Tidal inundation type and soil chemical properties determine rice productivity in tropical acid sulfate swamp ecosystems

Ensuring sustainable rice (Oryza sativa L.) production in tidal swamp ecosystems is critical for strengthening food security in Indonesia.Soil chemical properties, tidal inundation type, and planting season strongly influence rice productivity in these systems.This study evaluated soil chemical characteristics and rice productivity across tidal swamp areas in Tanah Bumbu Regency, South Kalimantan, Indonesia, by inundation type and cropping season.Field surveys, soil analyses, and farmer interviews were conducted in five villages.Selimuran and Mudalang were classified as Type B tidal swamps.In contrast, Rantau Panjang, Api-api, and Segumbang were categorized as Type C. Type B soils were acidic, while Type C soils were very acidic.Although both types exhibited low organic C, total N, and exchangeable P, Type B soils had higher P and base cation availability and lower concentrations of exchangeable Al, Fe, sulfate, and pyrite.The pyritic layer was shallower in Type C soils, increasing oxidation risk.Rice productivity was significantly higher in Type B systems (5.43 t ha⁻¹) than in Type C systems (3.76 t ha⁻¹).Seasonal responses differed between tidal types.Yields in Type B fields declined by 0.95 t ha⁻¹ from the dry to the rainy season, whereas yields in Type C fields increased by 0.45 t ha⁻¹.These findings highlight the importance of site-and season-specific nutrient and water management to enhance productivity and sustainability in acid sulfate tidal swamp ecosystems.