In order to calculate water deficit of agricultural crops, it is necessary to
have an insight into the evapotranspiration process. As for evaluation of
reference evapotranspiration, the Penman-Monteith (FAO56-PM) method,
suggested by The International Commission on Irrigation and Drainage (ICID)
and Food and Agriculture Organization of the United Nations (FAO), requires
several climate parameters, which are often unavailable. Thus, in this
paper, the methods for computing ETo, which use limited weather data, were
tested and then compared to FAO56-PM. The selected methods were those most
often used as the replacement for FAO56-PM: Hargreaves, adjusted Hargreaves,
Copais, Turc, Priestley-Taylor, Makkink and Hamon. ETo was calculated at the
daily and average monthly levels, for the 2010-2013 period, using data from
the following meteorological stations: Nis, Belgrade, Novi Sad, Loznica,
Valjevo, Zlatibor, Cuprija and Kikinda. Special importance was given to the
vegetation period during the dry season due to the application of
irrigation. The comparison of methods was based on statistical analysis,
using parameters: MXE, MAE, RMSD, ARMSD, WRMSD, b and R2. The highest rate
of matching FAO-PM at the average monthly level, as well as during the 2012
growing season, was shown by Copais, Turc and Priestley-Taylor methods, thus
these methods may be recommended as the replacement for FAOPM under climate
conditions of Serbia. In case only temperature data are available, the
results of this research justify the use of the adjusted Hargreaves equation
to calculate ETo for the vegetation period.