Dissolved nitrous oxide in subsurface drainage under stacking split nitrogen management and cereal rye cover cropping

Indirect greenhouse gas emissions are a major source of uncertainty in global inventories. The contribution of dissolved N2O (dN2O) to indirect emissions is poorly understood, especially considering losses of dissolved gases that stem from subsurface agricultural drainage in nitrogen (N)-intensive corn (Zea mays L.) systems. To better quantify the impacts of recommended management on drainage losses of nitrate (NO3-) and dissolved gases, water quality was monitored during the growing season at replicated drainage plots in Illinois, USA. Four treatments were tested: pre-plant N application (224 kg N/ha with 60 % fall + 40 % preplant); split-N application (224 kg N/ha with 40 % preplant + 60 % side-dress); split-N + cereal rye (Secale cereale L.) cover crop; and 0 N control (n = 4). Dissolved N2O concentrations ranged from < 8–58 µg dN2O-N/L while dissolved methane was consistently low (<3 µg CH4-C/L). Environmental factors (temperature, drainage hydrology, soil inorganic N status) and N application events influenced dN2O concentrations and losses. Cumulative dN2O and NO3- loads followed the same trend: pre-plant N > split N > split + cover crop > 0 N control. The split N + cover crop treatment had a significant reduction in both NO3- load and dN2O concentration compared to pre-plant N application, highlighting the effectiveness of integrated management practices in reducing N losses to the environment. Split-N alone, while less effective in reducing losses, improved corn yield and agronomic efficiency, achieving the second lowest emissions factor (EF5 g). Future research should explore the long-term impacts of these management practices on cumulative dissolved greenhouse gas emissions to better inform climate-smart strategies.