Parameters of the Evapotranspiration-Yield Relationship in a Grass Mixture of English Ryegrass and Red Fescue

Abstract

The study aims to establish the parameters of the relationship “Cumulative Evapotranspiration (ET) - yield from aboveground biomass” in a grass mixture of English ryegrass (Lolium perenne L.) and Red fescue (Festuca rubra L.). The results are necessary for the needs of landscaping in urbanized areas. Data from an experiment with the application of a regulated water deficit, carried out in the period 2009-2011 at the University of Forestry - Sofia on anthropogenic bulk soil, were used. Data on relative ET and relative yield were processed by the method of least squares, using three types of formulas - linear (FAO), power, and two-power. The most accurate is the two-power formula, which describes the dependence through an S-shaped curve at (raport of correlation) R=0.989. It has the following form: Y=[1–(1–x)1.74]5.29, where Y is the relative yield at the corresponding ET, which is denoted by x. High accuracy also shows the power formula, which has the following form: Y=1–2.23(1–x)1.28 and R=0.976. The FAO linear formula represents the relationship at R=0.805. It has the following form: Y=1–1.62(1–x).