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

Application methods for lime Reclaiming & managing salt-affected

soils

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

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

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

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

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

Composition of Lime

Lime standard treatment for acidic soilsLiming 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

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

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%

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?

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

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

http://www.spectrumanalytic.com/support/library/ff/Soil_Aluminum_and_test_interpretation.htm

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

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

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

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

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)

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

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)

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

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

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

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

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

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

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.

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

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

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

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)

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

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

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

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

Assignment