Drip irrigation can lead to localized increases in soil salinity due to the way water and salts move within the soil profile. The salt accumulation is not uniform across the wetted area.
Here's a breakdown of the process:
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Water Application and Evaporation: Drip irrigation delivers water slowly and directly to the root zone. This targeted application minimizes water loss due to surface evaporation. However, evaporation still occurs at the soil surface near the dripper.
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Salt Concentration and Movement: As water evaporates from the soil surface, the dissolved salts in the irrigation water or already present in the soil are left behind. This leads to a concentration of salts at the soil surface and the periphery of the wetted zone.
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Wetted Pattern and Salt Distribution: The wetted pattern created by drip irrigation is not uniformly saturated. Water moves outwards from the emitter via capillary action. Salts are carried along with this water movement. Because water is preferentially drawn upwards by evaporation, salts tend to accumulate at the surface and at the edges of the wetted zone, further from the emitter itself. The reference indicates that soil salinity increases with distance from the emitter.
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Subsurface Drip Irrigation: With subsurface drip irrigation (SDI), the driplines are buried. In this case, water still moves upward from the dripline via capillary action, and evaporation at the surface pulls salts upwards, leading to salt accumulation above the drip lines.
In summary, drip irrigation concentrates salts through the following mechanisms:
- Evaporation: Water evaporates from the soil surface, leaving behind dissolved salts.
- Capillary Action: Water moves outwards from the emitter, carrying salts with it, and then upwards towards the surface via evaporation, leading to accumulation.
- Localized Application: Salts concentrate in the wetted zone created by the drip emitters, specifically at the periphery and surface.
