How does irrigation lead to salt buildup in Indus River soils?

In the Indus River basin, salt buildup in soils is primarily a consequence of canal irrigation that lacks adequate drainage systems. This process, known as secondary salinization, occurs through two main mechanisms:12

• Waterlogging: Water from unlined irrigation canals seeps into the ground, causing the water table to rise. When the groundwater reaches or nears the surface, it can form shallow lakes or saturate the soil, rendering it useless for cultivation.1
• Evaporation: In the intense heat of the region, water that has risen to the surface—or water applied during irrigation—evaporates, leaving behind the dissolved salts it carried. Because irrigation water always contains some level of salt, and plants typically exclude these salts while absorbing water, the residual salt accumulates in the soil profile over time.134

Without proper drainage to flush these salts downward using excess water, the concentration of salt eventually inhibits plant growth. While the government has attempted to mitigate these issues through projects like the Left Bank Outfall Drain, improper design has in some instances exacerbated environmental damage.3415