Can manure application method and timing with cover crops reduce NH3 and N2O gas losses and sustain corn yield?

Ammonia (NH₃) loss following manure application is an environmental concern and N loss for crop production. Manure injection typically reduces NH₃ loss compared to surface application without incorporation but increases emissions of nitrous oxide (N₂O), which is a potent greenhouse gas. Synchronizing manure in spring with cover crop (CC) growth may increase N recovery and reduce N₂O emissions compared to applying manure later in the absence of growing crops. We compared the two following manure application methods: shallow-disk injection (IM) or surface banding without incorporation (BM) to annual ryegrass (Lolium multiflorum L.) and red clover (Trifolium pratense L.) CC at two times: early spring on growing CC (EARLY) and late spring on terminated CC (LATE). The randomized split-plot block experiment was conducted at Rock Springs, PA, during 2021–2022. After manure application, we measured NH₃ for 72 h and N₂O throughout the growing season. Aboveground CC biomass, N, and C:N ratio; pre-sidedress soil nitrate; corn (Zea mays L.) stalk nitrate; and silage yield were assessed. Averaged across application times, compared to BM, IM reduced cumulative NH₃ loss, increased soil N, and resulted in 13% greater corn yield but increased yield-scaled N₂O. Compared to BM LATE, BM EARLY reduced NH₃ loss by 43%, increased CC N, reduced N₂O emission by 50%, but decreased corn yield by 11%. When IM was EARLY compared to LATE, CC N increased 84%, cumulative N₂O loss decreased 55%, and corn yield was similar. Injecting manure to growing CCs offers a strategy for reducing detrimental NH₃ and N₂O emissions and maintaining corn yield.