Reduction of mineral fertilizer use through municipal solid waste compost application in potted spinach ( Spinacia oleracea L.)

Abstract The overuse of mineral fertilizers can harm the environment and reduce crops quality. The combined use of N fertilizers with organic amendments may provide a more sustainable fertilization strategy. This study aimed to evaluate the effects of source‐separated organic fraction of municipal solid waste (OFMSW) compost application on crop yield and soil physicochemical properties in potted spinach. Four compost doses (10.38 t ha −1 [T1]; 20.75 t ha −1 [T2]; 30.19 t ha −1 [T3]; and 41.51 t ha −1 [T4]) combined with reduced mineral N fertilization (0.63 g N pot −1 ) were compared with a full mineral fertilization treatment receiving 1.25 g N pot −1 (M) and an unfertilized control (C). Chlorophyll content (measured as SPAD [Soil Plant Analysis Development] Index) and soil electrical conductivity (EC) were monitored over time; moreover, pH, EC, organic matter, and nitrate content were measured before and after harvest. Yield and plant growth response (leaf area, petiole, and leaf blade dry matter percentage) were analyzed after harvest. Treatment T4 showed the highest yield values (146.7 g FW pot −1 ) and soil organic matter content accumulation (1.69%), outperforming the full mineral fertilization treatment. EC values remained below soil spinach salinity tolerance thresholds, without any salt stress symptoms. The highest EC value was 0.62 mS cm −1 , measured in T4 at 21 days after transplant. The lowest compost dose produced a yield comparable to that of full mineral fertilization (M), while reducing mineral N input by 50%. The results support the application of high doses (≥40 t ha −1 ) of OFMSW compost in spinach, with a significant reduction of mineral N fertilizer input. In this crop, the combined use of OFMSW compost and reduced mineral N fertilization may represent an advantageous farming practice from an environmental and economic point of view.