About Ag-lime


CHARACTERISTICS OF AG-LIME

Ag-Limes differ in each of the following characteristics. To compare limes, each of these characteristics must be taken into account

ANALYSIS
The analysis of limestone may be quoted in 3 different ways:

  • As a % of Calcium Carbonate
  • As a % of Calcium Oxide
  • As a % of Calcium

The chemical composition of pure limestone rock is 4100% Calcium carbonate (which is the same as 55% Calcium Oxide or 40% Calcium) and 100 Neutralising value. But most Ag-limes are not pure and will therefore have different analysis.

NEUTRALISING VALUE
Neutralising value (NV) is a measure of the ability of a liming material to neutralise acidity compared with pure calcium carbonate. Pure Limestone has a NV of 100. Some materials can have neutralising values greater than 100 (e.g. Quicklime, hydrated lime, magnesium). Most Ag-limes have less than 100NV

IMPURITIES
Most Ag-limes will have impurities and therefore contain less than 40% calcium carbonate and have neutralising values less than 100. Some of these impurities can be beneficial.

FINE & COARSE MATERIAL
To be registered as an Ag-lime, the material must be able to pass through a certain size sieve. Standard Ag-limes typically contain 60% fine material and 40% coarse. While super fine limes contain greater than 95% fine material. The fineness of the material dictates how quickly it can be absorbed. However there is generally a trade off in price as it takes more to crush super fine lime. Also there may be a need to have a larger percentage of coarse material due to the type of crop and the desired frequency of application.

THE COLOUR OF AG-LIME

The type of impurities in the limestone will dictate the colour of the ag-lime. Aag-limes are typically either tan or grey in colour. The colour does not mean that the lime is more or less effective.

WHY APPLY AG-LIME?

"Three changes are constantly taking place in the soil:

      First, acidity is tending to develop.

      Second, humus – the soils content of decomposed organic matter is being used up.

      Third, certain elements essential to plant and animal growth such as calcium are being removed by the harvest of crops       or removed in other ways"
Dr Hopkins (Rothamstead)


INFLUENCE OF pH ON NUTRIENT AVAILABILITY

ENLARGE

Limestone, as a soil conditioner, can help rectify these changes. Lime can be used to neutralise the acidity, it encourages humus to be replenished and it is a good source of calcium. Liming acid soils lowers the toxic levels of aluminium and manganese and increases symbiotic nitrogen fixation in legumes.

Even if all essential elements are present in the soil as a result of fertilizing, it cannot be assumed that they are necessarily available to plants. Availability of minerals to the plant depends on the pH of the soil.

There is considered to be an optimum pH when the most essential elements are available to the soil. That pH is between 6.0 and 7.0 as evidenced in the chart below.

The recommended optimum pH for Sugar Cane, Soybeans and Peanuts Is 6.5

ADVANTAGES FROM LIMING ACID SOILS:

• Lowers toxic levels of aluminium and manganese.

• Increases some microbial activity - decomposition.

• Overcomes the potential for calcium or magnesium deficiencies.

• Increases symbiotic nitrogen fixation in legumes.

• Increases availability of phosphorus and molybdenum.



Difference between Ag-Lime, Burnt Lime and Hydrated Lime

Difference between Ag-Lime, Burnt Lime and Hydrated Lime


Ag-Lime - pulverized limestone rock.
Burnt Lime = Quick Lime - obtained by burning limestone
Used in cement and as a steriliser in times of disease and to hide the smell of disintegrating bodies. While it can be used to improve soil acidity it has an adverse effect on organisms in the soil.

Hydrated Lime = Slaked Lime - produced by adding water to quick lime. Used in the separation of sugar from sugar cane .

Lime Cycle = The unique ability of products derived from limestone to return to their original chemical form. The cycle begins with the pulverizing of the limestone rock, then the burning to form quick lime. Adding water to form hydrated lime is the next step. Carbon dioxide in the atmosphere or from industrial combustion processes react with hydrated lime to convert it back to limestone.

Because of the lime cycle, burnt lime and hydrated lime are always reverting back to their original form. To do this , they use carbon and oxygen from the soil, thereby depleting the soils reserves. Burnt lime and hydrated lime should not be used on soil, even though they may contain high levels of calcium.



THE THREE SOIL CONDITIONERS


Ag/LIME - is high in calcium and has a neutralising value i.e. It reduces acidity / raises the pH level

DOLOMITE - contains both calcium and magnesium and has a neutralising value.

GYPSUM - contains calcium and sulphur but has no neutralising value.




FREQUENCY OF LIMING DEPENDS ON:


• Soil texture.
• Nitrogen fertilization rates.
• Calcium and magnesium crop removal.
• Amount of lime applied.
• Soil pH range desired



THE DO'S AND DON'TS OF APPLY LIME


• Do Order Early – Time between order and supply increases at the height of the spreading season and can be affected by weather conditions.

• Do Apply Early – Lime takes time to work. Consider applying to the last ratoon before planting a break crop.

• Don't apply one week before planting and expect instant results.



REGISTRATION OF AG-LIME
Limes are required to be registered under the Agricultural Standards Act before sale in Queensland. These acts impose requirements on producers with respect to the registration and sale of lime and dolomite as well as fertilisers. In Queensland a product cannot be registered for sale as a lime if the neutralising value is less than 67. To be registered as a dolomite or dolomitic limestone, the product must have a minimum of 8% magnesium in the form of magnesium carbonate. The regulations also require that all of the material should pass through a 3.35 mm sieve.