When evaporation from the soil surface and
transpiration from plants exceeds water input, salts can start to accumulate at
the soil surface. This is because when water from the soil surface evaporates,
it wicks salts that are suspended in the soil solution to the soil
surface. This is particularly a problem in high-tunnels that are in
production year-round. Accumulating salts are not just sodium (Na+) and chloride (Cl-) ions, but are also essential plant nutrients... calcium (Ca2+), magnesium (Mg2+), potassium (K+), ammonium (NH4+), hydrogen (H+), phosphate (HPO42-), sulfate (SO42-), and nitrate (NO3-) are all salts. Nitrate accumulation is particularly frequent in high tunnels as high-value crops are well fertilized, and since there is no rainfall to leach the nutrients, they accumulate year after year.
To learn more about soil salinity, how it happens, and what you can do about it, please read Perennia’s factsheet: http://www.perennia.ca/wp-content/uploads/2015/12/Soil-Salinity-NS-Hi-Tunnels.pdf
