Unit 11: Acidic Soils

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Unit 11 Acidic Soils Salt-Affected Soils

• Chapter 8

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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?

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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

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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

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/Soil_Aluminum_and_test_interpretation.htm
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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

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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

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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

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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

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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)

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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

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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)

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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

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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

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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

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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

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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

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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

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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.

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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

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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

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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

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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)

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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

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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

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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

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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

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Assignment