The salt tolerance of a plant can be evaluated by observing changes in plant growth in saline conditions compared with control conditions, with salt-sensitive plants having a greater reduction in growth compared with salt-tolerant plants (Munns, 2022). In addition to the reported plant salt tolerance, growth responses depend on the severity of salt stress (the concentration of salt in the soil solution) and the duration of exposure of the plant roots to salt (Hasegawa et al., 2000; Munns and Tester, 2008; Zhu, 2003).
When salts accumulate in the growing substrate under normal irrigation, this can increase substrate salinity levels. One method of correcting higher substrate salinity levels involves increasing the volume of water applied at each irrigation event (Petersen, 1996). The increased amount of water leaches the salts in the substrate and decreases salinity levels (Petersen, 1996). By measuring the amount of water that drains as a function of the amount of water applied, we can calculate the leaching fraction (LF). Growers can use the following salt balance equation: LF = ECw/5(ECe−ECw), where ECw is the electrical conductivity (EC) of the water source and ECe is the desired EC for the substrate to determine the leaching requirement (Petersen, 1996). The leaching requirement is the minimum LF for maintaining a desired EC in the substrate. It is possible to input the EC of any water source into this equation and determine the appropriate leaching requirement (how much water to apply to get a desired amount to drain) to maintain a predetermined substrate EC for that crop. This has potential benefits when using either reclaimed wastewater (RWW) or source water with high salt levels, both of which can have high EC.
We wanted to test this equation to determine if we could maintain desirable substrate EC levels when using irrigation water with high salt concentrations either from saltwater or from RWW. In our first experiment, we compared the growth of ‘Hope’ philodendron (Philodendron selloum) and ‘Tineke’ ficus (Ficus elastica) with tap water and two sources of RWW. In our second experiment, we compared the growth of ‘Looking Glass’ begonia (Begonia fibrous), ‘Freddie’ calathea (Calthea concinna), and ‘Déjà vu’ philodendron (Philodendron selloum) watered with tap water and saltwater. Plants used in both experiments were considered have low to moderate salt tolerance (Broschat and Meerow, 1991).
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