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Unit 11: Acidic Soils

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Unit 11: Acidic Soils & Salt-Affected Soils Chapter 8 Objectives Impacts/Causes/Effects of soil acidity & salinity Action of lime in the soil & products available ... – PowerPoint PPT presentation

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Title: Unit 11: Acidic Soils


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 lt 4.7 Al toxic to most plants
  • Areas receiving gt30 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 pHs 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
  • Dont 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.com/support/library/ff
/Soil_Aluminum_and_test_interpretation.htm
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 lt10 organic matter our
    target pH should be 6.5
  • Soil nutrients more/less available at varying pHs

17
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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
  • 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 330-500/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 (gt3-4 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/ plants 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 lt5 exchangeable Na
    for some fruits, other woody ornamentals lt.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 gt8.5
  • 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 lt8.5
  • Attempts to improve condition by leaching results
    in sodic soil

29
Salt Balance
  • 23 of worlds 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 cant 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
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