# Effects of Irrigation with Desalinated Water on Lettuce Grown under Greenhouse in South Korea
## 2 Materials and Methods  
### Experimental Design  
The experiment was conducted in a greenhouse at the Pyeongchang Campus, Seoul National University, which is located in Gangwon-do, South Korea (37\({}^{\circ}\)32\({}^{\prime}\)51\({}^{\prime\prime}\) N and 128\({}^{\circ}\)26\({}^{\prime}\)26\({}^{\prime\prime}\) E). Eight experimental plots (22 m length \(\times\) 0.4 m width \(\times\) 0.4 m height) were designed for both saline and desalinated water irrigation experiments in a randomized complete block with four treatments and two replications. Plots were filled with commercial soil (Seoul Bio Inc, Chungcheongbuk-do, Korea). Characteristics of the soil were as follows: loam texture (49.6% sand, 33.8% silt, and 16.6% clay); pH measured in 1:5 soil:water suspension, 5.6; electrical conductivity of the saturated-soil extract (EC\({}_{e}\)), 8.5 dS m\({}^{-1}\); cation exchange capacity (CEC), 73.2 cmol kg\({}^{-1}\); total nitrogen (T-N), 0.596%; total phosphorus (T-P), 1676.0 mg kg\({}^{-1}\); organic matter (OM), 65.5%; phosphorus pentoxide (P\({}_{2}\)O\({}_{5}\)), 1521.5 mg kg\({}^{-1}\); calcium (Ca\({}^{2+}\)), 4534.8 mg kg\({}^{-1}\); magnesium (Mg\({}^{2+}\)), 1935.5 mg kg\({}^{-1}\); sodium (Na\({}^{+}\)), 1042.1 mg kg\({}^{-1}\); and potassium (K\({}^{+}\)), 5478.8 mg kg\({}^{-1}\)[15]. Drip irrigation was employed and one drip irrigation lateral was placed on the soil surface in the center of each plot. Irrigation water for each treatment was stored in 100 L plastic containers and was supplied using a metering pump (50 mL per minute) for each treatment. Lettuce (_Lactuca sativa_ L.) is one of the most common vegetable crops grown in greenhouses from South Korea [6]. The lettuce cultivar used for both experiments was 'Sunpungpochodp'. One-month-old lettuce seedlings were transplanted in rows with 30 cm spacing along the drip lateral in each plot. The planting and harvest dates for each experiment are shown in Table 1. Daily temperature and relative humidity in the greenhouse were monitored during the experimental period. To investigate the effects of irrigation with saline water on lettuce growth and yield, four different levels of saline water were prepared. Tap water was used as a control (BS#01). Saline irrigation water with three salinity levels was prepared by adding sodium chloride (NaCl) to tap water. The salinity levels of irrigation water (EC\({}_{\text{w}}\)) for the three treatments (BS#02, BS#03, and BS#04) were based on the salinity threshold for irrigation water given by [PERSON] [16]. The target EC\({}_{\text{w}}\) values were 0.9, 2.1, and 3.4 dS m\({}^{-1}\) for BS#02, BS#03, and BS#04, respectively. The small-scale brackish water desalination (BWD) system (Blue BS Inc., Suwon, Korea) with a capacity of 10 m\({}^{3}\) day\({}^{-1}\) was installed and operated in order to conduct the experiment with desalinated water (Figure 1). The BWD system consists of a micro-bubble generator, zeta potential floating tower, microfiltration (MF) membranes, reverse osmosis (RO) membranes, and several pumps. The feed water at three different salinity levels (0.9, 2.1, and 3.4 dS m\({}^{-1}\)) was prepared using the same procedure as described above and was then desalinated by using the BWD system. This desalinated water was subsequently used as irrigation water for the second experiment (AS#02, AS#03, and AS#04). Tap water was used as a control treatment (AS#01). None of the applied water leached from the plots, and fertilizer was not applied to any of the treatments. In order to investigate the effects of continued irrigation with saline and desalinated water on crop yield and soil quality, the soil in each plot was not changed after completing the first phase of each experiment. After finishing the experiment with saline irrigation water, however, all plots were newly filled with commercial soil before starting the experiment with desalinated irrigation water.