Soluble Salts & Plant Growth

2. Soluble Salts & Plant Growth
Excess salt kills growing plants
High salt levels can render a soil
unproductive for decades, centuries
 Soluble Salts
 Not restricted to table salt – many
different salts can be formed due to
chemicals available
 In some soils, salt concentrations higher
than seawtaer (>3-4% total salt)

3. Soluble Salts & Plant Growth
 Irrigation can speed a soil salt problem:
 All irrigation water contains salt
 If a farmer adds 4” of water w/ 1000mg salt/L adds
890 lb/ac salt/yr
 Raises naturally salty groundwater level
closer to surface
 Groundwater can rise to surface through capillary
action & evaporate – leaving salt behind

4. Soluble Salts & Plant Growth
 Measuring Soluble Salts
 Electrical Conductivity (EC) – conductivity
directly proportional to salt concentration
 Higher EC reading = more electricity
conducted = higher soil salinity
 Effects of Salt Concentration
 Usually, just reduce plant growth due to
osmotic effect – interferes w/ plant’s
ability to extract soil water
 High saline soils can actually rod water back
from plant roots

5. Soluble Salts & Plant Growth
 Plants have varying tolerance to soil salts
 Not all affected at same time/same way
 Effects of Specific Ions
 Na & Cl can be toxic to woody
ornamentals & fruit crops
 Some plants can be injured by <5%
exchangeable Na for some fruits, other
woody ornamentals <.5% Cl & .25% Na

6. Soluble Salts & Plant Growth
 Salt-Affected Soil Classification
 Saline Soils
 Enough salt at some position w/in the root
zone to interfere w/ plant growth
 Causes:
 Unleached products
 Salty irrigation water
 Upward movement of groundwater

7. Soluble Salts & Plant Growth
 Sodic Soils
 Salt imbalance caused by Na is the dominant
cation, rather than Ca
 Water infiltration problems
 Toxic levels of Na
 pH >8.5
 Causes:
 Irrigation water
 Weathering of parent materials
 Upward migration of salty groundwater
 Contamination from oil/gas well production

8. Soluble Salts & Plant Growth
 Can have a sodic horizon
 Saline-Sodic Soils
 High in salinity & high in Na
 Affect plants by osmotic effect & toxicity of Na
 Good water infiltration
 pH <8.5
 Attempts to improve condition by leaching
results in sodic soil

9. Salt Balance
 23% of world’s cultivated land saline
 39% sodic
 Australia – many soil salinity problems
 Irrigation & land clearing – primary
causes
 Salt buildup existing/potential hazard
on 42m ac of irrigated land in U.S.

10. Salt Balance
 Salt balance – outgoing salt =
incoming salt
 Managed leaching to help wash away
any salt buildups
 May call for a leaching requirement to
remedy & keep crops productive

11. Reclaiming Salty Soils
3 Rules:
1. Establish internal drainage
 If not already adequate
 May require tile installation, ditching
 Can be impractical/costly
1. Replace excess exchangeable Na
 Necessary for sodic & saline-sodic soils
 Extent varies w/ soil texture, clay, quality of available
water extent of damage
1. Leach out most of soluble salts
 Especially in root zone
 Use good quality irrigation water

12. Reclaiming Salty Soils
 Reclaiming Saline Soils
 Can be easy, if:
 Low-salt irrigation water is available
 Internal & surface drainage is adequate
 Disposal areas for salt available
 Difficult when:
 High water table
 Fine-textured soils

13. Reclaiming Salty Soils
 Add organic mulch – slows movement of
water to the soil surface
 Quantity of water required to help leach:
 Depends on depth needed to leach
 % of salts to be removed
 How its done (constant/intermittent sprinkling)

14. Reclaiming Salty Soils
 Reclaiming Sodic & Saline-Sodic Soils
 Sodic soils
 Downward movement of water can’t leach out
excess Na
 Must first replace Na on CEC sites
 Use gypsum
 Can then leach out excess Na
 Can also use S to reduce soil pH

15. Managing Salty Soils
 Water Control
 Maintain high water content in soil
 Keeps salts diluted
 Plants more able to tolerate higher salt levels
 Leach soil before planting to move salts
below root zone in early plant
development

16. Managing Salty Soils
 Planting Position
 Salt moves w/ water
 Plant on side of ridges where salt build-
up may be avoided
 Use sprinkler irrigation to keep salt
washed into soil profile

17. Managing Salty Soils
 Saline Seeps
 Changing topography of soil to create a
low point where water (w/ dissolved salts)
can seep out of soil & be collected
 Add plantings to help utilize the water

18. Assignment