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

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Presentation on theme: "Unit 11: Acidic Soils & Salt- Affected Soils Chapter 8."— Presentation transcript:

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 CaCO 3 available  Lime purities can be expressed w/ a CaCO 3 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 t/library/ff/Soil_Aluminum_and_test_inter pretation.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 <10% organic matter – our target pH should be ~6.5  Soil nutrients more/less available at varying pH’s

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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 ~ #/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: 1. Establish internal drainage If not already adequate May require tile installation, ditching Can be impractical/costly 2. Replace excess exchangeable Na  Necessary for sodic & saline-sodic soils  Extent varies w/ soil texture, clay, quality of available water extent of damage 3. 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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