Study location The study location was Ashuganj-Polashagro-irrigation Quasem, 2011 and World Bank, 2011 . Barkat et al., 2007 Moses et al., 2016 Priya and Pragya 2014 Islam et al., 2013 BADC, 2013), project, Brahmanbaria under administrative control of Bangladesh Agriculture Development Corporation (BADC). It is situated at 24.02ºN to 90.00º E with 10 m altitude above mean sea level. Disposal water of Ashuganj power plant is used for irrigation in the project over eleven thousand hectares of land. This study was conducted during December 2013 to May 2014 at the project areas. Boro is the major irrigated crop of the project areas and power plant disposal water is the main source of irrigation. Supplemental irrigation is also applied using this water in other Robi crops likes wheat, tomato, mustard, broadcast Aman etc. During the study period irrigation was applied to Boro rice.
Collection and analysis of samples Initial soil samples were collected before irrigated the field on 31 December, 2013 from six different plots randomly of the study area at 15 cm depth. During irrigation to rice field with disposed water, six water samples from the same field and four samples from irrigation canals were collected for analysis. After harvesting of the crop eight soil samples were collected again. All soil samples were analyzed in Bangladesh Agricultural University Humboldt soil testing laboratory and water samples in bio-chemistry laboratory of Bangladesh Agricultural University. Soil samples were analyzed for pH, EC, Na, K, Ca, S, P, total N (%) and OC (%) to determine their quality. The disposal water samples were analyzed for pH, EC, Na, K, Ca, Fe, Mg, Zn, Cu, and bi-carbonate to determine its quality.
Suitability of irrigation water The suitability of water for irrigation was classified based on the following parameters and grading: pH: The acidity or basicity of irrigation water is expressed as pH (< 7.0 acidic; > 7.0 basic). The normal pH range for irrigation water is from 6.5 to 8.4 (Ayars and Wescot, 1985). Water is classified as acidic (<5.5), slightly acidic (5.6-6.4), practically neutral (6.5-7.5), slightly alkaline (7.6-8.0), alkaline based (>8.1) on pH values.
Electrical Conductivity: The most influential water quality guideline on crop productivity is the water salinity hazard as measured by electrical conductivity (EC). The primary effect of high EC water on crop productivity is the inability of the plant to compete with ions in the soil solution for water (physiological drought). Based on EC, the water was classified for suitability of irrigation following ( ) and is -1 -1 classified as excellent (<250 µS cm ), good (250-750 µS cm ), -1 -1 permissible (750-2000 µS cm ), doubtful (2000-3000 µS cm ) -1 and unsuitable (>3000 µS cm).
Sodium Adsorption Ratio: The sodium absorption ratio gives a clear idea about the adsorption of sodium by soil. It is the proportion of sodium to calcium and magnesium, which affect the availability of the water to the crop. Based on values of sodium adsorption ratio, the water was classified as normal (<10), low sodic hazard (10-20), medium sodic hazard (20-30), high sodic hazard (30-40), very high sodic hazard (>50) for suitability for irrigation following.
Soluble Sodium Percentage: SSP is important factor to study sodium hazard and used to adjudging the quality of water for agriculture purpose. High percentage of soluble sodium for irrigation may stunt the plant and reduces soil permeability. classified suitability of irrigation water based on SSP values following excellent (<20), good (20-40), permissible (40-60), doubtful (60-80) and unsuitable (>80). Residual Sodium Bi-carbonate: The concentration of bicarbonate and carbonate influences the stability of water for irrigation. High RSBC causes high pH. Fertility of land may be degraded with irrigation water containing high RSBC. Based on Residual Sodium Bi-carbonate (RSBC), the water was classified for suitability of irrigation as satisfactory (<5), marginal (5-10) and unsatisfactory (>10. Total Hardness: Water has classified for hardness according to the ranges recommended by the United States Geological Survey (USGS) and it is soft (0-50), slightly hard (51-100), moderately hard (100-200) and very hard (201-500).