Agriculture Reference
In-Depth Information
Applying the reduction factor to the optimal CWR, the lesser suitable is the soil the
higher is the CWR value. At the end of this evaluation procedure, both the nominal crop
water requirements (N CWR) and the real crop water requirements (R CWR) has been
Rcwr
established. The Irrigation economical and technical Efficiency Index -
Ieff =
-
Ncwr
is the ratio between this two values The range may be variable from 1, that is the optimal
situation, to 2.5, for the not suitable soils.
Table 6. Matching table for irrigation Soil Suitability Classes (from USBR, mod. ISSDS)
2. Moderately
suit
a
ble
3. Marginally
suita
ble
4. Not
suit
able
1. Suitable
Soil
Parameters
ISSDS
classes
ISSDS
cLASSES
ISSDS
classes
ISSDS
classes
Values
Values
Values
Values
TOPSOIL
TEXTURE
USDA
FA or FLA or FL or
FSA
AL or F or FSV or L or A
or AS or FS
SF
S
Subsoil Texture
USDA
FA or FLA or FL or
FSA
AL or F or FSV or L or A
or AS o
r FS
SF
S
Radical Depth (cm)
>=100
5 or 4
<100 ->=50
3
-
-
<50
1 or 2
Stoniness (%)
<=0,1
0 or 1
>0,1 - <=3
2
>3% - <=15
3
>15
4 or 5
Rockness (%)
0
0
-
-
>0 and <=2
1
>2
2-5
Quasi-
excessive
or
low
Excessive,
low or
blocked
1 or 6
or 7
Internal Drainage
good
3
moderate
4
2 or 5
Topsoil Reaction pH
<=9
<9
-
-
>9
9
Subsoil Reaction pH
<=9
<9
-
-
>9
9
Topsoil Carbonates
%
3 or 4 or
5
1-20
<1 or 20-40
1 or 2 or 6
>40
7
-
Subsoil Carbonates
%
3 or 4 or
5
1-20
<1 or 20-40
1 or 2 or 6
>40
7
-
Topsoil salinity
mmhos
<2
0 or 1
-
-
2-4
2
>4
>2
Subsoil salinity
mmhos
<2
0 or 1
-
-
2-4
2
>4
>2
Strong
sheet
and/or
gully
Surface Water
Erosion
Moderate
sheet
Moderate
gully
3 or
>=5
absent
0
1
2 or 4
Slope for drop
irrigation (%)
0-13
1-2
13-21
3
21-35
4
>35
5-6
Slope for sprinkler
irrigation (%)
<=5
5-13
-
-
-
>13
Slope for flowing/
submersion (%)
1
3
-
-
-
>3
Table 7. Reduction factors for calculating the real needs in the soil/land use/irrigation technique map unit
Soil suitability
class
S2. Moderately
suitable
S3. Marginally
suitable
N. Not
suitable
S1. Suitable
Reduction factor
1.0
0.8
0.6
0.4
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