Acid soilaction investment for your soil now for the future

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ACID SOIL ACTION
INVESTMENT

ACID SOIL ACTION

N O W

A N D

FOR

F O R

YOUR

T H E

SOIL

F U T U R E

A practical decision support guide to assess the problem & manage the risk.


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Cover

ACID SOIL ACTION
INVESTMENT
N O W

A N D

FOR

F O R

YOUR

T H E

SOIL

F U T U R E

Contents
About this kit

3

Getting started

5

How to use the kit ............................................................................................................................5
What’s in it for me?............................................................................................................................5
Support material ................................................................................................................................5
Why worry about acid soils?

7

Nature of the problem ......................................................................................................................8
The acid attack ................................................................................................................................10
The cost ..........................................................................................................................................11
Benefits of action ............................................................................................................................13
Understanding acidity

17

What can you do to stop soils becoming more acid? ....................................................................17
What needs to be done? ................................................................................................................17
Soil pH - What does the figure mean? ............................................................................................22
The strategies ..................................................................................................................................23
Interpreting soil pH..........................................................................................................................24
What do I need to do?

29

Acid soil management decision ......................................................................................................29
Action Guide for soil acidity

39

Check the signs................................................................................................................................39

Indicators of Acid Soil......................................................................................................................41
Taking soil samples ..........................................................................................................................44
Measuring soil pH ............................................................................................................................46
Possible causes ................................................................................................................................47
Monitoring checklist ........................................................................................................................48
Field texture ....................................................................................................................................50
How much lime?

53

To maintain production level ..........................................................................................................53
To increase soil pH to grow sensitive plants ..................................................................................53
Lime Guide

63

Which liming material is best? ........................................................................................................63
Types of lime....................................................................................................................................65
Comparing limes..............................................................................................................................67
Managing soil acidity - technical note series

69

Lime suppliers

103

Soil acidity profile maps

109

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Acknowledgments
This publication is intended as a guide for farmers,
advisers and industry field representatives to help
assess acid soil problems and decide on
appropriate management strategies. The kit has
been designed and compiled by Carole Hollier,
Agriculture Victoria, Rutherglen with the assistance
of numerous colleagues in research, extension and
industry. The technical information has been
supplied by many sources and is gratefully
acknowledged. Special thanks to Anna Ridley, Bill
Slattery, Eloise Rich, Agriculture Victoria; Greg
Fenton, NSW Agriculture; Brian Hughes, Primary
Industries, South Australia; Mike Frost, Limestone
Association of Australia; and Trevor Tovey, David
Mitchell Limited.
Special thanks also to the farmers in south-eastern
Australia who provided crucial input in determining
what problems to address and how to present
information – especially the 12 farmer collaborators in
north-eastern Victoria for their valuable contribution.
Suggestions for improving the manual are most
welcome.
The kit has been funded by the Land and Water
Resources Research and Development Corporation,
as part of the National Soil Acidification Program.

© Department of Natural Resources and Environment 1999.
DISCLAIMER
This publication may be of assistance to you but the State
of Victoria and its employees do not guarantee that the
publication is without flaw of any kind or is wholly
appropriate for your particular purposes and therefore
disclaims all liability for any error, loss of other consequence
which may arise from you relying on any information in this
publication.
ISBN 0 7311 4309 4

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This kit is for...
Farmers who:
• are not aware of the impact of soil acidity
• know they have a problem, but are not sure of the implications
• are ready to act, but unsure of what to do
• have made some attempts at soil diagnosis/management, but unsystematically
• are uncomfortable with the technical level of data in available materials
• are uncertain about management options, costs, benefits, time scales
• need clear, practical information
• are ready to act further, but need clear options

and industry/farm advisers who:
• know about acid soils but want to update their skills
• are busy people and want a quick reference guide
• talk to farmers to help solve their problems
• require industry information (lime sources/quality)
• want more detail

It features:
• action-oriented information: what to do next
• clear steps, essential minimum information only
• clear recommendations to assist decision making
• organised around tasks, not topics
• easy to use planning and recording tools
• basic guide to cost-benefits of alternative approaches

Follow the tractors:
Go to page 5 to get started

The kit will be successful if you:
• are convinced to test for soil acidity
• implement monitoring or action strategies in the current year
• seek further support and information
• establish new farm management practices to minimise
soil acidification
• move to a whole farm planning approach
• obtain increases in yield and profitability by
implementing a liming strategy

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Soil acidification - Is your farm at risk?
If acid is attacking your soil and burning a hole in the farm account Acid Soil Action
- a practical decision support system to encourage step-wise adoption of management
options - is for you.
It aims to increase awareness of the impact of soil acidification and knowledge of
management options to reduce soil acidity.

How to use the kit
You can read single sheets or work through the whole package.
A series of colour coded tractors makes your information search and
decision making easier. This “go to” approach is designed to guide

your decision making process. You decide the level of involvement

For example,
Go to page x

and your technical information needs.
The tractor symbols will drive you through the awareness and assessment of soil
acidification into management options to improve farm management decisions.
It provides direction for further information and action.

What’s in it for me?
The material is divided into colour coded sections. The first section introduces acid soils
and describes the nature of the problem. It helps you answer the question; Is acidification
an issue for my farm?
The second part is a step-wise farm management decision support system followed by
a series of technical information updates. For many land managers the information sheets
and work plans will not go into enough depth. They are designed to provide a starting
point to build individual knowledge and improve discussions with your farm adviser.

Support material
This resource kit can be adapted for discussion groups
or group activities (such as Landcare) to update
skill base on recognising acid soil problems
and appropriate farm management options.
Photographs and illustrations help to
reinforce key elements for your

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management decisions. Technical terms are explained on the most relevant
sheet and a glossary of terms is provided.
However, the package is not complete. It is designed as an initial building block to add
specific information and relevant material from other sources for your region and
industry.
Your local Department of Agriculture will be able to supply you with a range of resource
material and can advise on commercial soil testing packages. Research results from local
or regional lime evaluation or acidification studies may also be available.
With the help of this guide, you can make an initial assessment of an acid soil problem
and determine, in consultation with your farm adviser and Australian Fertiliser Services
Association local lime suppliers, management actions to minimise and treat acidification
and boost productivity.

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The process of soil acidification or change in the amount of acid in the soil is a serious
land degradation issue. Without treatment soil acidification will have a major impact on
agricultural productivity and sustainable farming systems.
Ninety million hectares of agricultural land in Australia is acid and at risk of further soil
degradation. Nearly half of this land is already strongly acid (pHCa<4.8) and requires
urgent action for sustainable production.
The area damaged by acidification is increasing and many soils are acidifying with current
agricultural practices. Without treatment, acidification is extending into subsoil layers
posing serious problems for plant root development and remedial action.
For most acid soils, the most practical management option is to add lime to increase
surface soil pH.

Extent of Soil Acidity in Australia

MILLIONS OF HECTARES

35
30
25
20
15
10
5
0
NSW

Vic

WA

Highly Acidic
(pHCa<4.8)

SA

Qld

Tas

Moderate Acidity
(pHCa 4.9 - 5.5)

For more information:
Go to map section on page 109

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Nature of the problem
Soil acidification is a natural process, accelerated by some agricultural practices.
In some regions, there has been a drop of one pH unit over the last 20-30 years.
Already, some farming areas have lost the ability to grow preferred agricultural species

such as phalaris and canola simply because, without lime, the soil is too acid.
Many clover-based annual pastures
are becoming progressively more
acid over time. In cropping areas,
where subterranean clover pastures
are an important part of cereal
growing, soil pH decline trends are
emerging.
If soils are allowed to become
extremely acid there is a risk of
irreversible soil texture change.
If subsoils are allowed to acidify, treatment is extremely difficult and costly.
Acid soil problems can cause poor establishment, growth and persistence of pastures and
crops. These soils are characterised by plant nutrient imbalances, toxicities and
deficiencies that reduce plant growth.
Aluminium toxicity is the major problem associated with acid soils. As soil becomes more
acid, aluminium becomes more available to the plant and stunts root growth.
Acidification has been described as a ‘sleeping giant’. Unlike dryland salinity, it is insidious
with few visual symptoms.
Symptoms of reduced growth in acid soils are often subtle and can be explained
away by other factors, such as poor season or inadequate fertiliser. It is only over a
period of time (usually decades) that major problems become apparent.
Problems are likely to develop if you farm:
• in high rainfall areas (greater than 500mm/rainfall) with dry summers
• annual pasture systems
• lightly textured soil
• with legume rotations
• and have a history of nitrogenous fertiliser use
• with high product removal, particularly lucerne.

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In most grazing systems acidification processes work unnoticed - until pasture production
declines. The rate of acidification in pastures depends on the species grown. In cropping
systems, lack of plant vigour in sensitive species and reduced yields are more obvious.

Soil acidification is linked to other degradation issues. The water using capacity of
agricultural systems is reduced as soils become more acid. Valuable perennial species such
as lucerne and phalaris, recommended to reduce recharge and the impact of salinisation,
are sensitive to aluminium toxicity and will not establish and grow.
Other economically important species, such as canola, barley and most varieties of wheat
are also sensitive to acidity.
Accelerated acidification occurs in
agricultural soils as a result of:
• removal of plant and animal products
• leaching of excess nitrate
• addition of some nitrogen based
fertilisers
• build up in organic matter, largely of
plant origin.
The more acid the soil, the fewer the
choices of crops and pastures that will
grow productively. Even acid tolerant

Some acid soils support productive systems but
acidification processes can be masked.

plants show a reduction in growth.

Soil alkalinity removed by some farm products (kilograms)
Product

Yield

Lime equivalent
per year (kilograms)

Lucerne hay

3-7 tonnes per hectare

360 to 840

Clover/grass hay

3-7 tonnes per hectare

270 to 630

Lupins

0.6 to 1.3 tonnes per hectare

12 to 26

Wheat

1.2 to 2.1 tonnes per hectare

11 to 19

10 lambs

per hectare

6

6kg of wool

per sheep

0.8

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The causes of soil acidity

Source: NSW Agriculture Agfact 19 Soil acidity and liming

The acid attack
Acidity itself is not responsible for restricting plant growth. The associated chemical
changes in the soil can restrict the availability of essential plant nutrients
(for example, phosphorus, molybdenum) and increase the availability of toxic
elements (for example, aluminium, manganese). Essential plant nutrients can also be
leached below the rooting zone. Biological processes favourable to plant growth may
be affected adversely by acidity.
Acid soils have a major effect on plant productivity once the soil pHCa falls below 5.
pHCa 6.5

Optimum for most plant growth. Neutral soil. Trace elements may become
unavailable.

pHCa 5.5

Balance of major nutrients and trace elements available.

pHCa 5

Below pH5 aluminium may become soluble in the soil depending on soil type.
Phosphorus combines with aluminium and may be less available to plants.

pHCa 4.5

Manganese becomes soluble and toxic to plants in some soils.
Molybdenum is less available. Soil bacterial activity slows down.

Aluminium becomes soluble in toxic quantities.

pHCa 4

1 0

Soil structural damage.

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The effects of soil pH on aluminium.
4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

Aluminium Toxicity
Increasing

calcium

aluminium
phosphates
iron

Insoluble complexes of aluminium, iron and phosphorus are found in this pH range.

The Cost
Acidification is costing the national agricultural economy around $300 million each year.
Beyond farm-gate impacts triple this cost to the community.
The impacts of soil acidification are potentially enormous and include:
• increasing dryland salinity
• increasing nitrate pollution of groundwater and reduced water quality
• reduced plant yields, farm income and domestic/export earnings
• reduced options for agriculture
• reduced vegetative cover and accelerated water runoff and erosion
• irreversible degradation of the clay content of soil, hence reduced fertility
• declining pH of waterways and aquatic environment
• increased infrastructure cost
• decreased land values.

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Off Site Impact

Acidification

Water table rise

Increased nitrate
leaching

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Salinity

Increased
erosion

Sediment on roads
and drains

Reduced nitrate
uptake

Phosphorus in streams

Reduced water
uptake

Turbidity in streams

Sediment in streams
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Increased runoff

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Nitrate pollution of ground
water

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Reduced plant
growth

Infrastructure damage

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Increased flooding

Reduced biodiversity and
reduced choice of species

Death of acid
sensitive species

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Benefits of action
If preventative or remedial strategies are put in place, acidification can be slowed down or
soil pH (the measure of acidity) adjusted so that a wide range of plant species can be
successfully grown.
Lime application will increase soil
pH and:
• improve temperate legume
nodulation
• reduce available aluminium and

manganese
• increase molybdenum (Mo),
calcium (Ca) and phosphorus (P)
availability
• provide a more favourable
environment for soil microbes
• improve nutrient cycling by earthworms and soil bacteria
• help reduce other forms of land degradation (for example salinity, erosion)
• increase cropping/pasture options so more sensitive or valuable species can be grown.
Plants respond to lime in different ways. Altering soil pH affects the availability of
nutrients and also influences soil microbial activity. Some crop and pasture species are
more tolerant or sensitive to acidity than others. Plant production responses also vary
depending upon soil type and environmental factors.
There is more dry matter production where lime responses are seen. Because soil growing
long term perennial pastures are higher in organic matter than cropping soils, they often
require larger amounts of lime to obtain a similar response.
Responses to lime have been inconsistent on some acid soils. Subject to soil pH
and plant species, visual responses are sometimes seen in autumn/winter but
more commonly in spring. Dry matter responses to lime with pastures based
on tolerant species have been generally small and inconsistent.

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Yield increase
Research has shown that applying lime to an acid soil can make the difference as to
whether barley will or will not grow and will significantly increase yields of canola, wheat
and triticale. Benefits have also been seen with faba beans, chick peas and the more tolerant
pasture species such as clovers and cocksfoot. Sensitive species such as phalaris and lucerne
respond dramatically to lime application on acid soils. Trials have shown subterranean
clover production responses ranging from 10 to 50% on acid soils in cropping areas.

Research at Agriculture Victoria – Rutherglen has shown improved canola (right)
and wheat (left) yields with 2.5 t/ha lime application to raise soil pH.

Research data has shown that responses to lime can be profitable where soil pH is
strongly acid. Most economic advantage is achieved by liming highly productive
perennial pastures or sensitive crops and pastures such as canola and lucerne.

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Understanding soil pH
Soil pH is one of the most routinely measured soil parameters. It is used as a benchmark to
interpret soil chemical processes and governs the availability of many essential or toxic
elements for plant growth.

Soil pH is a common measure of the soil’s acidity or alkalinity because:
• testing is relatively easy
• laboratory and field equipment to measure pH is not expensive.
Sending soil samples to a laboratory is recommended to ensure the most accurate results.
Test kits are available that use colour to indicate pH levels. The kits are cheap (around
$20), easy to use and will test a lot of samples but cannot be relied on for decisions such as
rates of lime application. Test kits will only tell you whether your soil is acid or alkaline.
A number of compact testing meters that can be used out in the paddock are available, most
of which are capable of giving accurate results if used correctly. They range from $130 to $500.
Topsoil and subsoil pH testing is recommended. When interpreting plant responses based
on soil pH, the surface (A horizon) and sub-surface (B horizon) need to be considered.
There are two common measurements of soil acidity or alkalinity - pH as measured in water
(pHw) and pH as measured in 0.01M CaCl2 (pHCa), both at a soil to solution ratio of 1:5.
Soil test reports usually provide soil pH results measured in both calcium chloride and water.
The soil pH as measured in water is considered to be closer to the pH that the plant roots
are exposed to in the soil. But it is subject to large variation within the paddock because of
seasonal changes in soil moisture and the ionic concentration of the soil solution which is
related to the amount of total salts in the soil. Research has shown that seasonal variation
of pH measured in water can vary up to 0.6 of a pH unit in any one year.
In comparison, the measurements of soil pHCa is less affected by seasons. Farmers can take soil
samples at different times during the year without affecting the final diagnosis or interpretation.
Soil pHCa measurements in Australia vary from pH 3.6 to pH 8 for a range of
different soil textures (sandy loams to heavy clays). Soil pHw values lie
between 4 and 9.
Higher pHw values to around 10 may be associated with alkali mineral
soils containing sodium carbonates and bicarbonates. Soil pHw
less than 4 may arise from oxidation of sulfides in acid
sulphate soil (confined to North Coast NSW and
sub-coastal mangrove soils) or from highly
organic peat conditions.

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Some tips...
• Soil testing will tell you the current acidity status of your paddock. If your soil
pH measured in calcium chloride (pHCa) is above 5.5 then there is little immediate
risk of acidity.
• Lime can restore productivity in acid soils and should be considered once the pH drops
below pHCa5 if sensitive species are to be grown successfully.

• You are unlikely to get responses to lime if other nutrients are lacking. This should show
up in a soil test or plant tissue analysis and should be corrected.
• Lime responses are generally seen in the first and second year for cropping systems, but
can take up to five years depending on soil type, rainfall and lime quality for permanent
pasture systems.
• It is necessary to re-lime your paddock (about every 10 years), depending on the rate of
re-acidification.
• If paddocks with an acidity problem are not limed, the soil pH will continue to fall.
• The amount of lime you need to apply varies according to soil type - field experiments
have shown that up to 5 tonnes a hectare on clay loams and down to 1.5 tonnes a
hectare on sandy soils is needed to increase pH by one unit.
• Lime moves slowly (0.5 to 1cm yr) down the soil profile, so incorporation is
recommended where possible.
• In grazing situations, spreading the lime on the surface and allowing it to work its way
into the soil is recommended. Surface application is better than no application.
• Soil pH is measured in either water or in calcium chloride. When measured in calcium
chloride, the result is lower than pH measured in water.
• The pH using the water method may be higher by 0.6 to 1.2 in low salinity soils and
higher by 0.1 to 0.5 in high salinity soils. Research has shown a difference of 0.8 for a
large range of soils.

pH measured in calcium chloride
4

5

6

7

extremely
acid

neutral

4

5

6

7

pH measured in water

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What can you do to stop soils becoming more acid?
• Recognise soil acidity
• Monitor soil pH
• Know crop and pasture requirements
• Keep accurate records for each paddock
The aim of monitoring soil acidity (knowing your current soil pH status) is to identify
problems at an early stage and not at the crisis management stage when production loss is
severe and remedial treatment expensive.
Do not assume that every paddock has the same soil pH or acidification rate across
your farm.

Your management options:
• Use acid tolerant plant species. (Remember this is only a short-term strategy as the soil
will continue to acidify over time.)
• Apply lime at a rate based on soil pH, soil type, rainfall and land use.
• Reduce the rate of acidification
- sow perennial pasture to reduce nitrate leaching
- match fertilisers to plant requirements, monitor plant and soil nutrient levels,

use least acidifying nitrogen fertilisers
- recycle nutrients and alkalinity by feeding hay back onto paddocks

What needs to be done?
• Soil test
• When should lime
be applied?

Go to page 39
Action Guide for Soil Acidity

Lime neutralises surface soil acidity
and helps prevent future subsoil acidity.
If your soil pHCa is below 4.5 you will
need to apply lime as soon as possible
to regain productive yields. On less acid
soils (pHCa 4.5 to 5) liming within the
next few years will help prevent future
acidification.

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for more details

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If you intend to grow sensitive species an urgent lime requirement
may be needed. Soil pH needs to be kept above pHCa5.5.
Lime requirement will depend on:
• current soil pH (topsoil and subsoil)
• target pH
• type of crop or pasture
• soil texture
• lime quality.

The target pHCa for most acid soils is 5.5.
Target soil pH
Land use

pH (CaCl2)

pHw

Extensive grazing

5.2

6.0

Intensive grazing

5.5

6.3

5.5 to 6.5

6.0 to 7.0

Subsoil acidity
Sensitive species
Horticulture (most crops)

Application rates vary according to
your soil type. Heavier textured soils
require more lime to raise the soil
pH. Most acid soils need at least 1.5
to 2.5t/ha to raise pH in the top
10cm by half a unit. Use 1.5t/ha
for sandy soil; 2t/ha for a clay
loam; and 2.5t/ha for a clay
soil. Lime works best when it is
finely ground and incorporated
into the soil.

Subsoil acidity:

• Target pH after liming needs to be pHCa
greater than 5.5 for lime to effect the subsoil.
• When surface pHCa falls below 5 acidity starts to move into
the subsoil

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How much lime?

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• Select the right nitrogen fertiliser

Choose nitrogen fertiliser carefully and aim to use the least
acidifying fertilisers. The most acidifying nitrogen fertilisers
are ammonium sulphate and mono-ammonium phosphate
(MAP) and the least acidifying nitrogen fertiliser is potassium
nitrate.

Effects of different fertilisers on soil acidity
Highly acidifying

Nitrogen fertilisers
• Mono-ammonium phosphate (MAP)
• Sulphate of ammonia
• Di-ammonium phosphate (DAP)
• Ammonium nitrate
• Anhydrous Ammonia
• Urea

Slightly-acidifying

For more detail:
Go to page 93
Acidifying fertilisers

• Replace nutrients
Soils become more acid when crop and pasture products leave the farm gate and lime
equivalents and soil nutrients are not replaced; for example lucerne hay removal is
very acidifying to the soil. Soil test or plant tissue analysis will tell you what
nutrients your soil needs - see your local agronomist or farm adviser to help
interpret your test results and nutrients requirements.

Go to page 56
Amount of lime needed to neutralise
acidification caused by product removal

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• Monitor and keep records
Implement a regular soil testing program. Remember you may not see an immediate
response to any farm practice you introduce to reduce acidity. Keeping good records
helps you track your progress and compare performance.
Soil testing is the first step to identify an acid soil problem and decide on future
management actions.
Soil testing is the only way to determine the
severity of acidity as decline in production
associated with acidification is a gradual and

often subtle process.
Your soil test report alone may be insufficient
because factors related to soil acidity may not
be the major limitation to production. Seek a
specialist with local knowledge to help interpret your

Go to page 22
Soil pH - What does the
figure mean?

soil test results.

Your decision to manage acid soils should be viewed as a:
•

Preventative strategy

- to ensure continuous, profitable farming

•

Remedial strategy

- to fix it now
If your soil pHCa is above 5.5
Your only decision is to MONITOR
acidity with regular soil testing
Target pHCa 5.5

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pH of common substances
pH (water) values

pH of common substances
14
Caustic soda

13

Ammonia

12
Milk of magnesia

11

Increasingly
Alkaline

Soap solution

10

Sea water
9
8
Blood

7
Normal soil
pH range

Pure Water

Fresh milk
6

Optimum growth range

5

Increasingly
Acidic

4
3

Sour milk
Wine
Vinegar

2

Lemon juice

1

Battery acid
Sulphuric acid

0

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Soil pH - What does the figure mean?
Topsoil (0-10cm)
pHCa less than 4

pHCa 4 to 4.5

pHCa 4.5 to 5

pHCa 5 to 6.5

pHCa 6.5 to 7.5

weathered low
fertility soils

natural or induced
process

critical level with
optimum growth
of acid tolerant
plants providing

adequate fertiliser
supplied

optimal growth
of most plants

neutral
no soil acidity
affect on
production

natural or
induced by very
acidifying
agricultural
practices where
buffering
capacity reduced

acidification
associated with
nitrate leaching from
improved pasture,
fertiliser effects,
removal of alkali in
produce

effects of toxicities
of exchangeable
manganese (Mn)

in some soils may
still limit
production of
sensitive plants

no soil acidity affect
on production other
than possibly
manganese below
pHCa 5.8

acid sulphate
soils confined to
coastal and sub
coastal low lying
areas

process of mineral
weathering
dominant

below pHCa 4.8
aluminium (Al)
toxicity will begin
to limit production

soils likely to be
productive
providing no
nutrient deficiencies

or degradation
effects (eg. salinity)

exchangeable
cations such as
aluminium (Al) and
manganese (Mn)
exhibit toxicity to
plant roots

Amelioration
economically
viable

toxicity increasing in
concentrations with
decreasing soil pH

Liming strategy
needs to be
determined
according to
acidification rate
of farming system.

deficiencies of
nutrients such as
molybdenum (Mo)
can occur
populations and

activity of some
microorganisms
affected

DECISION:
• Change the soil pH to grow acid-sensitive
crop or pasture or,

• Maintain current pH and level of production

soil type and organic
matter controlling
soil buffering
capacity (ability to
resist pH change)
determines the rate
a soil is likely to
decrease in pH

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How much lime?

•

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The strategies
Topsoil (0-10cm)
pHCa less than 4

pHCa 4 to 4.5
Increase in
available aluminium

pHCa 4.5 to 5

pHCa 5 to 6.5

Acid soil problem severe
Urgent action required to
continue agricultural
practice. Implement
remedial strategy or

risk irreversible soil
structure damage
severe nutrient toxicities
and deficiencies

Acid soil problems likely
Beginning of soil texture
breakdown.
Acid soil infertility
Nutrient toxicities and
deficiency likely
Check aluminium levels
in topsoil and if greater
than 5 mg kg -1 LIME
Values for exchangeable
Al generally greater than
70 mg kg -1 in this soil
range
Soils characterised by
low CEC levels (less than
5 milli equivalents/100g)
are likely to develop acid
problems.

Acid soil problems
likely

Values for
exchangeable Al
generally less

than
5 mg kg -1
Can grow all
species
providing
nutrient
requirements are
met.

Lime it or lose it for
future agriculture.

Values for
exchangeable
Al generally
vary from 5 to
70 mg kg -1
Go to page 79 for more information
on aluminium interpretation
or revisit page 18

Lime strategy

What species do you
grow?
Remedial action depends If ACID TOLERANT
you don’t need to
on:
lime but monitor so
Clay content (texture)

that soil pH doesn’t
Organic carbon (greater
fall below pHCa 4.5.
than 2%)
If your species
Cation Exchange
selection is moderate
Capacity (CEC). If less
or sensitive to acid
than 5 me % can only be soils you will need to
increased by organic
LIME TO ABOVE
carbon. CEC 5 to 8 me % pHCa5. At pHCa4.8
or higher and Ca + Mg% and above Al toxicity
CEC high, further acidifi- is unlikely. Only
cation unlikely or process toxicities of Mn, if
very slow.
present will affect
plant yield.

pH<4
Careful planning
required before
doing anything

Check subsoil pH

MONITOR to
maintain pHCa
above 5. Regular

soil testing (at
least every five
years).

Check subsoil pH
Which management
strategy?

How much lime?
To get to productive
stage, minimum 3t/ha high
grade lime to increase soil
to above pHCa 4.5
sow only acid tolerant
species
economics of liming may
be prohibitive
rethink land value and use

If acid need lime sooner
than later because lime
moves slowly (0.5 to 1cm
yr) down the soil profile.
Minimum 2 to 3.5 t/ha
high grade lime to
increase topsoil pH 0.5
to 1 unit.
ONLY option acid tolerant
species plus lime.

Remedial strategy to
increase soil pH and
the choice of species
you can grow
Preventative strategy
to maintain current
production level and
prevent gradual pH
decline.

What type of lime?
Application
• Incorporation: If practical, fastest result.
• Surface application: Prior sowing,
autumn break
• Timing: Ideally season before sowing
sensitive species or prior sowing. Lime
can be applied any time of the year.

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Which liming material
is best

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How much lime?

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Interpreting soil pH
Soil pH governs the availability of many elements that are
essential for, or toxic to plant growth. It is the measure of
the hydrogen activity in solution indicating the intensity of

Go to page 15
Understanding soil pH

acidity or alkalinity.

1000

Relative ion concentration

With each unit drop in
soil pH the number of
hydrogen ions multiplies

by 10. At pH 7 the
hydrogen and hydroxyl
ions are in balance. At
pH 6 there are 10 times
more hydrogen ions; at
pH 5 there are 100 times
more hydrogen ions, and
at pH 4 there are 1000
times more hydrogen
ions. As this graph
shows, the concentration
of hydrogen ions
increases dramatically
below pH 5. Above pH 9
the concentration of
hydroxyl ions increases
rapidly.

500

1.0

500

1000
10

9

8

7

6

5

4

It is the imbalance of the nutrients and other chemicals, caused by the acidity, that
affects plant growth. Interpretation of soil pH is greatly improved knowing other
soil measurements such as electrical conductivity, effective cation exchange
capacity and the concentration of each exchangeable cation.
Knowing your soil pH and estimating your target soil pH to grow sensitive species is
essential in determining lime requirement. However, interpretation of pH for plant
production relies on the ability to match the results with studies that have
determined responses for the same soil type and climatic conditions. If there were
no other limiting factors, optimum soil pH for a plant species would be the same for
all soil types. This is rarely the case because in strongly acidic soils other limitations as
well as low pH are usually present.

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Aluminium
Soil clay minerals contain aluminium but it has no impact on plant productivity unless the
soil pHCa falls below 4.8 (pHw less than 5.5). Below pH 4.8Ca aluminium (Al) becomes toxic
and root growth is severely reduced in sensitive and moderately sensitive plant species.
A damaged root system reduces the plant’s ability to obtain nutrients and water from the
soil. As a result there is a significant decrease in plant yield.
Plants vary in their tolerance to Al. Tolerant species, for example
lupins, some wheat cultivars, triticale and cocksfoot may achieve
maximum yield potential without significant effects on plant
growth due to Al toxicity.
Growing tolerant species needs to be considered as a short-term
option to manage acid soils. Soils will continue to acidify over time.

For more information:
Go to page 78
Measuring aluminium

Soil pHCa below 4.3

Soil pHCa 4.3 to 4.8

Soil pHCa above 4.8

Al concentrations increase
to levels that affect even the
most tolerant plants

Al concentrations increase
to levels that will affect the
most sensitive species

Al concentration extremely
low and not likely to be
toxic to plant growth.

Significant decrease in
plant yield
Exchangeable Al greater
than 70 mg kg -1

Significant decrease in
plant yield
Exchangeable Al varies
from 5 to 70 mg kg -1

Values for exchangeable
Al generally less than
5 mg kg -1

(0.78 cmol (+) kg -1)

(0.06 to 0.78 cmol (+) kg-1)

(less than 0.06 cmol (+) kg -1)

Manganese (Mn)
At low pH and in high concentrations, manganese can
become toxic to plant growth but not in all soil types.
Some soils do not contain high levels of Mn even at low
pH. Aluminium has a dominant effect at low pH.
Seasonal fluctuations in Mn may vary in wet or dry soil.

Revisit page 30 for interpreting
aluminium level from a soil test.
What do I need to do?

Concentrations increase in waterlogged soils or poorly drained soils in
spring, when warm and wet conditions coincide. Elevated Mn
concentrations may also occur in hot, dry summer but the
likely period of toxicity in species other than lucerne
is in autumn after the first rains. Above soil pHCa
5.5 Mn is not toxic to plant growth.

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