Question

Soil salinity increase or decrease the ph of soil?

Answer 1

I guess that base saturation is close to 100% in Ali's soil and if pH really dropped from 8 to 7.6 it seems unlikely to me that other buffer mechanisms than carbonates are involved. By using NaCl solution Ali exchanged Ca (and likely Mg) by Na, which should not alter pH, since NaCl and CaCl2 (MgCl2) are neutral salts.But maybe the observed drop in pH is an effect of high Na concentrations on the pH electrode? I am aware that typically this Na-effect occurs at higher pH values, but anyway I would recommend to check this, for example by adding NaCl to the pH calibration buffers. Just to make sure it is not an electrode problem.