Environmental Engineering Reference
In-Depth Information
sodium adsorption ratio (SAR), percent sodium (%Na), and residual sodium
carbonate(RSC)(Raju
2007
; Raju et al.
2009
).Stuyfzand(
1989
) classified water
intosevendivisionsonthebasisoftheCl
−
concentration: 22 %, 11 %, 45 %, 11 %
and 11 % in pre-monsoon and 11 %, 33 %, 34 %, 11 % and 11 % in post-monsoon
season samples are extremely fresh, very fresh, fresh, fresh brackish and brackish-
brackish category of waters, respectively (Table
2
).ECisameasureofthedegreein
which water conducts electricity. Salty water conducts electricity more readily than
purewater,henceisroutinelyusedtomeasuresalinity.TheUSSalinityLaboratory
(Richards
1954
)classiiedgroundwateronthebasisoftheEC:33%and56%in
pre-monsoon and 22 % and 78 % in post-monsoon are good and fair category
waters, respectively (Table
2
).
Sodium concentration is important in classifying irrigation water because sodium
reacts with soil to reduce its permeability. Excess sodium in water produces unde-
sirable effects of changing soil properties and reducing soil permeability (Kelley
1951
). In all natural waters percent of sodium content is important parameter to
evaluate its suitability for agricultural purposes (Wilcox
1955
). The calculated val-
ues of percent sodium range from 36.86 to 73.98 with an average of 51.58 in pre-
monsoon and 27.2 to 65.96 with an average of 44.18 in post-monsoon seasons. A
maximum of 60 % sodium in groundwater is allowed for agricultural purposes
(Ramakrishna
1998
). The chemical quality of groundwater samples was studied
from plots of percentage of sodium and electrical conductivity on the Wilcox dia-
gram (Fig.
7
). Wilcox diagram revealed that, out of nine groundwater samples in the
study area, 34 % and 22 % samples belong to excellent to good category, 22 % and
56 % belong to good to permissible category, 33 % and 11 % belong to permissible
to doubtful category, followed by 11 % and 11 % belonging to doubtful to unsuit-
able category in pre- and post-monsoon seasons, respectively (Fig.
7
).
The agricultural crop yields are generally low in lands irrigated with waters
belonging to doubtful to unsuitable category. This is probably due to the presence of
excess sodium salts in groundwater, which causes osmotic effects on soil-plant sys-
tem. When the concentration of sodium is high in irrigation water, sodium ions tend
tobeadsorbedbyclayparticles,displacingMgandCaions.Thisexchangeprocess
of Na
+
inwaterforCa
2+
and Mg
2+
in soil reduces the permeability and eventually
results in soil with poor internal drainage (Raju
2007
). Hence, air and water circula-
tion is restricted during wet conditions and such soils are usually hard when dry
(CollinsandJenkins
1996
; Saleh et al.
1999
).
Sodium adsorption ratio (SAR) is used to determine the relative concentrations
of sodium, calcium and magnesium in irrigation water and to serve as an indicator
of the potential damaging effects of these ions on soil structure and permeability
(Raju et al.
2011
). Typically, a SAR value below 3.0 is considered very safe for turf
grasses.Overtime,waterwithaSARof9.0orabovecancausesigniicantstructural
damage to clay soils. Sandy soils are not susceptible to structural and permeability
problems and can tolerate higher SAR values (~10) in most cases. The SAR value
is most likely to be affected by irrigation water. The SAR values range from 1.45 to
8.28 with an average of 3.49 in pre-monsoon and 1.12 to 6.43 with an average of 2.82 in
Search WWH ::
Custom Search