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
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.