Agriculture Reference
In-Depth Information
Penetration resistance (MPa)
1
2
3
4
5
6
7
8
0
Critical penetration
resistance at FC
10
20
Wheel
track
30
40
50
60
Vine
70
row
Figure 7.2
The effect of wheeled traffic on soil
compaction in the inter-row of a sandy
soil (after Myburgh et al. 1998).
80
stantial amount of water at relatively high
m
values. The concept of readily avail-
able water (
RAW
)—water released between
10 kPa and
40 to
60 kPa—
was introduced in section 6.5.1. A
RAW
value
70 mm per m depth is consid-
ered most desirable.
Drainage and Aeration
Good drainage and aeration are usually complementary soil attributes. A soil
should drain rapidly from saturation to field capacity, at which point all the macro-
pores are air-filled. The resultant air-filled porosity or
air capacity
(see box 3.6)
should be at least 10-15% to allow an adequate rate of O
2
and CO
2
diffusion.
7.1.4
Table 7.2
Examples of
PAW
a
in Soils of Different Texture,
Adjusted for the Rooting Depth of Grapevines
Soil Texture
Sandy Loam
Uniform or
Rooting Depth
Over Clay
Gradational Clay
(m)
Loamy Sand
(Duplex Profile)
Loam
1.0
100
150
180
1.5
150
225
270
2.0
200
300
360
3.0
300
450
540
a
Expressed as mm of water in the soil profile
