Sustainable Use of Organic and Industrial Waste Amendments to Enhance Durum Wheat Productivity and Soil Fertility under Water Scarcity in the Mediterranean Region

Water scarcity severely limits crop productivity in arid and semi-arid regions, highlighting the need for innovative soil management strategies to enhance plant performance and maintain soil health under limited water. However, field-based evidence combining mineral-rich by-products with biodegradable organic amendments remains limited, especially in cereal systems under drought stress. A two-year field experiment (S1 and S2) was conducted using a randomized design with three replicates per treatment, each plot covering 1.2 m². Five treatments were evaluated: Control (T^-), recommended NPK, steel slag (S, 700 kg ha^-1), green waste compost (OA, 4000 kg ha^-1), and their combination (S_OA), under well-watered (100% ETc) and drought stress (30% ETc) conditions. Application rates were previously optimized in greenhouse trials. Compost, derived from plant residues, contained 20% organic carbon, 700 ppm available phosphorus, 1.5% total nitrogen, and 0.5% potassium, while steel slag from a Moroccan steel industry contained 0.37% P₂O₅, 30.6% CaO, and 8% SiO₂. A two-way ANOVA was used to assess treatment effects. Under drought, the combined application (S_OA) significantly improved soil fertility, increasing organic matter (by 183% in S1 and 111% in S2), total nitrogen (by 69% in S1 and 96% in S2), and available phosphorus (by 103% in S1 and 94% in S2) compared with the control. Durum wheat exhibited enhanced drought tolerance, with higher photosynthetic efficiency (+5.13% in 2023 and +4.78% in 2024), relative water content (+24% in S1 and +27% in S2), and grain yield (+68% in S1 and +59% in S2). Grain protein and nitrogen contents increased by 51% and 35% in S1 and 42% and 35% in S2, respectively. Heavy metal analysis in grains showed no significant differences between untreated and treated plants, confirming the environmental safety of the amendment. Nonetheless, further studies are needed to evaluate long-term metal accumulation in soil and economic feasibility at larger scales.