- Applying lime (calcium carbonate) is the most practical way of reversing soil acidification
- Lime should be considered once the soil pH drops below pHCa 5.0 if sensitive species are to be grown successfully
- Lime is usually applied during summer or autumn because the heavy truck loads require firm ground, although it can be applied at any time of the year
|
- In the Corangamite region, more than half the cropping and dairy land is subjected to regular applications of agricultural lime (Bluett and Ward pers. comms. 2003)
- On broadacre grazing, less than 10% of land has lime applied regularly, because it is generally not cost-effective. As an alternative, land managers may grow more acid-tolerant pasture species
|
Understanding the question
|
| Why is it important to me as a farmer?
|
- The process of soil acidification is a potentially serious land degradation issue
- Without treatment, soil acidification will have a major impact on agricultural productivity and
sustainable farming systems and acidification can also extend into subsoil layers posing
serious problems for plant root development and remedial action
|
- In some regions, there has been a drop of one pH unit over the last 20 to 30 years
- Already, some farming areas have lost the ability to grow preferred agricultural species
such as phalaris and lucerne simply because, without lime, the soil is too acid
|
| How and why acidification occurs
|
- Soil acidity occurs naturally in higher rainfall areas and can vary according to the
landscape geology, clay mineralogy, soil texture and buffering capacity
- Soil acidification is a natural process, accelerated by some agricultural practices (See figure 1)
- When plant material is removed from the paddock, alkalinity is also removed and contributes to increases in soil acidity
- When grain, pasture and animal products are harvested from a paddock, the soil is left more acid. Hay removal is particularly acidifying because large amounts of product are removed
- More significantly, soil acidification is most often a result of nitrate leaching. Nitrogen is
added to the soil in a number of ways:
- nitrogen fixed by legume-based plants
- as nitrogen based fertilisers
- from breakdown of organic matter
- dung and urine
- Acidification occurs in agricultural soils as a result of the:
- removal of plant and animal products
- leaching of excess nitrate
- addition of some nitrogen based fertilisers
- build-up in mostly plant-based organic matter
|
|
| How to recognise acidification in the paddock
|
- The symptoms of soil acidity include:
- Uneven pasture growth
- Poor nodulation of legumes
- Stunted root growth and high incidence of root diseases
- Invasion of acid-tolerant weeds (for example, fog grass, sorrel, geranium)
- Difficulty establishing lucerne, phalaris, and medics
- Formation of organic mats on the ground surface due to reduced biological
activity
|
Figure 2 - Indicator dye and powder can be used to show acidification in soil in the
field (acid soils turn orange/yellow).
- Photo courtesy of Chris Gazey (DAFWA)
|
| Managing the application of lime to reverse soil
acidification
|
1. Undertake Soil Testing
- 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 soils acidity or alkalinity because:
- testing is relatively easy
- field equipment to measure pH is relatively inexpensive
- Field test kits are available that use colour to indicate pH levels. The kits are
inexpensive, easy to use and will test a lot of samples but should not 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. Professional soil
analysis is recommended and sending soil samples to a recognised laboratory ensures
the most accurate results
- Soil testing ensures that excess nitrogen is not being applied through fertilisers; unused
nitrogen may leach and cause soil acidification. Within the region, only about 10% of
landholders regularly conduct soil tests. Therefore nitrogen leaching could be significant,
particularly on sandy soils
|
2. Application of Lime
Introduction
- The only way to reverse soil acidification is to raise the pH through the application of
alkaline minerals such as agricultural lime to the soil. The effectiveness of an application
of lime will depend on the relationship between:
- pH
- soil type - generally, coarse textured soils (eg. sands) need less lime than finer
textured soils. Also, low organic matter soils need less lime than peaty soils
- buffering capacity - the soil�s ability to resist a change in its pH level and is largely
determined by the soil texture
- enterprise
- The primary active component in agricultural lime is calcium carbonate
- Lime raises soil pH making it less acidic
- It increases nutrients availability and stimulates microbial & earthworm activity
- Lime decreases the availability of toxic elements (Al, Mn & Fe)
- It helps stabilise soil structure with the addition of calcium
How and when to apply lime
- Lime can be incorporated into the soil or simply top-dressed and left to leach into the soil with subsequent rainfall
- A lime requirement test will incorporate these affects when used to determine the amount of lime needed to raise soil pH. Other factors needed to determine an appropriate lime rate include target pH of the specific plant, lime quality, application method and economics
- Lime can restore productivity in acid soils and should be considered once the pH drops below pHCa 5.0 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. Conversely, you may not get a response to some nutrients if the soils are too acid. A holistic balanced approached is necessary
- 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
Figure 3 � Critical values for lime application.
- Source: DEPI Victoria
- Most lime is spread by contractors because of the need for specialised equipment due to the nature of the product and the large quantities applied. Lime is usually applied during summer or autumn because the heavy truck loads require firm ground, although it can be applied at any time of the year
- 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 and settle at pHCa 3.8 to 4.2
- 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 1.5 tonnes a hectare on sandy soils is needed to increase pH by one unit
- Lime moves slowly (0.5 to 1 cm per year) through the soil profile via the soil macropore structure. Incorporation into the soil profile, where possible, will assist effective treatment
- In permanent pasture situations, spreading the lime on the surface and allowing it to work its way into the soil is acceptable. Surface application is better than no application
|
- Lime application at sowing:
- Lime is relatively insoluble (does not dissolve easily). Thus, it is slow to react. For
maximum benefit, it should be worked into the soil when resowing a pasture or
sowing a summer fodder crop
- Limes from Southern Victoria are generally �softer� and tend to partially dissolve in water compared with �harder� limes of other regions, such that there is less need to incorporate these with cultivation or have them ground finer
- Lime application as a top dressing:
- Lime can be applied as a topdressing (in other words, spread on uncultivated soil
or existing pasture) if a paddock is to remain in the pasture phase for several
years
- In the past, surface-applied lime was not recommended because earlier research
indicated that 18 to 24 months might be required before a rise in soil pH was
measured. This period of time was often needed to allow movement of the lime
into the soil (0.5 to 1 cm each year) and to allow for the chemical reactions to
occur.
|
- However, much uncertainty still surrounds the likely responses to surface-applied
lime. Without doubt, most pastures on very acidic soils (less than pHCa 4.3)
will respond to surface-applied lime over a period of time. Pastures on soils with
very high levels of aluminium or manganese will also respond
Figure 3 - Soil pH trends throughout the different seasons in soils with and without
lime.. - Source: DEPI Victoria (From Hollier & Hall 1997). [View larger image]
- Lime Benefit Calculator � Soilquality.org.au
- This calculator provides a simple means of determining economic benefits of lime
application. It requires the user to make informed estimates of yield change
across a ten year period
|
Other related questions in the Brown Book
|
|
Brown Book content has been based on published information listed in the Resources and References sections below
|
|
|
- Soil pH - Soil Health Knowledge Bank � Department of Agriculture, Fisheries and
Forestry
- Fertilising Pastures :(Chapter 5)- Greener Pastures for south west Victoria (2006) �
Department of Environment and Primary Industries, Victoria
- Soil Acidity - South West Victoria SoilSmart Series: (Clarkson 2003) � Corangamite
CMA Soil Health Outputs
|
- Clarkson T, Department of Primary Industries on behalf of the Corangamite Catchment
Management Authority (2007). Corangamite Soil Health Strategy 2007. Corangamite
Catchment Management Authority, Colac, Victoria.
- Victorian Department of Primary Industries (2011), Soil Types and Structures Module.
|
- Managing Soil Factors That Can Limit Plant Growth. Section 4.5 - Department of
Primary Industries, Victoria.
- Acid Soils. Victorian Resources Online - Department of Primary Industries, Victoria.
|
|
