Parameters of “yield-irrigation depth” relationship for sunflower grown in the region of Plovdiv

A. Matev, R. Petrova
Abstract. The aim of this work is to establish parameters of relationship “yield-irrigation depth” for sunflower (grown in the region of Plovdiv), using different equations, as follows: y = ax2 + bx + c; y = y + 2 (1–y ) x – (1–y )x2; Y = 1 – (1 –Y )(1 – x)n. The source data used for the study are from a field experiment, carried 0 0 0 0 out in the region of Plovdiv (Bulgaria) on alluvial-meadow soil, with sunflower hybrid “PR-64-E-83”. Variants of the field experiment are: 1 – without irrigation; 2, 3 and 4 – irrigation with 50, 100 and 150% of the irrigation rate, determined by optimal variant (pre irrigation soil moisture 75% of FC for the layer 0 – 80 cm). With irrigation of 150% the irrigation depth moistens the layer 0 – 100 cm. If the maximum value of relative irrigation depth is 1.000, the relative irrigation depth of the other variants is: variant 1 – 0.000, variant 2 – 0.333 and variant 3 – 0.667. The results show that equation /3/ is the most suitable from a mathematical point of view and at the same time corresponding well with the biology of the crop. Variations of calculated yields using this equation to experimental yields are from – 1.6 to + 6.2%. The following parameters are established: n = 3.37 (from 2.34 to 4.67) and R = 0.997 (from 0.986 to 1.000). The representative type of equation /1/ is: Y = 0.586+1.136x–0.726×2 by R2 = 1. Variations of calculated yields using this equation to experimental yields are from – 2.2 to + 9.1%. Under the conditions of this work we calculated yield by a second degree equation: y = y + 2(1 – y )x–(1–y )x2 is always smaller than the experimental with variation from 0 0 0 0 to 16.3% and R=0.974. All established parameters of the relationship “yield – irrigation depth” in this paper are valid by variants with reduction of the irrigation rate compared to that calculated for wetting the layer 0 – 100 cm and when irrigations were scheduled by pre irrigation soil moisture 75% of FC for the soil layer 0 to 80 cm.

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