Effects of green onion (Allium fistulosum) cropping on topsoil nitrogen species contents in a Páramo ecosystem

Páramos are unique ecosystems vital for biodiversity conservation and water supply. However, land-use change has increased reactive nitrogen (N) concentration, leading to environmental pollution. Despite their importance, limited research has been conducted on their soil N pools, which are crucial for regulating N losses and supporting ecosystem services. Therefore, this study analyzed the influence of green onion (Allium fistulosum) cropping on soil N pools and their controlling factors in a Colombian páramo. We collected topsoil (0–20 cm) samples from 50 plots located in cultivated and non-cultivated land. The samples were analyzed for total N (TN), nitrate‑nitrogen (N-NO₃⁻), ammonium‑nitrogen (N-NH₄⁺), and other 13 physicochemical edaphic properties. Cultivated soils exhibited 40 % lower TN and nearly eight times higher N-NO₃⁻ concentrations compared to non-cultivated soils, while N-NH₄⁺ remained relatively stable. TN depletion was linked to SOM loss driven by farming practices, including fresh chicken manure fertilization, burning, and ploughing. Agricultural management practices neutralized soil acidity, favoring nitrification and increasing the risk of N-NO₃ losses via leaching or runoff. Key edaphic properties influencing soil N pools included pH, soil organic carbon, electrical conductivity, available potassium, available sulfur, available phosphorus, soil water content, and bulk density. These findings highlight the need to incorporate these factors into models of soil N dynamics in páramos to better assess the impact of agricultural management on ecosystem functions. Our results provide valuable insights for promoting sustainable N management in sensitive páramo ecosystems.