Használt termálvíz mezőgazdasági elhelyezésének (öntözés) hatása a talaj kicserélhető nátrium tartalmára és az összes oldott sótartalmára | Effect of irrigation with used geothermal water on the sodicity and salinity of agricultural soil

Because of the increasing frequency of extreme hydrological events in Hungary, conventional agricultural practices need to be modified in order to adapt to changing environmental factors. The development of new irrigation management practices, the use of water- and energy-saving methods and the reutilization of wastewater (agricultural effluents, treated wastewater, etc.) could be important elements in this adaptation. Used geothermal water (so called effluent water) from an intensive African catfish farm, water from the River Körös and improved effluent water were used in a lysimeter experiment for the irrigation of energy willow. The experiments were conducted at the Research Department of Irrigation and Water Management (OVKI) of the National Agricultural Research and Innovation Centre (NAIK) in Szarvas, Hungary. Seven irrigation treatments and one rain-fed control were applied in four replications during the 2015 vegetation period. The results demonstrated that the use of effluent water is limited by high values of the chemical properties responsible for sodification (EC, SAR, sodium content and bicarbonate toxicity,). For this reason, an improved form of effluent water produced by dilution and the addition of gypsum was also used for irrigation. Tests on changes in the exchangeable cation content of the soil showed that irrigation with effluent water led to the accumulation of exchangeable sodium at all the irrigation rates, while no significant changes were observed for any exchangeable cations in the case of diluted, treated effluent water. When water from the River Körös was used for irrigation no change in this parameter was recorded at irrigation rates of 15 or 30 mm, but the 60 mm irrigation rate resulted in a significant decline in the sodium content, associated with leaching. In the non-irrigated treatment a decrease in the exchangeable calcium content was accompanied by an increase in the quantity of magnesium on the surface of soil colloids, which could probably be attributed to natural sodification processes. After a year of irrigation with effluent water (at the 60 mm irrigation rate) the total dissolved salt content of the soil at a depth of 0-40 cm differed significantly from the values recorded in treatments given river water, but when the diluted, treated effluent water was applied, the total dissolved salt content in the soil was similar to that in the river water treatment and did not exceed 0.05%. Further soil analyses will be required to gain a better understanding of the effect of these irrigation sources on the soil, and the experiment will be continued for several years to give a long-term picture. It is clear from the present results, however, that effluent water from the intensive African catfish farm can safely be used for irrigation in a sustainable manner after mixing with good quality water and the addition of gypsum, without the danger of sodification or salt accumulation.