Water Quality Criteria For Irrigation Biology Essay
Water quality for Irrigation refers to its suitability for agricultural use. The concentration and
composition of dissolved constituents in water can be determined to know its quality for
irrigation use. Quality of water is an important consideration in any appraisal of salinity or
alkalinity conditions in an irrigated area. Good quality of water (good soil and water
management practices) can promote maximum crop yield. The most important chemical and
physical characteristics of water (groundwater & surface water) for irrigation purpose are as
Classification of salinity (EC) in groundwater
EC is an assessment of all soluble salts in samples. The most influential water quality guideline
on crop productivity is the water salinity hazard and is a measure of electrical conductivity (EC).
The higher the EC, the lesser suitable water is available to plants, because plants can only
transpire "pure" water, useable plant water in the soil solution decreases dramatically as EC increases. The amount of water transpired through a crop is directly related to yield; therefore
irrigation water with high EC reduces yield potential.
The Electrical conductivity (EC) of the groundwater in study area varies from 204-1946
/cm and 548 - 2472 µs
/cm in pre-and post-monsoons respectively (Table 5a). Based on the
EC the groundwater of Chinnaeru river basin has been classified into 4 classes after Handa, 1969
(Table 3a). Majority of groundwater samples from both pre- and post- monsoon periods have
medium to high salinity and hence the groundwater is not good for irrigation.
The surface water of the Chinnaeru river basin is comparatively lower EC (Table 5b) than
that of groundwater (Table 5a). Many surface water samples both from pre- to post- monsoons
have low to medium salinity and they are good for irrigation.
The hydrochemical evolution of groundwater can be understood by the plotting the major
cations and anions in piper trilinear diagram (piper, 1944). This diagram reveals similarities and
dissimilarities among groundwater samples because those with similar qualities will tend to plot
together as groups (Todd, 2001). This diagram is very useful in bringing out chemical
relationships among groundwater in more definite terms (Walton, 1970). The geochemical
evolution can be understood from the piper plot, which has been divided into six sub categories
The total concentration of soluble salts in irrigation water can be expressed as low (EC =<250 µS
), medium (250-750 µS cm-1
), high (750-2250 µS cm-1
) and very high (>2250 µS cm-1
classified as C-1, C-2, C-3 and C-4 salinity zones respectively (Richards, 1954, Abhay Kumar
Singh et al.,2011). While a high salt concentration (high EC) in water leads to formation of
saline soil and a high sodium concentration leads to development of an alkaline soil. Salinization
is one of the most prolific adverse environmental impacts associated with irrigation. Saline
condition severely limits the choice of crop, adversely affect crop germination and yields and can
make soils difficult to work. Excessive solutes in irrigation water are a common problem in
semiarid areas where water loss through evaporation is maximum. Salinity problem encountered
in irrigated agriculture are most likely to arise where drainage is poor. This allows the water
table to rise close to the root zone of plants, causing the accumulation of sodium salts in the soil
solution through capillary rise following surface evaporation of water.
The sodium or alkali hazard in the use of water for irrigation is determined by the
absolute and relative concentration of cations and is expressed in terms of sodium adsorption
ratio (SAR). Irrigation water is classified into four categories on the basis of sodium adsorption
ratio (SAR) as: S-1(<10), S-2(10-18), S-3(18-26) and S-4 (>26). There is a significant
relationship between SAR values of irrigation water and the extent to which sodium is adsorbed
by the soil. High sodium and low calcium in water rises the cation-exchange between water and
soil and is responsible for saturated sodium in an irrigated area. This can destroy the soil
structure due to dispersion of Na+ in the clay particles.
The calculated values of SAR for groundwater range from 1.32 to 9.70 in pre-monsoon
and from 1.02–12.10 in post-monsoon periods. The EC ranges for groundwater from 204 to 1946
in pre-monsoon and from 548 to 2472 in post-monsoon periods.
In Wilcox diagram (Fig.11a), The EC is taken as salinity hazard and SAR as alkalinity
hazard, shows low alkalinity hazard (S1) and high salinity hazard (C3) for majority of
groundwater samples from both seasons. However, one sample CR-43 fall in S1-C1 class in pre
monsoon, while few samples from post-monsoon represent medium to high alkalinity hazard (S2-S3) and high to very high salinity (C3-C4). It seems that there is a gradual increase in both
alkalinity and salinity characters from the groundwater samples during pre-to post-monsoon
periods due to long term precipitation and water–rock interaction in space and time.
The calculated values of SAR for surface water range from 1.12 to 8.00 in pre-monsoon
and from 0.72 to 8.40 in post-monsoon. The EC ranges from 190 to 1709 in pre-monsoon and
from 330-2460 in post-monsoon peroids. The surface water samples show a range from S1-S2
alkalinity hazard and C1-C3 range of salinity hazard in pre-monsoon periods, whereas in post
monsoon, the surface water samples show similar alkalinity hazard (S1-S2) but different salinity
hazard (C2-C4) when compared to pre-monsoon period