What are the theoretical and actual (measured) minimum water potentials in plants?
Sodium Chloride (which I am here assuming to be the major salt in your solution) has a solubility of 6 Moles/L this corresponds to 12000 mOsmol, so the 2000 mOsmol you are measuring is not entirely implausible. However normally plant cells should have an osmolarity on the order of 300-400 mOsmol. In order to judge if your value was calculated correctly, it would be necessary for you to tell us exactly how you calculated and how you measured.
I am not aware of such literature but I am not a plant physiologist myself.