# Effects of Irrigation with Desalinated Water on Lettuce Grown under Greenhouse in South Korea
## 1 Introduction  
Farmers increasingly consider desalinated water as a competitive source of irrigation water, particularly for high-value cash crops like greenhouse vegetables and flowers [1; 2]. Due to enhanced desalination techniques and reduced costs [3; 4; 5], desalination has become a viable option for greenhouse cultivation. Desalinated water allows farmers to produce salt-sensitive and often more profitable crops [2], as well as provides quality irrigation water to greenhouse cultivation areas that suffer from freshwater scarcity but are rich in brackish water resources.  
South Korea has about 93,551 ha devoted to greenhouse cultivation [6], most of which are located in the estuary and coastal area in order to easily supply irrigation water, mainly from groundwater extraction. Along with increased drought frequency [7], anthropogenic activities, including extensive groundwater extraction and upstream dam construction, have resulted in the salinization of both groundwater and estuarine surface water. Due to the use of saline water for irrigation, with the subsequent restriction in plant physiological activity [4; 8; 9], farmers have increasingly reported salt damages in greenhouse cultivation in recent years. Furthermore, salinization limits crop species withincoastal greenhouse areas. However, desalination of brackish water could likely overcome salinity problems in coastal areas and produce quality irrigation water.  
Although the desalination process reduces undesirable salts in saline water, ions including the essential nutrients required for crop growth like calcium (Ca\({}^{2+}\)), magnesium (Mg\({}^{2+}\)), and sulfate (SO\({}_{4}\)\({}^{2}\)) can also be removed [5; 8]. Irrigation with desalinated water that lacks essential nutrients can negatively affect crop productivity. As a matter of fact, Mg\({}^{2+}\) deficiency symptoms were observed in crop productions (e.g., basil, tomatoes, and flowers) when farmers used desalinated water for irrigation in Israel, thus requiring additional fertilization [5]. In addition, the effects of irrigation with desalinated water on soil-water-plant relations can vary depending on the desalination system and the agricultural environment, which includes the quality of feed water, target crops, soil and weather conditions, and agricultural practices including irrigation methods. Therefore, before introducing a desalination system, it is necessary to evaluate its potential effects on a local agricultural environment. Many studies have been conducted to assess impacts of irrigation with seawater [10; 11] as well as wastewater [12; 13] or reclaimed water [14]. However, relatively few studies [1; 4] have been undertaken to evaluate the impacts of irrigation with desalinated water on crop growth and soil properties.  
In this study, we assessed the effects of desalinated water irrigation on lettuce (_Lactuca sativa_ L.) cultivation within a greenhouse in South Korea. To do this, a newly developed small-scale brackish water desalination (BWD) system described in the following section was employed to produce desalinated irrigation water. Tap water (control) and three waters with different saline concentrations were used to irrigate eight experimental plots, resulting in four treatments and two replications for the experiment with saline irrigation water. Tap water as control and desalinated water from the three saline concentrations used in the former trial, processed through the desalination system, were utilized in the experiment with desalinated irrigation water. The chemical properties of soil and irrigation water, and the ways in which the lettuce crop responded to the treatment (i.e., leaf number, length, and width, shoot and plant weights, and sodium accumulation) were analyzed.