Research Article
Characterization of Tubewell Water in Tehsils of District Gujrat
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S. S. H. Kazmi
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K. H. Gill
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M. Mukhtar
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In arid and semiarid region where rains are erratic and scarce, one has to rely upon irrigation through canals and tube wells. Forced by the canal water shortage and increasing cropping intensity to feed the ever-growing population, farmers have been tapping ground water resource on a very large scale (Kijne and Velde, 1990; Javaid et al., 1998). On the other hand, it is reported that about 70 percent tubewell discharge is used in agriculture sector (Anonymous, 1995) and about 75 percent of discharge of existing wells is saltish (Malik et al., 1984b). The use of groundwater of marginal and poor quality without proper mixing may degrade soils, especially at tail end of the system (Mohtadullah, 1997). This practice may also give rise to some apparent and hidden soil problems, directly or indirectly associated with the tubewell irrigations (Javaid et al., 1997).
The canal water supplies are being supplemented with ground water. Out of 16.49 million hectares (m ha) canal commanded area (CCA), 10.07 m ha contain useable and 6.42 m ha saline groundwater. The Punjab gross area in CCA is 10.86 m ha of which 9.19 m ha contain useable and 1.67 m ha contain saline groundwater (Ahmed and Chaudhry, 1968).
Quality of water is of immense importance because poor quality of both surface and groundwater is not only a limiting factor in crop production but also its constant and indiscriminate use cause secondary salinization. The extent and nature of salt accumulation and the degree of soil alkalinity depends on the quality of irrigation water. To avoid indiscriminate use of ground water, proper management practices are deemed necessary, keeping in view the crops to be grown and the soil to be used. The water quality research is also needed to develop management practices.
In Gujrat district underground water is being used for irrigation regularly alone or along with canal water. Thus it is very important to ascertain the quality of underground water used for irrigation. Voluminous work has been done for Punjab but very little information is available at district and tehsil level. In this study an attempt has been made to determine the ground water quality characteristics and relationship for two tehsils of Gujrat district.
The study area was two tehsils (Gujrat and Kharian) of district Gujrat during the years July 1986 to June 1999. Groundwater samples from running tubewells were collected from 160 locations in tehsil Gujrat and 135 locations in tehsils Kharian. These water samples were collected/received in polythene bottles after ½ hour of tubewell operations. The water samples were analyzed within three days for EC, CO3-2, HCO3¯, Cl¯, SO4-2, Na+ and Ca+++Mg++ and then the sodium adsorption ratio (SAR) and residual sodium carbonate (RSC) were calculated (Anonymous, 1954). Based on the values of EC, SAR and RSC, the water samples were categorized using the standards as described by the Soil Fertility Organization (Malik et al., 1984a), which are as under:
The data were grouped for relative frequency distribution. Simple statistical analysis was done and correlations between different water quality parameters were worked out (Steel and Torrie, 1980).
Data (Table 1) indicates that electrical conductivity (EC) ranged from 0.40 to 9.05 dS m-1 for tehsil Gujrat and from 0.54 to 6.44 dS m-1 for tehsil Kharian, with an average value of 1.34 and 1.83 dS m-1 respectively. The coefficient of variation was higher in tehsil Gujrat (88 %) than tehsil Kharian (84 %). It was further observed (Table 2) that 53 percent water of tehsil Gujrat and only 32 percent of tehsil Kharian fall with in safe limits i.e. EC up to 1 dS m-1 which is below the limits described for marginally (1.1 to 1.25) or unfit water (>1.25). These water could be used with out any salinity hazardous. Only 16 and 15 percent water of tehsil Gujrat and Kharian respectively fall under marginally fit category and could be considered manageable while the rest of 31 and 53 percent are unfit water of tehsil Gujrat and Kharian respectively which will cause salinization (Table 2).
The sodium adsorption ratio (SAR) ranged from 0.1 to 21.13 in tehsil Gujrat and 0.1 to 31.52 in tehsil Kharian with an average value of 3.58 and 4.50 respectively (Table 1). The coefficient of variation was higher in tehsil Kharian (102 %) than tehsil Gujrat (93 %). As regard their distribution (Table 2) 83 percent water of tehsil Gujrat and 75 percent of tehsil Kharian fall with in safe limits i.e. SAR < 6 which is below the limits described for marginally (6 10) or unfit water (>10). These waters could be used safely. Only 12 percent of tehsil Gujrat and 18 percent water of tehsil Kharian fall in the range of marginally fit which could be managed without any serious loss to farm production. The rest only few water will promote sodication and could not be used for good crop production.
The residual sodium carbonate (RSC) of tubewell waters ranged from 0 to 11.65 with an average of 2.83 me L-1 in tehsil Gujrat and 0 to 20.50 with an average of 3.17 me L-1 in tehsil Kharian.
Table 1: | Water quality characteristics of tubewells in tehsils of district Gujrat |
Table 2: | Relative frequency distribution (%) of tubewell waters for different quality characteristics in tehsils of district Gujrat |
Table 3: | Regression equations for water quality characteristics of tubewell waters in tehsils of district Gujrat |
**:P<0.01 |
The coefficient of variation was higher in tehsil Kharian (112 %) than tehsil Gujrat (83 %). Considering the relative distribution (Table 2), it was observed that 46% water samples of tehsil Gujrat and 56 percent of tehsil Kharian fall with in safe limits which is far below the limits described for unfit water (>2.5). The uses of these waters will not create any problem. Only 19 percent water samples of each tehsil are in the range of marginally fit and require some special management practices like use of gypsum and flushing with good quality of water (Idris and Shafiq, 1999). The rest of 35 percent of tehsil Gujrat and 25 percent of tehsil Kharian were unfit and could not be used for crop production.
It was observed that correlation among EC, SAR and RSC, SAR is highly significant for both the tehsils (Table 3). In all the parameters marginally fit waters could be manageable with some special management practices, like use of gypsum, flushing with good quality of water, alternate supply of canal water etc. However, unfit waters due to high electrical conductivity will cause salinization (Ghafoor et al., 1990, 1993). To avoid salinization, it was proposed to increase/decrease the depth of bore or change the place of bore to find good quality of water due to variation in water status at different depth (Ahmed and Chaudhry, 1968 and Youns, 1977). The sodium adsorption ratio (SAR) indicates the relative proportion of sodium to calcium+magnesium whereas residual sodium carbonate is an index, which indicates the sodium hazards (sodication of soil). The unfit water samples (containing excess of carbonate and bicarbonate) for irrigation will precipitate soil solution calcium and increase solution sodium, resulting in soil dispersion (Emerson and Bakker, 1973) as well as impaired nutrient uptake by plants (Kanwar and Chaudhry, 1968.).
It is therefore, recommended that unfit water samples may need special management practices if to be used for irrigation but preferably should be avoided because all these factors will combine to lower down the farm production. However, the extent of deteriorating effect of these factors will vary with soil type and management practices.