There are three important aspects for fruit growers to consider when purchasing lime for their orchards. These are fineness of lime, neutralising value (NV) and source of lime material, advises Lismore District Horticulturist, Ross Loebel.
Liming materials are now covered under the Fertilizers Act 1985. Lime must have a minimum of 30% calcium, a neutralising value of at least 70%, and 80% of it must be finer than 0.7 mm. Particles larger than about 0.7 mm are not effective in reducing acidity of soil. Finer particle size will react quicker with the soil.
The capacity of a liming material to neutralize the soil acidity is expressed as its neutralising value(NV). The higher the NV, the greater the ability of the product to raise soil pH. Calcium and magnesium carbonate are the effective components of limestone.
Small amounts of magnesium are often desirable where magnesium levels are low, especially in some parts of the Lismore district. Too much magnesium may cause nutrient imbalances in some soils.
Growers should check the NV of lime before buying to ensure value for money. The following table illustrates the NV of different pure forms of liming materials.
|Source||% Neutralising Value|
|Calcium carbonate (lime)||100|
|Magnesium carbonate (magnesite)||119|
|Calcium Hydroxide (slaked lime)||135|
|Calcium oxide (quick lime)||178|
|Source: Liming materials that contain more than 8% magnesium and more than 16% calcium are called dolomite.|
Where appreciable amounts of magnesium carbonate are present, the NV of the liming material can be greater than 100%.
DATE: September 1986
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