4.3 USSL diagramTo determine the su

4.3 USSL diagram
To determine the suitability of water to irrigation, two important parameters, namely, salinity
hazard and sodium hazard are highly required. In the USSL diagram these two parameters
are used to clearly indicate whether the water under study is suitable for irrigation or not. The
total concentrations of soluble salts in irrigation water can be classified into low (C1),
medium (C2), high (C3) and very high (C4) salinity zones. These zones (C1 to C4) have the
value of EC less than 250 μS/cm, 250 to 750 μS/cm, 750 to 2,250 μS/cm and more than
2,250 μS/cm, respectively. Higher EC in water creates a saline soil. If water used for
irrigation is high in Na+ and low in Ca 2+ , the ionexchange
complex may become saturated
with Na + , which destroys soil structure, because of dispersion of clay particlesUS Salinity Laboratory’s diagram (US Salinity Laboratory Staff, 1954) is used widely for
rating the irrigation waters. Plot of geochemical data of groundwater samples of the study
area in the USSL diagram is illustrated in Figure.3. During both the monsoon seasons, wells
belonging to the 1 st layer fall in the C4S2 and C4S3 region. C4S2 and C4S3 are not good for
irrigation and since all the wells of 1 st layer falls in this region, water in this region is
unsuitable for irrigation. 2 nd layer of well samples falls in the C3S2 and C3S1. This rating
indicates high salinity and lowmedium
sodium hazards and the wells falling in this region
are also not suitable for irrigation. Third layer also follows the same pattern as that of 2 nd
layer. 4 th and 5 th layer of wells falls in the C3S1 and C2S1 and the water from these wells can
be used for irrigation as these contain low sodium content.