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MADE POSSIBLE BY
THE MAIZE TRUST
12
W
E HAVE HAD A LOOK AT SOIL FERTILITY,
MANAGING YOUR CROPS AND CROP ROTA-
TIONS IN A PRODUCTION SYSTEM TO BUILD
HUMUS, THE MAIN PLANT NUTRIENTS HELD
BY THE SAND CLAY AND LOAM COLLOID
AND ENHANCING THE COMPLEX SOIL MICROBES TOGETH-
ER WITH THE APPLICATION OF FERTILISERS IN PREVIOUS
PULA IMVULA
ARTICLES. PLEASE REFER TO THESE TO RE-
FRESH AND IMPROVE YOUR KNOWLEDGE BASE.
An important aspect of growing commercial crops on your soil is to
know and understand what the pH or acidity level of the soils is, in
the various soil types, occurring on your farm by measuring them
when doing soil testing or prior to planning a comprehensive liming
programme. If they are extremely acid or alkaline then the soil can
be ‘corrected’ by applying various compounds including calcitic or
dolomitic lime in a carefully planned short, medium and long-term
application programme to each land in turn.
If your high potential and deepest soils are very acid you might be
missing out on obtaining the highest crop yields in optimum rainfall
years. Adding a ton or more of maize yield per year over many years can
amount to a considerable increase in income and thus economic sustain-
ability in future years. At a value of R2 500 per ton over five years this
would be R12 500.
Delaying the analysis of a potential acidity problem and the imple-
mentation of a properly planned liming programme can be very costly
especially when profitable crop production demands high yields. The
direct costs for maize depending on the yield target or potential of the
soils under consideration can cover a range of R7 000 to R10 000 per
hectare for dryland production. This implies that a yield of 2,8 t/ha to
4 t/ha is required to cover the direct costs per hectare. Any yields
over this will go towards your fixed costs such as bond repayments,
land lease payments, rental, electricity as
defined by your accounting methods and
programmes. It is vital to assess your yield
potential from detailed farm records. Most
farmers over-estimate their actual long-term
yields when doing their gross margin analysis.
UNDERSTANDING PH
pH can be measured in a water medium or in
a chemical buffer medium of water and calci-
um chloride. Be sure to know which one you
are using. The range of pH and ideal plant
growth and pH (CaCl
2
) is shown in
Figure 1
.
Table 1
gives an indication of the potential
yield to an ideal soil pH reading. For example,
if you are planting maize in a land that has a
1
Crop
Soil pH
4,7
5
5,7
6,8
7,5
Relative yield (100 is best and 0 is worst) ratio to ideal
Maize
34
73
83
100
85
Wheat
68
78
89
100
99
Soybeans
65
79
80
100
93
Oats
77
93
99
98
100
Lucerne
2
9
42
100
100
Grasses
31
47
66
100
95
Crop yields relative to pH.
CONSEQUENCES
of not liming your acid soils
Photo: Jenny Mathews
Richard McPherson, Pula Imvula
contributor. Send an email to
richard@agrimetrix.co.za