences - National Research Institute},
 abstract={The relative relationships “yield – evapotranspiration” were used long time ago. The well known linear relationship yi = 1 – ky (1 – ei), where yi is relative yield, ky – yield response factor and ei – relative evapotranspiration was proposed. It’s usually assumed that ky is constant for a given crop and climatic conditions. It was found, however, that ky for late variety of maize H 708 varied through the study years (1984–1990) in the Plovdiv region (South Bulgaria, altitude 150 m). During the dry years it was significantly higher than in the medium and humid years. The range of ky for maize in this location was 1.12–1.90, the average value being 1.50. The climate in the Sofia region (the ex-perimental field of Chelopechene, altitude 550 m) is comparatively more humid. The two regions approximately outlined the boundaries of the appropriate economical conditions for grain maize pro-duction. The experiments in the Sofia region were carried out in the years 1994–2000. The seven years results for mean variety maize showed that the relationships “yield – evapotranspiration” and, respectively, ky varied at these climatic conditions too. The highest ky value was 1.41 for the driest year (2000) and the lowest value – 1.05 for the most wet years (1995, 1999). The value of ky for av-erage years was 1.21. The yield response factor ky is of more significance when the relative evapotranspiration is less than 0.7–0.8. Thus, the extreme or the average values of ky could be used for the corresponding climatic regions. The relationships between ky and relative yield were estab-lished without considering irrigation.},
 type={Article},
 title={Impact of extreme climate years on relative “yield – evapotranspiration” relationships},
 URL={http://ochroma.man.poznan.pl/Content/116961/PDF-MASTER/%5B20834535%20-%20Journal%20of%20Water%20and%20Land%20Development%5D%20Impact%20of%20extreme%20climate%20years%20on%20relative%20yield%20-%20evapotranspiration%20relationships.pdf},
 doi={10.24425/jwld.2007.133851},
 keywords={climate, evapotranspiration, maize, yield, yield response factor},
}