Introduction of summer cover crops in soft wheat (Triticum aestivum spp. aestivum) monoculture rotation: effects on agronomic traits and soil properties after three years

Context – Continuous wheat systems are common across Mediterranean Europe, yet management strategies that simultaneously sustain yield and improve soil health remain poorly defined. Objective – This study aimed to assess the short-term effects of introducing summer cover crops and different nitrogen rates in a soft wheat monoculture during the system’s initial transition toward a new equilibrium. Methods – A three-year field experiment in northern Italy evaluated the combined effects of summer cover crop species and N fertilization rates on wheat yield, grain protein concentration, nitrogen use efficiency (NUE), and soil organic carbon (SOC) dynamics. Five ground-cover treatments (bare fallow, natural grassing, sorghum, sorghum + cowpea, cowpea + niger) were tested under three nitrogen (N) fertilizer rates (0, 90, 150 kg N ha−¹). Results – Wheat yield and protein were primarily determined by N rate and cover crop residue quality. Legume-based covers (cowpea + niger and sorghum + cowpea) maintained yields comparable to the fertilized fallow at 90 kg N ha−¹, while pure sorghum residue required 150 kg N ha−¹ to partially offset yield reductions associated with its high C/N ratio. Across all years, NUE declined at 150 kg N ha−¹, indicating limited efficiency gains from higher fertilization. Grain protein concentration followed a similar pattern, increasing with N rate but constrained under sorghum cover. Soil analyses showed that cover crops increased total SOC by approximately 6 Mg C ha−¹ compared to fallow, with 74% of the additional C stabilized in the mineral-associated organic matter (MAOM) fraction. SOC gains were greatest under sorghum residues but required higher N inputs to sustain yield and grain quality. Conclusions – These results demonstrate that adjusting N fertilization according to cover crop residue quality is critical to balancing productivity and soil C sequestration in continuous wheat systems. Legume-based summer covers combined with moderate N inputs (90 kg N ha−¹) optimized NUE while maintaining yield and enhancing SOC. Implications – This research provides practical, field-based guidance for integrating cover crops into Mediterranean cereal systems to improve both agronomic performance and soil resource sustainability.