- Some varieties of Groundnuts have some tolerance of acidic soils.
** Lima Beans tolerate acid soils better than most other beans and peas.
*** Refer to paragraph 5 of “Signs of Soil Acidity” on the previous page.
The list above offers only a broad guide, and there are often wide differences between
varieties. For example, some varieties of sorghum are more tolerant of acid soils than
some varieties of rice.
Lime
Agricultural liming material is defined as a material containing Calcium and Magnesium
compounds that is capable of neutralising soil acidity.
Lime is in many ways the key element in the soil. Lime not only makes acid soils
more alkaline, it also makes clay soils easier to cultivate, it reduces the loss of nitrogen
from the soil, it releases phosphorus and potassium which become “locked up” in acid
soils, and it renders harmless some trace elements such as manganese which may be
present in the soil in excessive amounts.
Another attribute of lime, which may become increasingly relevant, is that it
reduces the amount of Strontium-90 that is taken up by the soil.
Application of Lime
It is often a good idea to apply lime to acid soils, especially in humid and high rainfall
regions where large amounts of calcium are leached from the soil.
Even in normal conditions of arable cropping, or grazing by animals, the equivalent
of about 120–500 kg/ha of lime is lost every year, from leaching and by being taken up
by plants and animals.
In these situations many soils, especially sandy ones, slowly become more acidic
unless lime is added to the soil. However if too much lime is applied, this can cause
deficiencies in some other soil elements such as Copper.
Lime should not be applied together with manure, nor before Irish potatoes are
grown.
Different Forms of Lime
Calcium carbonate (CaCO 3 ) in the form of ground limestone (dolomitic limestone is
best), ground chalk, lump chalk, waste (factory) lime, slaked and hydrated lime (calcium
hydroxide), quicklime (calcium oxide), marl, shells and by-products such as slag. Each
of these sources has a different neutralising value. The lime is scattered onto the soil and
then worked into the upper soil layers.
Below are some examples of the amount of lime (CaO, in MT/ha) needed to increase
arable soil pH to about 6.5 (figures in brackets are for applications on to grassland)—
more lime.
22 TONY WINCH
based on soil depths of 200 mm (arable) and 150 mm (grassland); deeper soils require
Further details about lime are available online at: http://minerals.usgs.gov/minerals
and http://www.aglime.org.uk