Subsurface Drainage and Nitrogen Fertilizer Management Affect Fertilizer Fate in Claypan Soils

Sustainable nitrogen (N) fertilizer management practices in the Midwest U.S. strive to optimize crop production while minimizing N gas emission losses and nitrate-N (NO 3 -N) losses in subsurface drainage water. A replicated site in upstate Missouri from 2018 to 2020 investigated the influence of different N fertilizer management practices on nutrient concentrations in drainage water, nitrous oxide (N 2 O) emissions, and ammonia (NH 3 ) volatilization losses in a corn ( Zea mays , 2018, 2020)–soybean ( Glyince max , 2019) rotation. Four N treatments applied to corn included fall anhydrous ammonia with nitrapyrin (fall AA + NI), spring anhydrous ammonia (spring AA), top dressed SuperU and ESN as a 25:75% granular blend (TD urea), and non-treated control (NTC). All treatments were applied to subsurface-drained (SD) and non-drained (ND) replicated plots, except TD urea, which was only applied with SD. Across the years, NO 3 -N concentration in subsurface drainage water was similar for fall AA + NI and spring AA treatments. The NO 3 -N concentration in subsurface drainage water was statistically ( p < 0.0001) lower with TD urea (9.1 mg L −1 ) and NTC (8.9 mg L −1 ) compared to fall AA + NI (14.6 mg L −1 ) and spring AA (13.8 mg L −1 ) in corn growing years. During corn years (2018 and 2020), cumulative N 2 O emissions were significantly ( p < 0.05) higher with spring AA compared to other fertilizer treatments with SD and ND. Reduced corn growth and plant N uptake in 2018 caused greater N 2 O loss with TD urea and spring AA compared to the NTC and fall AA + NI in 2019. Cumulative NH 3 volatilization was ranked as TD urea > spring AA > fall AA + NI. Due to seasonal variability in soil moisture and temperature, gas losses were higher in 2018 compared to 2020. There were no environmental benefits to applying AA in the spring compared to AA + NI in the fall on claypan soils. Fall AA with a nitrification inhibitor is a viable alternative to spring AA, which maintains flexible N application timings for farmers.