Soil Compaction: Implications for Greenhouse Gas Emissions and Water Quality in an Italian Cambisol

Soil compaction can significantly affect nutrient dynamics, leading to an increased risk for air and water pollution, reduced crop yield, and lower nitrogen use efficiency. Conservation agriculture and anerobic digestate application are proposed methods to mitigate environmental impacts, yet conservation agriculture may exacerbate soil compaction. Limited research has explored how varying soil compaction depths interact with different cultivation systems and anaerobic digestate fertilization. Furthermore, the impact of soil compaction on nutrient leaching and greenhouse gas emissions remains poorly understood. This study, conducted in Northeastern Italy, aimed to address these knowledge gaps using 20 lysimeters to represent five cultivation systems: bare soil (BS), conventional practices (CV), conventional practices + cover crop (CC), conservation agriculture with shallow (0-25 cm, CA1), and deep compaction (25-45 cm, CA2). Each treatment had four replicates. Sorghum was cultivated in 2023, followed by ryegrass as the cover crop where necessary. Solid digestate (300 kg N ha-1) from mixed agricultural waste was applied as fertilizer. GHG emissions (CO2, N2O, and CH4) were continuously measured using a non-steady state through-flow chamber system coupled with an FTIR gas analyzer, capturing six to eight fluxes per day for each chamber. Volumetric water content was continuously monitored at depths of 15, 30, 60 cm using Time Domain Reflectometry (TDR) sensors and soil temperature were continuously monitored in the 0-30 cm soil profile using thermocouples. Soil samples at depths of 0-5 cm and 5-15 cm were taken for three weeks following fertilization, totaling 280 samples, and analyzed for NH4+-N and NO3--N. Additionally, 208 percolation water samples were collected and analyzed for these same nutrients. Results indicated that sorghum grain yield was higher in non-compacted treatments (5.3 Mg ha-1) compared to compacted treatments (4.5 Mg ha-1). The NUE was generally low, with the highest observed in CV and CC (0.20) and the lowest in CA2 (0.13). Cumulative CO2-C emissions were highest under CV, with 20899 kg ha-1 recorded. N2O emissions peaked in the three weeks following fertilization, reaching 208 g N2O-N ha-1d-1 under CC, while CA2 had lower emissions (53 g ha-1). Soils generally acted as a sink for CH4-C, and absorption was reduced in compacted treatments. Compaction generally increased capillary rise and decreases percolation. Permanent soil cover (CA1, CA2, and CC) reduced nitrate leaching. This suggests that maintaining crop residues and implementing cover cropping, combined with solid digestate application, can mitigate nutrient leaching, preserve soil water content, and minimize percolation losses.