17: Soil Salinity and Sodicity

Question 1

Soil salinity

Answer 1

Accumulation of base cations and anions (Ca, Mg, Na) with chloride and salts (sulfate, bicarbonate) to a point where plant growth and soil function are damaged

Question 2

Soil sodicity

Answer 2

An excess of sodium (Na+) in soil

Question 3

Natural causes of soil salinity

Answer 3

Parent material
Groundwater
Low rainfall
High temperature

Question 4

Human-induced causes of soil salinity

Answer 4

Fertilizer management
Irrigation management

Question 5

Parent material effect on soil salinity

Answer 5

Slowly releases cations and anions into water

A natural cause of soil salinity

Question 6

Groundwater effect on soil salinity

Answer 6

Movement of water table up also moves salts up, then when it moves back down the salts are left there

Sources of salts:
- Weathering
- Fossil salt deposits
- Proximity to seawater

A natural cause of soil salinity

Question 7

Low rainfall and high temperature effect on soil salinity

Answer 7

low rainfall + high temps = high evapotranspiration rates and no leaching

A natural cause of soil salinity

Question 8

Fertilizer and irrigation management effect on soil salinity

Answer 8

All water has some dissolved salts, and this can accumulate over time. Salt accumulates in areas with high evapotranspiration and is exacerbated by fertilizer application

Question 9

How does a high salt concentration affect a plant’s ability to draw water from soils?

Answer 9

High salt concentration in soil decreases water potential, which means plants need more energy to draw water from the soil.

Question 10

Typical salinity symptoms

Answer 10

Reduced water and nutrient uptake
Stunted growth
Yellowed leaves
Old leaves accumulate salts and drop off
Specific ion toxicity: Na, Cl, and B

Question 11

How does the size of cations affect colloid cohesion?

Answer 11

Divalent cations (like Ca2+) have smaller hydration spheres and fewer cohere to colloids, so these colloids can clump together (flocculate)

However, monovalent cations (like Na+) have larger hydration spheres AND are more abundant which keeps colloids from clumping together

Question 12

Consequences of soil salinity on soil and plants

Answer 12

Massive structure and loss of porosity
Decreased infiltration and increased runoff - higher risk of erosion
Decreased seedling emergence/root growth

Question 13

How to determine if a soil has salinity/sodicity issues?

Answer 13

1. Observe plant growth
2. Surface salinity and sodicity
3. Subsurface sodicity
   - Columnar structure
   - Gives the soil an almost rubbery consistency when wet

Question 14

Reclaiming saline soils

Answer 14

Reduce salt input
Leach out salts (need enough water)
Drain away the leachate
Have a readily available and acceptable sink for the drain water
Select salt-tolerant plants