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MADE POSSIBLE BY
THE MAIZE TRUST
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pH of 4,7 compared to a pH of 6,8 you might
only realise 34% of the possible maximum
yield for that soil. In the deep but extremely
acid soils in KwaZulu-Natal yields have been
increased from 2,5 t/ha to over 8 t/ha by
correcting the soil pH through a long-term
liming programme. This might take several
applications amounting to between five and
seven tons of the recommendation of calcitic or dolomitic lime. Dolo-
mitic lime containing magnesium is recommended when the calcium
to magnesium ratio in your soils needs correcting as well.
These are general observations that indicate trends. Each farm-
er would get a feel for what are the ideal applications and results
of lime applications on his own soils over many years. The general
rule of thumb is that a particular application of lime reacts in the soil
colloidal complex over about three seasons to affect the planned
for change in pH desired. Seasonal tests in your lands will show the
progress being made towards an ideal pH of 6,8. Increasing crop
yields realised will also indicate the effectiveness of the current lim-
ing programme.
In considering total cation exchange capacity (CEC) your test
might come back showing an acid saturation of 30% to 40% which
is a very acid soil. In simple terms this means that 30% to 40% of
the spaces, in the soil colloidal medium, to hold the major nutrients
such as potassium, sulphur, and calcium are taken up by hydrogen
ions. The soil is thus not able to hold or keep the nutrients required
to enable the crops grown to achieve maximum yields. Liming will
improve the ability of the soil to retain nutrients that the plants can
access over the vegetative and seed forming stages.
SOIL CORRECTION PLAN OR STRATEGY
A total soil correction strategy might involve the application of calcitic or
dolomitic lime to improve pH, gypsum to balance sulphur, MAP to improve
phosphate status and KCL to correct the potassium status. If applied by a
contractor this recipe might cost between R1 850 and R2 500 per hectare.
This might be a bridge to far for some farmers and the ideal soil will rather
be created over several years.
Considering only liming, the costs depending on the farm’s distance
from the lime source could range for delivered product from R600 to
R700 per ton with and an application cost of R200/ha for farmers using
contractors. KwaZulu-Natal farmers in the main apply the lime with
their own equipment.
Work out your costs of a liming programme, together with an
agronomist you are comfortable with, and weigh up this cost against
the estimated financial gains from the increased yields over several
seasons. Start with your highest potential soils and plan to correct
each land on the farm in turn over several years to spread the financial
cost and risk to you farming business.
CONCLUSION
Experienced farmers, agronomists, fertiliser agents, consultants, and
other experts in the field are of the opinion that ‘liming works’. But con-
sider the financial implications and risk before launching into a full liming
programme. Do it systematically for every high potential land on your
farm. Those farmers that have access to grant funds should use any op-
portunity offered, as soon as practically possible, to apply lime as a start
to creating an ideal soil that will ensure higher yields into the future.
1
A soil pH of 5,2 to 8,0 provides optimum conditions for most commercial agricultural crops.
Lime spreading.
Photo: Jenny Mathews
Making a plan – applying lime with a fertiliser spreader.
Photo: Jenny Mathews