This study was conducted to investigate the effects of low salinity stress on growth, yield, water use efficiency (WUE), and fruit quality of cherry tomatoes cultivated under a soilless condition. The experiment was conducted using Hydroponic Power's Pot under six salinity levels (electrical conductivity (EC): 0.78, 0.91, 1.10, 1.26, 1.41, and 1.58 dS m-1), with three pots (six plants) in a completely randomized design in each treatment. The results showed that plant fresh weight, soil-plant analysis development (SPAD) value (leaf chlorophyll), and dry weight were significantly affected by salinity stress at EC = 1.58 dS m-1. Tomato yield was significantly affected by salinity stress when EC reached 1.41 dS m-1, and was more sensitive than growth variables. Fruit quality was improved with increasing salinity. Evapotranspiration was also significantly affected by salinity stress at EC = 1.58 dS m-1. However, WUE for yield (fresh fruit) and biomass were not significantly different among salinity levels. The SPAD value (leaf chlorophyll) was the most sensitive indicator for salinity stress. The salinity threshold of the tomatoes was 1.41 dS m-1 to achieve higher fruit quality and yield by using Vegetable Life A nutrient solution.
This study aims at establishing a groundwater model for the 100-meter aquifer of a coastal area of the Mekong Delta, and applying it to simulation of the groundwater heads under possible changes in rainfall and groundwater management in the future. The model, iMOD, was calibrated using historical data of groundwater level and model input requirements. It was confirmed that the calibrated model could work properly to reproduce the distribution of the groundwater table and its response. For scenario setting, several cases of future rainfall conditions for the period from 2015 to 2035 were set up based on the downscaled output from the global climate model with bias correction. For each of the combinations of climatic conditions and pumpage, model simulation was carried out to estimate groundwater tables. The results showed: (1) If the groundwater pumping stays at the same level as present, groundwater heads can maintain the present level under increased recharge from the future rainfall, whereas slight decline in groundwater heads would continue under the current rainfall; (2) If the groundwater pumping increases along with increasing water demand, significant consecutive drawdown of groundwater tables will happen. Particularly when considering some reduction in recharge due to rainfall loss and uncertainty of rainfall, groundwater depletion might be more serious; (3) Reduction in pumping rate was found to contribute much for recovery of groundwater.