unit 11: acidic soils & salt- affected soils chapter 8
TRANSCRIPT
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