The problem of high soluble salts in high tunnels
"However, another scenario that I think is happening a great deal more often in our high tunnels is when plant roots absorb the excess salts in the soil and are unable to metabolize them. The soluble salts enter the roots and are moved through the water conducting tubes to the leaves where the water evapotranspirates, gradually concentrating the salts to toxic levels. The consequence of this type of salt stress in plants is a myriad of problems such as: poor growth, thin canopy, excessive leaf drop, poor fruit set and poor yields with the next damage level up being brown or necrotic leaf edges especially on older leaves that can curl (Fig. 1)."
Figure 1. Soluble salt damage to peppers in a high tunnel
"Some of the practices that can exacerbate the salt problem include: allowing the soil to become too dry for even a short time, frequent brief irrigations, short crop rotations, shallow or minimum tillage and little if any soil flooding. Some of our vegetable crops are much more sensitive to high soluble salts than others. Crops such as green beans, onions and peas are most sensitive while cabbage, cucumbers, peppers and potatoes are a little salt tolerant and broccoli, squash and tomato are moderately salt tolerant. These differing sensitivities may be why if tomatoes are grown most often in the HT and then peppers or cucumbers are grown the soluble salt problem can ‘suddenly’ appear."
"Some of the possible in-season remedies for high salts include stopping the use of all fertilizers until salt concentrations return to acceptable levels, having adequate drainage to help move salts out of the root zone and flushing the soil with as much water as possible for several days (water should be applied slowly so it seeps down into the soil and does not runoff). After the season it may be best to take the plastic off of the HT and allow rain and snow to move the salts out of the growing zone."
Source: University of Delaware