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As always, cost follows quality, but real efficiency and quality needs to be
carefully taken into account when making final calculations.
Quantity
A light textured soil with an effective cation exchange capacity (CEC) of
5 centi-mole charge per kg (milli-equivalents per 100 gram soil) and with
an acid saturation percentage of 20%, will have one milli-equivalent of
acid to neutralise in each 100 g of soil.
In a hectare of light textured soil at a depth of 30 cm deep, there are
4,5 million kg of soil. This means that 45 million milli-equivalents
(milligram) of acid need to be neutralised. This translates to 45 kg of acid
per hectare. As calculated above, 50 g pure calcitic lime is needed to
neutralise one mole or equivalent or gram of acid. So 45 kg of acid will
require 2 250 kg pure calcite to neutralise. A soil with a CEC of 10 and the
same acid saturation, will need double the amount of pure calcite.
If a 100% calcium oxide nano suspension (absolutely pure and reactive)
is used, one will still need 2,25 ton/1,78 (higher efficiency) = 1,26 tons
lime per ha or 1 260 kg/1,3 kg/litre (reported density) = 969 litres per ha.
Even if pure magnesium oxide is used, one would still need 0,9 tons or
692 litres. Usually, the suspension products contain low concentrations
of actual lime and that will elevate the mass requirement dramatically.
A 15% calcium oxide suspension will require 100/15 x 969 litres =
6 460 litres per hectare using the same reported density.
The fact remains, that no matter how pure or reactive (fine) one can get
any natural liming material, one cannot exceed an efficiency of 2,5 times
that of pure calcitic lime. Furthermore, there simply is a huge mass of
pure acid in a hectare of acidic soil and one accordingly needs a pro-rata
high mass of lime material to neutralise it.
Movement of lime
Lime in any form, micro or nano fine, powder or suspension, will only
move in a coarse textured matrix with no reactive sites. Soil is simply
not that. Soil contains reactive clay and minerals that will react with lime
on contact, especially when it is fine and reactive. For that reason, one
needs to be careful of overemphasized claims of mobility of any liming
product in natural soil.
In summary
The ability of a lime material to neutralise acid in the soil, depends on
the efficiency and quality of the material and the quantity applied must
be sufficient to neutralise the actual quantity of acid in the soil. Even
when the best product in terms of neutralisation capacity (efficiency
and quality) is applied in too small a quantity, the result will be totally
insufficient and uneconomical.
The hope is expressed that this article gives some perspective and will
save the producer money and reduce associated risk when making a
choice of liming material and the quantity of application thereof.
Reference
Bornman, J.J., Coetzee, J.E.K. & Van Vuuren, J.A.J. 1988. Inter-laboratory study with regard
to the variability of three aglime analysis methods, including a resin suspension method.
Comm. Soil Plant Anal
. 19 (3) 299 - 310.
