Agriculture Reference
In-Depth Information
Infiltration Rates
IR
for Soils of Different Texture and Structural Condition
Table 7.1
IR
at Steady State
Typical Texture and
(mm/hr)
Grading of the
IR
Structural Condition
0-10
Very poor
Heavy clay soils with poor structure (often
degraded by cultivation)
Clay soils with moderately good structure
Loam, clay loam soils, some sandy soils, usually
good structure
Loam to sandy soils with very good structure;
clay or clay loam soils of the Krasnozem type
10-20
Poor
20-50
Moderate
50
Good
increases with
BD
. The
BD
of vineyard soils can increase, particularly in the
inter-row areas because of compaction by machinery, such as tractors, spray equip-
ment, and harvesters. Typically, compaction occurs at depths between 20 and 25
cm and is more severe in sandy soils than in clay loams and clays (except when
the clays are sodic; see section 7.2.3). Figure 7.2 shows the marked difference in
soil compaction, measured by penetration resistance, under a wheel track and un-
der a vine row on a sandy soil in a vineyard.
Available Water Capacity
The
available water capacity
(
AWC
) is calculated from the difference between the
soil's water content
7.1.3
at field capacity
FC
and permanent wilting point
PWP
(sec-
tion 6.2.2). The
AWC
, expressed in mm water per m depth, depends primarily
on the soil's texture and structure. However, the
plant available water
(
PAW
) de-
pends on both the
AWC
and on the rooting depth of the plant. A rooting depth
of at least 60 cm is desirable for irrigated vines, and up to 2 m for mature non-
m
.
The relationship between soil strength and soil matric potential
Figure 7.1
3.0
BD = 1.55
BD = 1.85
2.0
BD = 1.25
1.0
-100
-10
0
Soil
Ψ
m
(kPa)