How does over-irrigation lead to salinization?
Over-irrigation actually can increase soil salinity due to the transport of dissolved salts.
Irrigation salinity occurs due to increased rates of leakage and groundwater recharge causing the watertable to rise. Rising watertables can bring salts into the plant root zone which affects both plant growth and soil structure. The salt remains behind
in the soil when water is taken up by plants or lost to evaporation.