1. Unit 11: Acidic Soils & Salt-Affected Soils
Chapter 8

2. Objectives Impacts/Causes/Effects of soil acidity & salinity
Action of lime in the soil & products available
Application methods for lime
Reclaiming & managing salt-affected soils

3. Introduction Many adverse affects from acidic & saline soils
Some research says ¾ of humid-region soils need lime
~ 2.5 b ac affected by saline conditions
Salinity can occur from various reasons, various regions
Salinity much harder to manage than acidity

4. Why Some Soils Are Acidic
Most soils become acidic due to leaching
Soil cations leached through soil profile
Favorable soil cations replaced by Al on CEC sites when pH < 4.7 – Al toxic to most plants
Areas receiving >30” rain/yr high risk for acidity, if not managed

5. Why Some Soils Are Acidic
Must have centuries of leaching of cations to acidify naturally
Most acidic soils in the U.S. found:
East of Mississippi River
Pacific coastal soils
Mountain areas
Avg 35” rain/yr – soil pH’s 5-6

6. Ecological Relation of Soil Acidity
Acidic soils usually leached
Strongly acidic soils have:
Few basic cations (Ca, K, Mg, etc.) available for absorption
High amounts of Al, Mn, etc.
Low contents of micros
Toxic levels of Al, Mn
Severely slowed microbial process & N fixation

7. Ecological Relation of Soil Acidity
Acid-tolerant plants have adapted to these conditions well
Don’t require high levels of nutrients
Able to lock up Al

8. Composition of Lime Lime standard treatment for acidic soils
Liming materials:
Calcic Limestone (Ag Lime) – fine ground
Dolomitic Limestone – lime w/ Mg
Quicklime – burned limestone
Hydrated Lime – reaction w/ water to hydroxide form
Marl – lime from bottom of freshwater ponds

9. Composition of Lime Chalk – soft limestone from ocean deposits
Blast surface slag – byproduct of iron industry – has higher P content
Ground oystershell, wood ash – from paper mill, sugar beet plants, fly ash, etc.
Fluid lime – suspension containing any form of usable lime
Gypsum – not lime, but does supply Ca, can help alleviate Al toxicity

10. Composition of Lime Chemical Guarantees of Lime
Limestone seldom pure calcium carbonate
More impurities, lower level of true CaCO3 available
Lime purities can be expressed w/ a CaCO3 equivalent – ex. 85%

11. Composition of Lime Reactivity of Lime
Neutralizing power of lime determined by rate of solubility of the material used
Different forms more/less soluble
Fineness of grind also has great affect
Why?

12. Reactions of Lime Added to Acidic Soils
Addition of lime to an acidic soil eliminates two major (among others) problems
Excess soluble Al (toxic levels)
Slow microbial action
Other benefits to liming
Raised pH reduces excess soluble Mn, & Fe

13. Reactions of Lime Added to Acidic Soils
Ca & Mg (deficient in many acid soils) can be added in one operation w/ Dolomitic lime
Increases availability of P
Makes K usage more efficient
Increases N availability by promoting microbe growth, decomposition of organic matter
Increases plant-available Mo
Keeping pH above 6.5 reduces solubility of heavy (toxic) metals

14. http://www. spectrumanalytic

15. Crops, Lime, & Soil How Much Lime to Apply?
Soluble & exchangeable acidity need to be neutralized to change pH
Especially exchangeable
Acid tolerance
Least: alfalfa, sweet clover
Low: corn, wheat
Moderate: oats, strawberries
High: blueberry, Lespedeza

16. Crops, Lime, & Soil
Increased levels of clay/organic matter, increase amount of lime needed to change pH
Our soils typically <10% organic matter – our target pH should be ~6.5
Soil nutrients more/less available at varying pH’s

18. Crops, Lime, & Soil Methods of Applying Lime
Most effective – apply lime each year
How many do?
More common – add lime when needed in large enough amounts to justify cost
Definitely should apply 4-12 mos before a legume seeding, or few mos before high value crop planting

19. Crops, Lime, & Soil Liming No-till Fields Surface applied
Most effective if incorporated
Liming No-till Fields
No-till fields:
Microbial action is much shallower
Acid layer at/near surface
Typical build-up of fertilizers near surface (top 1-2”)
Liming raises that shallow soil pH, increases effectiveness of fertilizers & chemicals

20. Crops, Lime, & Soil Lime Balance Sheet
Ammonium fertilizers may neutralize 100# of lime/yr
N fertilization most common reason for soil acidification in cropping soils
Can have ~ #/ac lost lime each year
Calls for 1 t/ac addition of lime every 5 yrs (in addition to lime needed to neutralize N fertilization)

21. Acidifying Soils If growing crops preferring acid soils
Use fertilizers w/:
S, Fe, Al compounds, sulfuric acid
Seldom attempted to acidify a soil, unless for specific production purpose

22. 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)

23. 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

24. 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

25. 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

26. 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

27. 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

28. 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

29. 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.

30. 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

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

32. 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

33. 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)

34. 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

35. 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

36. 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

37. 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

38. Assignment