Assessment of Surface Water Quality for Irrigation from Six Different Districts in Bhutan

Irrigation water plays a vital role in increasing crop productivity. But due to the scarcity of water large areas of farmlands were left fellow in Bhutan. Hence, the government initiated numerous irrigation projects making surface water available for cultivation. However, it was also felt important to analyse these waters for their concentration of dissolved salts. Hence, this study was conducted to assess the quality of the waters used in different regions of the country. Thus, water samples were collected from 11 sampling sites in April 2021 to August 2023. A total of 99 water samples were analysed to estimate the levels of salinity, SAR, %N, Kelly’s ratio and MAR. The results were compared for their suitability with the USSL guideline for classification. It was found that the salinity results ranged from 20 – 110 micromhos/cm corresponding to the salinity Class C1. Similarly, the range of water results for SAR displayed 0.01 – 1.14 corresponding to Class S1 in the USSL diagram. Both the salinity and SAR values demonstrated all the water sources are within the Class C1-S1 indicating their suitability. However, some MAR values were very high exceeding the permissible limit of 50% demanding further investigation.