Deficit Irrigation Strategies (DI and PRD) Effects on Potato (Solanum Tuberosum L.) Yield, Nitrogen Nutrition, NUE and IWUE under Tunisian Semi-arid Conditions.

A reasonable supply of water and nitrogen is a key success factor in potato crop production. Excess or deficiency of these two elements has direct negative impacts on final yield and product quality. In arid and semi-arid regions, the adoption of water deficit irrigation strategies at the farm level is now an obligation to overcome water scarcity and optimise crop yields. The use of such deficit irrigation strategies also requires studying their impact on crop nitrogen nutrition and use. This work aims to study the impact of deficit irrigation strategies (DI and PRD) on potato nitrogen nutrition and use under specific climate and soil conditions in Tunisia. To achieve this objective, a two-year field trial was set up in 2021 and 2022. The experimental protocol is a complete randomised block design with three irrigation regimes: 1- Full Irrigation (FI) receiving 100% of the crop evapotranspiration (ETc), 2- Deficit Irrigation (DI₇₅) with 75% of the ETc, and 3- Partial Root Zone Drying (PRD₅₀) with 50% of the ETc. Our results showed that the PRD₅₀ slightly decreased potato yield, but not significantly compared to FI and DI₇₅. SPAD-502 values were lower with the PRD regime than with FI and DI75 at 72 and 83 DAP, but the differences were not statistically significant. The total nitrogen content of the plant was significantly affected by the irrigation regime at 70 and 100 DAP. FI had the highest N content, followed by PRD₅₀ and DI₇₅. The Nitrogen Nutrition Index (NNI) was also significantly affected by the irrigation regime, with the FI treatment yielding the highest values, while DI₇₅ and PRD₅₀ induced nitrogen stress at 100 DAP. NUE decreased slightly with the PRD₅₀ regime, but not significantly, while PRD50 and DI75 significantly increased IWUE compared to FI.