Characterization of agro-well water in Malwathu Oya cascade-I in Anuradhapura district of Sri Lanka

• Published in: Tropical agricultural research Vol. 25; no. 1; pp. 46 - 55
• Main Authors: Kumari, M.K.N., Pathmarajah, S., Dayawansa, N.D.K.
• Format: Journal Article
• Language: English
• Published: Postgraduate Institute of Agriculture, University of Peradeniya 17.09.2015
• Subjects: agro-wells, groundwater potential, irrigation water quality, malwathu oya cascade-i
• ISSN: 1016-1422
• DOI: 10.4038/tar.v25i1.8029

Malwathu Oya cascade is one of the largest and intensively cultivated small tank cascade systems in Anuradhapura district of Sri Lanka. Agro-wells are the most valuable resource for many farmers in this cascade area as these shallow dug wells have a good potential to sustain crop production during the dry season. However, deterioration of groundwater quality during the dry period has been reported in many parts of the dry zone.Therefore, this study focused on the characterization of agro-well water for its suitability for irrigation in the Malwathu Oya cascade based on its quality and availability. Groundwater samples were collected during March to September 2012 to cover the dry period during which the water quality deterioration has been reported in the dry zone. Electrical Conductivity (EC), pH, concentrations of sodium, potassium, magnesium and calcium, and depth of groundwater were measured from 20 selected agro-wells. The residual sodium carbonate (RSC), sodium adsorption ratio (SAR) and sodium percentage (Na %) were calculated using the measured parameters. Based on the depth of groundwater available at the end of dry season, 35%, 25%, 25% and 15% of the wells recorded low, moderate, high and very high groundwater potential, respectively. The EC data showed that 35%, 55% and 10% of the wells had good, doubtful and unsuitable quality of irrigation water, respectively. According to SAR and RSC, all the wells had water good for irrigation. Based on the percentage sodium, 10% of the wells had excellent, 60% had good, 25% had permissible and 5% had doubtful quality irrigation water. According to the US salinity hazard diagram 40% of wells had medium salinity and low sodium hazard. Fifty percent of the samples had high salinity and low sodium hazard while 10 % of the samples had very high salinity and medium sodium hazard. Based on the water quality parameters measured, 25%, 15%, 50% and 10% of the wells in Malwathu Oya cascade fall into good, permissible, doubtful and unsuitable category for irrigation, respectively. Tropical Agricultural Research Vol. 25 (1): 46-55 (2013)