CROP RELATIONSHIP "YIELD - EVAPOTRANSPIRATION" FOR COMMON BEAN

The aim of the study is the crop relation "Yield-Evapotranspiration" (ET) for common beans, based on data obtained by full irrigation and irrigation with reduced irrigation rates. The experiment conducted in the experimental field of Agricultural University of Plovdiv with "Dobrudzhanski 7" variety in the period 2014-2016. The relationship has been studied in two directions - with regard to the summary ET and in terms of ET by phases. Thus the vegetation period of the beans is divided according to the following phases: I - growth, II - flowering, III - productive (pod development and grain filling) and IV - maturing. In both cases, existing formulas (linear, power and multi-power) were used, where the experimental data was processed by the smallest squares method. The relationship ''Yield-Seasonal ET'' is best represented by two-power formula: Delta Y = [1-(1-Delta ET)(N)](M). The graph is expressed graphically by the S-curve and R = 0.986 (N = 2.3 and M = 9.1). The crop relationship "Yield-ET by phases" is best expressed by the two-power formula at R = 0.921. The power of the whole vegetation period is N=1.3 and in phases is: m(1) = 0.05, m(2) = 0.79, m(3) = 0.49 and m(4) = 0.28. This means that the second sub-period is the most sensitive. The first period has very little sensitivity and the third and fourth periods are intermediate.