Balancing yield, water productivity, and fruit quality of processing tomatoes through the combined use of biodegradable mulch film and regulated deficit irrigation

Italy is the third largest producer of processing tomatoes (Solanum lycopersicum L.) worldwide. Tomato production is projected to be considerably affected by climate change, especially in drought-prone regions where maximizing water use efficiency is essential. A two-year on-farm experiment was conducted to compare full irrigation (T1) with two water-saving irrigation strategies: T2 (regulated deficit irrigation, RDI) and T3 (RDI combined with soil-biodegradable mulch film). The experiment was conducted at two representative sites in southern Italy, where yield performance, sustainability, and fruit quality were assessed. T2 resulted in 31 % water savings and maintained comparable yields, increasing irrigation (+44 %) and economic (+56 %) water productivities with respect to T1. Nevertheless, the accelerated crop cycle observed in T2 reduced the leaf coverage of fruit, leading to a higher number of sun-scalded fruits and decreased lycopene content at harvest. The negative effects of RDI were partially mitigated by combining it with soil-biodegradable mulch film (T3), which improved the soluble solid content (+4 %), marketable (+23 %) and Brix (+28 %) yields, and irrigation (+71 %) and economic (+78 %) water productivities compared with T1. Metabolic profiling further highlighted that T3 increased key stress-related metabolites, including alanine (+50 %), glycine (+31 %), and proline (+44 %), indicating enhanced metabolic adaptation to water stress. The increase in proline, a crucial osmolyte and antioxidant, suggests improved nitrogen use efficiency and overall metabolic resilience under water-deficient conditions. Based on these findings, T3 is recommended as a valuable practice for improving yield and sustainability, while maintaining fruit quality in drought-prone areas.