How does flushing soil with fresh water remove salts from farmland?

Flushing salt-affected farmland with fresh water is a process known as leaching, which is essential for restoring soil productivity in areas where salts have accumulated due to irrigation or poor drainage.12

The process works through the following steps:

• Improving Drainage: Before flushing, the soil must have adequate drainage. This ensures that water can move downward through the soil profile rather than stagnating or moving upward toward the surface via groundwater.1
• Leaching: Fresh, nonsaline water is applied to the soil surface. As this water percolates downward, it dissolves the accumulated salts—such as chlorides, carbonates, and sulfates—that are present in the soil.1
• Removal: The dissolved salts are carried away from the root zone by the downward-moving water and are eventually removed from the area through drainage systems.12

In cases of "sodic soils," where sodium ions have become adsorbed to clay particles, simple flushing is often combined with chemical amendments like gypsum. These amendments provide calcium to replace the sodium, allowing the sodium to be leached out of the soil profile effectively.1