Water requirement patterns and water management strategies of Bingtang sweet orange (Citrus sinensis Osbeck) in Hunan Province, China

• Stem sap flow in Bingtang sweet orange is primarily regulated by air temperature and soil moisture. • The annual water requirement of Bingtang sweet orange is approximately 1086 mm, of which the fruit enlargement stage accounts for about 34%. • The full irrigation increases leaf area index and single-fruit weight but leads to a reduction in soluble solids and acid content. • A water management strategy for Bingtang sweet orange in Hunan Province: rely on early rainfall, irrigate at 6 mm/day during fruit enlargement stage and apply deficit irrigationduring ripening stage. This study explored the water requirement patterns and water management strategies of Bingtang sweet orange ( Citrus sinensis Osbeck). Annual monitoring of stem sap flow and environmental factors was carried out under pot cultivation conditions. The water requirement patterns were evaluated under full irrigation (FI) in both pot and ridge cultivation, with rainfall-only serving as control. The results indicated that the water requirements of Bingtang sweet orange were closely associated with air temperature and soil moisture content. Stem sap flow stabilized at temperatures higher than 24°C under sufficient soil moisture; water was preferentially allocated to thick branches under low temperature or water deficit; the fruit enlargement stage had the highest sap flow intensity. The annual water requirement was approximately 1086 mm, 34% of which was consumed during the fruit enlargement stage. FI increased leaf area index (22.8%) and single-fruit weight (38.0–154.8%) but reduced the total soluble solids (15.4–39.2%) and titratable acid content (3.7–19.3%). In Hunan Province, approximately 78% of annual rainfall occurs in February-July, while only approximately 12% occurs during the critical July-September fruit enlargement stage, leading to seasonal drought. A water management strategy was proposed: rely on rainfall in spring shoot, flowering, fruit set and young fruit stages (with short-term drought prevention); apply full irrigation (∼6 mm daily) in fruit enlargement stage; implement regulated deficit irrigation during the maturity stage to improve fruit quality.