SOIL PREPARATION

Soil Strength (kPa)

0

500 1000 1500 2000 2500 3000

0

-10

-20

-30

-40

-50

Soil Depth (cm)

-60

-70

04/12/80 11/12/80 18/12/80

-80

FIGURE 3.2: Increase in soil strength with drying of a Hutton soil at Robertson (redrawn after Van Huyssteen, 1983).

Bulk density is the conventional indicator of soil compaction. It indicates what the mass of soil is in a specific volume (including the pore volume) of soil, meaning that the lower the bulk density, the less compact (more porous) the soil is and vice versa. Soil texture also plays a role, and consequently the bulk densities of soils are normally as follows:

clayey soils 1 200 – 1 400 kg/m 3 loamy soils 1 300 – 1 500 kg/m 3 sandy soils 1 400 – 1 600 kg/m 3

In a pot experiment with Chenin blanc/99R, the effects of soil compaction were tested in five soils (Van Huyssteen, 1988). The lower half of 85 dm 3 containers

36 | DETECTION OF ROOT IMPEDIMENTS