The quality and usability of spring water for irrigation (case study: Ngerong Spring, Rengel Karst, Tuban, East Java)

Karst springs have an essential role as sources of drinking water, agriculture, industry, and other domestic needs. This research was conducted on the Ngerong spring as the largest water source for irrigation needs in the Rengel Karst. This study aims to determine the quality and usability of spring water for irrigation by using available data on hydrochemistry. The automatic measurement of water level, conductivity, and temperature parameters was observed at karst spring during sixteen months monitoring period. Furthermore, the water samples were collected every two weeks and more intensive in flood events to analyze major ions. Irrigation quality parameters such as salinity, Sodium Absorption Ratio, Sodium Percentage (Na), Permeability Index (PI), Kelly Ratio (KR), and Magnesium Hazards (MH) were analyzed for the suitability for irrigation. This study revealed that major ion types in the Ngerong Spring are Ca-HCO3 (calcium bicarbonate). The value of irrigation quality parameters showed at excellent to good category, and grouped as C2S1 (medium-low) indicates that spring waters quality is considered well qualified for irrigation.