Water Suitability for Paddy Field Irrigation in Tropical Watershed Dominated by Ancient Volcanic Rocks and Limestones, Indonesia

Proper water quality for plant growth is important to ensure high productivity in food production. However, the hydrological and geological characteristics of a region cause distinctive characteristics that need to be understood in order to carry out proper agricultural practices. The purpose of this study was to determine the temporal variation of Tesih River water suitability for irrigation. This research is expected to provide an overview of the temporal variation of water suitability for irrigation in a watershed dominated by ancient volcanic rocks and limestone that have formed karst areas. On the other hand, this study is expected to provide an overview of the influence of climatological conditions controlled by tropical climate and the characteristics of the Asian-Australian monsoon winds at the study site that are strong on water suitability for irrigation. Methods used: Percent Sodium (Na%), Sodium Adsorption Ratio (SAR), Wilcox diagram, USSL diagram, Hardness (H), Magnesium Hazard (MH), Kelly's ratio (KR), Permeability Index (PI), and Residual Sodium Carbonate (RSC). The water suitability methods used were percentage of sodium (Na%), sodium adsorption ratio (SAR), Wilcox diagram, USSL diagram, hardness (H), magnesium hazard (MH), Kelly's ratio (KR), permeability index (PI), and residual sodium carbonate (RSC). The analyses showed that the river water was good (based on Na%, USSL diagram, and RSC), very good (SAR and PI), excellent (the Wilcox diagram), or suitable for irrigation (H, MH, and KR). Overall, the river has the physical and chemical qualities suitable for supporting crop growth without damaging soil properties.