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GRAANGIDS
2017
GRAIN GUIDE
Analysis of samples
Leading laboratories in South Africa are affiliated with AgriLASA (Agri Laboratory Association
of Southern Africa), which handles the quality control for laboratories in South Africa. These
laboratories use analytical methods that have been calibrated for South African conditions. Soil
samples should be sent to such a laboratory. Usually the pH, acid saturation, P, K, Ca, Mg and
Na levels are reported, but sometimes also S, exchangeable Al
3+
, micro elements and other
appropriate values. Analysis laboratories must specify in their report which analytical methods
were used to determine each nutrient element.
It does not really help producers to send samples to foreign laboratories. They use other methods
(extractants) to determine the nutrient status. Their recommendations have also been developed
for their soils and their specific climate, and differ drastically from the locally developed norms.
Processing of data
Raw data is captured in software programmes (GIS = geographical information systems) and
integrated with the global positioning system (GPS) points. Point data is then interpolated to
calculate values for any position in the field between the sampling points and this is then known
as a surface. The accuracy of the interpolated data depends to a great extent on the statistical
models with which the interpolation is done. Service providers should use recognised models.
Report
A report is then compiled, containing at least the maps of the respective analysis parameters.
In addition, prescription maps for correcting deficiencies can be included. Sometimes a written
report is presented in which the analysis parameters are interpreted and discussed, with
recommendations for corrections.
Prescription maps
The final product comprises prescription maps for the differential correction of deficiencies
and imbalances. Strictly speaking, these prescription maps must be compiled by or under the
supervision of a SARNAP-registered soil scientist or agronomist. The prescription maps are then
captured with the software (data chip) of differential equipment in agricultural implements, which
apply the ameliorants as required across the field, as needed per area. It is also possible to
implement prescription maps in agricultural implements without differential equipment. This is
done by loading the prescription map on a mobile GPS and then physically marking the zones
in the field. The spreading can then be done in increments by an ordinary spreader without GPS
equipment. This is not completely differential, but a good second prize.
Soil surveys
Soil surveys involve mapping the distribution of soil types occurring on the farm and using this as
basis for deducing field capacity or potentials. Soil surveys are carried out by SARNAP-registered
soil scientists to adjust crop production practices differentially according to soil types and
derivatives.
BE ON THE LOOKOUT FOR
QUALITY
PRECISION SERVICES
Continued from the back of the Implements tab page
Continued on p. 44