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46

GRAANGIDS

2017

GRAIN GUIDE

Tillage of soils in South Africa summarised

The wide variety of soil types found in the crop

areas of South Africa makes it difficult to provide

standard prescriptions for tillage. This wide variety

is attributed particularly to the great variation in

soil properties, climate and the accompanying

production potential.

However, if the soils are

grouped according to the specific climate

zone and texture classes, a few general tillage

guidelines can be provided.

Summer rainfall of between 400 mm and

550 mm per year

Red and yellow sandy soils with less than

6% clay in the topsoil

This group is found mainly in the central

production areas (Western Free State, North

West and Northern Cape) and comprise wind-

deposited soils with less than 6% clay in the

topsoil, less than 8% clay in the subsoil and an

apedal (single-grained) structure. Hutton and

Clovelly soils are the main soil types in this

class. These soils are extremely vulnerable to

wind erosion and subsoil compaction, fertility

is low, as is the water retention capacity in

the absence of a barrier layer. However, soil

types that lack a barrier layer, like the Avalon,

Kimberley and Molopo soils, have a higher

water retention capacity within the root zone.

In order to combat wind erosion and soil-

borne plant diseases and to ensure good root

development, mulch tillage combined with a

deep ripper action, controlled track traffic and

a good crop rotation system are recommended

as the most sustainable system in these soils.

The depth of the water table can be managed

with the aid of a fallow system to the extent that

it is kept about 1 200 mm from the soil surface.

In seasons with excessively high rainfall the

plant establishment can be increased, and a

catch crop can even be used to lower the levels.

Red and yellow sandy soils with 6% to

18% clay in the topsoil

These soils mostly have a poorly developed

structure in the topsoil and consequently have

strong crust-forming properties that lead

to poor aeration and infiltration. The most

common soils in this group are the Clovelly,

Hutton, Bainsvlei, Bloemdal, Avalon, Pinedene

and Kimberley soils. These soils are also subject

to compaction, and if the clay content of the

topsoil is less than 10%, there is also a risk of

wind erosion.

The recommended practices in these soils are

conventional clean tillage, combined with a

ripper action of approximately 350 mm deep

where soil compaction is a problem. As crust

formation is the single biggest problem in

these soils, regular shallow tillage after rain is

required to ensure good infiltration. However,

tillage practices like mulch tillage can be

applied to this soil, provided primary tining to

a depth of 300 mm forms part of the system.

In the shallow, stony soils of the winter rainfall

areas (Western and Southern Cape) tining at

a depth of 150 mm before or during planting

should be adequate.

Soils with between 18% and 25% clay in

the topsoil

Because of the higher clay content of these

soils the structural grade is usually moderate or

stronger. This group contains a large variety of

soils like the Valsrivier, Sepane, Oakleaf

Hutton and Clovelly

Bainsvlei and Bloemdal

Continued on p. 49

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