Agricultural Lime Association - Mineral Products Association
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  Fertiliser utilisation  

Lime is a fertaliser

The availability of plant nutrients is affected by the pH of soil. The major plant nutrients nitrogen (N), phosphorus (P) and potash (K), as well as calcium and magnesium, show a marked reduction in availability in acid conditions.

The diagram below shows the scale of availability. It illustrates the risk of shortage of iron, manganese and boron in alkaline conditions which, if not monitored, can give rise to specific problems in fruit and some root crops. The most important and significant illustration, however, is the increasing unavailability of the major and most commonly applied plant nutrients, nitrogen, phosphate and potash (N, P, and K) with increasing acidity. Maintaining an adequate balance annually requires constant attention and necessitates regular crop inspection and field-walking practice.

The addition of lime helps to release soil nutrients. Fertilisers and manure cannot be fully effective if the land is short of lime. In addition water that leaches from acid soils may contain undesirable materials which can adversely affect the quality of surface and groundwaters.

Accuracy and good practice in lime application is a vital consideration for ALA members.

Heightened environmental controls and regulations on the disposal of sewage and other industrial wastes to landfill or sea outfalls have led to an annually increasing volume of application to agricultural land. These products can bring beneficial residual fertiliser and organic matter to the soil. However, problems do arise as these wastes also contain a number of metallic and other inorganic Potentially Toxic Elements (PTEs). With repeated applications these contaminants accumulate in the soil and can remain indefinitely, causing restrictions on plant growth, increased uptake of metals by animals and man via the food chain and reductions in soil microbial activity. Heavy metals become more available in acid soils and adverse effects will then increase. When sludge or waste is applied there will be a need to maintain alkaline pH values for an indefinite period thereby inhibiting the release of heavy metals, whilst gaining the manurial values of the material.



The coloured bands show how liming makes essential plant nutrients more available and toxic aluminium less available. A pH of 6.5-7.0 (just on the acid side of neutral) is the best level.

When straw is incorporated there is a need to encourage the activity of aerobic bacteria to accelerate decomposition. Bacteria can only flourish when the lime status is maintained.

With the fixed and other variable costs to add to the cost of fertilisers, to say nothing of rent, and return on capital, it is essential that the correct pH level for the crop to be grown is looked upon as good agricultural practice in the efficient management of any profitable operation.

Regular liming in order to maintain appropriate pH levels also helps in achieving the right balance between profitable farming and environmental protection.

Certainly there are few improvements so easily and cheaply carried out which can have so fundamental an effect on the success or failure of crops and farming.



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