Role of multiple cropping in the conservation of soil fertility and in the reduction of greenhouse gas emissions

The conservation of soil fertility is a pressing challenge in modern agriculture, particularly in the context of climate change and soil degradation. Intensive farming practices have contributed to declining soil organic matter and increased vulnerability to extreme weather events. Addressing these issues requires the adoption of sustainable management practices that enhance soil health, improve nutrient cycling, and promote climate resilience. Multiple cropping systems, especially those integrating cover crops, represent a promising solution, as they improve soil structure, increase organic carbon sequestration, and reduce nutrient losses. However, the effectiveness of these strategies depends on factors such as species selection, management practices, and site-specific conditions. This Ph.D. research investigated the role of multiple cropping systems, with a focus on cover crops, in enhancing soil health, sustaining crop productivity, and mitigating environmental impacts. Two field experiments were conducted in contrasting agroecosystems, a conventional cereal-based system and a lawn-managed system, to evaluate the effects of cover crops and other soil-enhancing strategies on soil chemical, biological, and physical properties as well as crop performance. The first experiment assessed the performance of different cover crops in a lawn-managed system, comparing various clover species and mixtures against a clover monoculture. Particular attention was paid to their effects on soil organic carbon (SOC) dynamics, carbon sequestration, biomass production, and soil water retention. Results demonstrated that species selection strongly influenced soil health outcomes. Crimson clover (Trifolium incarnatum L.) achieved the highest aboveground biomass, while tillage radish, despite lower aboveground biomass, significantly improved SOC fractions, soil water storage, and annual carbon sequestration (4.58 t CO₂ ha⁻¹ y⁻¹). The tap-root system of tillage radish (Raphanus sativus Var.Longpinnatus L.H.Bailey) enhanced soil porosity and introduced root-derived carbon inputs, delivering multifunctional benefits. In contrast, grass-based or mixed-species treatments showed variable effects, and in some cases even resulted in net carbon loss, suggesting that a single growing season may not be sufficient for measurable improvements in soil function. Following these findings, tillage radish was further evaluated in a conventional cereal-based cropping system under contrasting tillage regimes. Tillage radish performed more effectively under conventional tillage, where increased soil disturbance favored root development, biomass production, and nutrient mobilization. Improvements were recorded in SOC, labile carbon fractions, microbial biomass, and nutrient availability, particularly in deeper soil layers. Under reduced tillage, however, plant growth was consistently limited, particularly in drier conditions, likely due to restricted root penetration and slower mineralization of organic matter. Seasonal was also important: wetter periods enhanced shoot growth and nutrient uptake, while drier periods promoted root allocation. A broader multi-site analysis confirmed that tillage radish effectiveness is highly site-dependent. Soil texture, salinity, compaction, and climatic conditions significantly influenced biomass production and nutrient uptake. In finer-textured, low-salinity soils with favorable rainfall patterns, tillage radish showed greater biomass accumulation and nutrient translocation. Across sites, tillage radish increased labile carbon fractions (ΔPOM-C, ΔPOX-C) and microbial biomass pools (ΔMBC, ΔMBP, ΔMBN), particularly where biomass thresholds were met. However, in heavier soils and under biomass-limited conditions, soil improvements were constrained, reinforcing the need for effective residue management. Tillage radish also demonstrated a dual role in nitrogen dynamics, enhancing nitrogen retention and microbial nitrogen accumulation while posing nitrate leaching risks under heavy rainfall or poor residue management. This highlights the need for carefully tailored management strategies to maximize benefits while minimizing environmental risks. To complement these findings, an additional study assessed the integration of sustainable practices, including cover cropping, reduced tillage, crop rotation, and alley cropping, on soil and crop performance in Mediterranean cereal systems. When sown between crop cycles, tillage radish improved the grain and protein yields of spring barley, likely due to enhanced nutrient availability and improved soil structure. While conventional tillage initially led to higher yields, reduced tillage offered greater resilience under waterlogged conditions, suggesting long-term soil structural benefits. At the system level, crop rotations and olive-based alley cropping maintained productivity while improving nitrogen use efficiency and soil quality. In contrast, hazelnut-based alley cropping reduced herbaceous crop yields due to competition, although legume inclusion partially mitigates this effect. Overall, this research confirms the multifunctional role of tillage radish in conservation agriculture, particularly in enhancing soil fertility, promoting carbon sequestration, and improving nutrient cycling. Species selection, pedoclimatic conditions, and tailored management practices emerged as critical factors for maximizing benefits. These findings contribute robust, field-based evidence supporting the integration of multiple cropping systems and soil-improving practices in sustainable agriculture strategies aligned with the goals of the Common Agricultural Policy (CAP 2023–2027).