Drainage volume drives dissolved organic matter leaching loss in a corn system

Leaching loss of dissolved organic matter (DOM) in terrestrial systems has gained increasing attention due to its critical role in carbon (C) translocation. While existing studies on DOM composition and dissolved organic carbon (DOC) leaching primarily focus on wetland and forest soils, environmental and management drivers of DOM leaching dynamics in subtropical row-crop systems remain less understood. To address this gap, we used lysimeter observations from a nitrogen (N) rate experiment in a Florida corn system over two years to assess DOM leaching loss and composition. The cumulative loss of DOC varied between 9.74 and 27.56 kg ha^-1 across two growing seasons and a cover crop season. Hurricane Debby induced an extreme DOC loss of 16.92 kg ha^-1 and total N (TN) loss of 298.97 kg ha^-1 within days. In the 2024 growing season, groundwater likely intruded our lysimeters, introducing additional TN but diluting DOC content. In each season, DOC loss was linearly correlated with drainage volume. The strength of this relationship varied by seasons, influenced by temporal coupling of DOC supplies and drainage flux. In contrast, DOC concentration and composition did not consistently correlate with drainage volume but instead showed seasonal patterns linked to key events. For example, during the vegetative stage of corn, DOM composition shifted to more protein-like, microbially associated compounds. After soil disking and stalk return, as well as following the hurricane, DOC composition shifted toward more aromatic compounds. The DOC and TN leaching loss and DOM composition did not show a consistent difference between control and fertilized treatments. In conclusion, our results suggest that DOC leaching is mainly driven by drainage volume in this subtropical agroecosystem, while seasonal shifts in DOM composition reflected changes in DOC sources. Our findings also highlight the importance of hurricanes and groundwater intrusion in regulating DOM and TN dynamics.