Geology Reference
In-Depth Information
1.2
1.0
Gm
0.8
Upper limit in theory
Cr
Kk
0.6
Vi
L
b
Ld
0.4
ASIALAND sites
ACIAR sites - sandy soils
other ACIAR sites
Kd
0.2
Km
Cm
0.0
0
3
6
9
12
15
Ratio of the percent of coarse to fine materials
Fig. 11.8
The relationship between the ratio of coarse to fine materials and the average soil erodibility for
ASIALAND and ACIAR sites. The dashed line represents the best fit for the four ASIALAND sites. For the ACIAR
sandy soils, the ratio of percentage of sand (>0.02 mm) to the sum of percentage of silt and clay from mechanical
analysis is used. For all other sites, the ratio of coarse particles (both primary particles and aggregates >0.5 mm) to
fine particles (
0.5 mm) obtained using the wet-sieving technique is used. Other legends are: Ld, Luodian, China;
Kd, Kuala Dal, Malaysia; Cm, Chiang Mai, Thailand; Cr, Chiang Rai, Thailand; Gm, Goomboorian, Australia;
Km, Kemaman, Malaysia; Lb, Los Banos, the Philippines; Vi, VISCA, the Philippines; Kk, Khon Kaen, Thailand.
Reproduced with permission from Yu
et al
. (1999).
≤
dashed line fitted to data from ASIALAND sites
in Fig. 11.8 is given by:
in fine soil fraction could be correlated with
increased soil strength, and/or with decreased
depositability (which increases
c
t
(Equation (11.8) ),
thus decreasing
b
(Equation (11.11) ).
There are a number of implications, if not con-
clusions, from this comparative study of soil
erodibility at ASIALAND and ACIAR sites.
Firstly, variability in the erodibility parameter
is considerable, both site to site and event to
event. Secondly, the soil erodibility parameter
is positively related to wet-sieved particle sizes,
although the nature and reliability of this rela-
tionship are uncertain, and further compilation
of the calculated soil erodibility values is clearly
needed in order to provide greater confidence in
such a predictive relationship. Thirdly, for sandy
soils, the soil erodibility approaches its theoreti-
b
=
0.246
+
0.139
Q
(11.23)
Also included in Fig. 11.8 are the results of data
from the ACIAR experiments presented earlier in
this chapter (see Table 11.3). Whilst the line fit
shown in Fig. 11.8 and Equation (11.23) is to the
ASIALAND data, the main discrepancies of
the data from ACIAR sites from this line are for
the two Philippines sites, which suggest a curvi-
linear relationship. However, as noted earlier, the
frequent cultivation required for manual weed
control may have led to the high erodibility of these
two clay soil sites. The decrease in
b
with increase
