Optimizing Water Footprint, Productivity, and Sustainability in Southern Italian Olive Groves: The Role of Organic Fertilizers and Irrigation Management

This modeling study evaluates the combined effects of organic fertilization and irrigation regimes on olive productivity and environmental sustainability in southern Italy. Field experiments were conducted in an organic olive grove (cv. Leccino) under Mediterranean conditions, testing four organic fertilization treatments—biochar (BCH), compost (CMP), dried blood (DB), and a commercial organic fertilizer (CTR)—and two irrigation strategies. The CropWat model was employed to simulate additional irrigation scenarios, ranging from full irrigation (Full; 100% ETc) to rainfed conditions. Results showed that biochar-treated olive groves achieved the highest yields (up to 3756 kg ha−1 under full irrigation), outperforming other treatments, with yields of 3191 kg ha−1 (CMP), 2590 kg ha−1 (DB), and 2110 kg ha−1 (CTR). Deficit irrigation strategies, such as ceasing irrigation during the pit-hardening stage (Red_Farm; 1160 m3 ha−1), reduced water use by 67% compared to Full (3600 m3 ha−1) while maintaining satisfactory yields (3070 kg ha−1 vs. 2035 kg ha−1 on average across all fertilization treatments). Water footprint (WFP) analysis revealed that BCH consistently achieved the lowest WFP values (e.g., 1220 m3 t−1 under Full and 687 m3 t−1 under rainfed conditions), outperforming CTR (1605 m3 t−1), CMP (1645 m3 t−1), and DB (1846 m3 t−1) under full irrigation and 810 m3 t−1, 1219 m3 t−1, and 1147 m3 t−1 with no irrigation water supply. Incremental water productivity (IRincr) and marginal water footprint efficiency (WFPincr) further demonstrated that BCH optimized both productivity and environmental sustainability, with IRincr values of 0.55 kg m−3 and WFPincr values of 1.58 m3 kg−1 (averaged for all water regimes), better than CTR (0.40 kg m−3 and 2.14 m3 kg−1), CMP (0.46 kg m−3 and 1.93 m3 kg−1), and DB (0.38 kg m−3 and 2.32 m3 kg−1). An aggregated scoring system, based on standardized and normalized data, ranked BCH under the Red_Farm irrigation strategy as the most effective management approach, achieving the highest overall score compared to the other fertilizer treatments in combination with the different irrigation strategies, thereby balancing high yields with significant water savings.