Seasonal leachate organic carbon and total nitrogen in an organic integrated crop–livestock rotation system

Abstract Integrated crop–livestock systems (ICLS) can reduce nutrient losses relative to annual cropping, yet seasonal dynamics of dissolved organic carbon (DOC) and nitrogen in organic systems remain poorly understood. We evaluated non‐purgeable organic carbon (NPOC), total nitrogen (TN), and C:N ratios during the sixth and seventh years of a certified organic ICLS in Kentucky. Subsurface soil water samples were collected at 1‐meter depth across seven treatments, including three rotational goat‐grazed pasture phases, two cropped phases, ungrazed perennial pasture (PP), and a continuous corn–soybean system (CNP). NPOC showed strong seasonality, with low spring concentrations and pronounced autumn increases, indicating dominant hydrologic control over DOC exports. In contrast, TN varied with season and management, with elevated concentrations during crop‐to‐pasture transitions and in CNP. Mature grazed pasture phases and PP generally maintained lower TN and higher C:N ratios, indicating enhanced nitrogen retention. Rotational transitions represent critical periods of nitrogen leaching risk. Core Ideas Soil water non–purgeable organic carbon was driven mainly by sampling season. Total nitrogen varied more with rotation phase and management. Early pasture estlablishment increased nitrogen leaching risk. Continuous corn–soybean cropping had greater nitrogen leaching risk. Mature pasture phases improved nitrogen retention in organic integrated crop–livestock systems.