Drip fertigation with slurry as a promising tool to reduce nitrogen losses under organic maize

The European Union (EU) actively promotes the adoption of organic farming, in which crop N requirements are satisfied via organic fertilizers, such as slurry. Maize (Zea mays L.) is a key crop for both feed and food production with high N uptake. In this short-term study, we tested fertigation with microfiltered slurry liquid faction for maize fertilization as viable strategy to enhance nitrogen use efficiency (NUE) under organic farming while reducing N losses, via ammonia (NH₃), nitrous oxide (N₂O), and nitrate leaching (NO₃^-). We compared three strategies (i) slurry application through surface broadcast of the liquid fraction before sowing as reference fertilization ("Ante" treatment, or "A"), (ii) slurry application through both pre-sowing broadcast of the liquid fraction and fertigation as side-dressing with the microfiltered liquid fraction ("Ante + Post" treatment, or "A + P"), and (iii) slurry microfiltered liquid fraction application as side dressing via fertigation ("Post" treatment, or "P"). Compared to "A", cumulative N losses were reduced by 38% under "A + P" and 58% under "P". Furthermore, NH₃ volatilization decreased by 43% and 71% under "A + P" and "P", respectively. These treatments also reduced N₂O emissions by 30% and 37%. Nitrate leaching was reduced by 56% in the "P" treatment. Overall, the "P" strategy was the most effective in reducing N losses, while "A + P" tended to increase grain production (12.6 Mg ha^-1) and NUE (38.1 kg grain kg^-1 N supply) compared to "P" (11.0 Mg ha^-1 and 35.5 kg grain kg^-1 N supply). These results were primarily attributed to the improved synchronization between N supply and maize N requirements, emphasizing the risk associated with slurry application before sowing. Although conducted over a short experimental period, our study suggests that drip fertigation with slurries can overcome the potential yield losses of organic systems for crops with high N demand such as maize, while reducing N losses, fulfilling the environmental principles of organic farming and current requirements from EU policies.