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Unit 11: Acidic Soils & Salt-Affected Soils

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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

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