Introduction: Evapotranspiration systems (ETS) are among the cleaning plants for treatment and disposal of municipal wastewater, where all wastewater is used to grow plants such as willows. In the ETS, the concentration of salt (NaCl) eventually increases, which has an impact on the efficiency of wastewater treatment and the growth of willow trees. Purpose: With the help of pot experiment, we wanted to determine the impact of different concentrations of NaCl on growth and evapotranspiration of willows in the ETS and compare responses of salinity of 3 different clones of willow trees. Working methods: The pot experiment took place in the greenhouse on 3 clones of White Willow (Salix alba) in the 5 test portions and control batch without NaCl (a total of 90 samples). We tested the following concentrations of NaCl: 0.1 g/L; 0.2 g/L; 0.5 g/L and 1.0 g/L. We took notes of daily water usage and statistically processed the data with a computer, using Microsoft Excel 2010, where we tried to figure out the differences by analysis of variance (ANOVA). With the computer program SPSS 17.0, we used t-test for determination of difference characteristics and Pearson's correlation coefficient for analysis of connectedness. We calculated the level of normalized relative transpiration (the NRT) from absolute water consumption. At the end of the experiment, we measured height, thickness of the shoots and counted the number of shoots and made a graphic comparison between them. The results: The clone V160 used most of water with all concentrations of NaCl. In clone V093, NRT was the highest with the NaCl concentration of 1.0 g/L, in clone V160 at concentration 0,2 and 0.5 g/L, and in clone V052 at concentration 0.5 g/L. In clone V052, at NaCl concentration of 0.2 g/L, NRT was less than 100% from the beginning of the experiment. Discussion and conclusion: In our experiment, NaCl did not pile up in the ground to such extent that it would slow down the transpiration and affect the growth of willow trees. Based on the obtained results, we can expect that in S. alba clones V093, V160 and V052 it would not come to effects of NaCl on the efficiency of treatment of urban wastewater in real ETS at a concentration of NaCl up to 1.0 g/L in 1 vegetative period. We assume that the results in real ETS could differ from ours, because we did not use wastewater that could boost the uptake of water and speed up the accumulation of NaCl. In addition, it would make sense to monitor the response of willow trees and the interaction of various factors on the growth of willow trees during more vegetative periods.
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