Ammonia emissions and corn yield response from injected versus surface-applied liquid-separated anaerobic digestate

Anaerobic digestion and digestate solid–liquid separation are manure treatment strategies used on commercial dairy farms. These treatment strategies typically result in increased total ammoniacal nitrogen (TAN) concentration and pH, and reduced dry matter content, which tend to increase ammonia (NH₃) emissions following field application. We hypothesized that shallow-disk injection of liquid-separated, anaerobically digested dairy manures, compared to surface application without incorporation on no-till farmland, would reduce NH₃-N emissions and conserve manure-N for crop production. Six corn (Zea mays L.) silage studies were established on commercial dairy farms across Pennsylvania in 2021–2023 with side-by-side field-scale treatment comparison strips replicated five times per farm. We quantified the impact of liquid-separated, anaerobically digested manure application methods on (i) NH₃ emissions for 24 h after application, (ii) in-season soil nitrate-N, (iii) cornstalk nitrate at harvest, (iv) corn silage production, and (v) returns on investment. Surface-applied liquid digestate lost twice as much NH₃ as injected digestate during the first 6 h after application and 58% more cumulative NH₃ loss over 24 h after application. Pre-sidedress soil nitrate-N test and corn stalk nitrate at harvest indicated there was more than sufficient N for corn with both treatments. Across farms, corn silage yield was 3.8% greater (p < 0.05) with injection than surface broadcast and returns on investment were greater in five of the six comparisons. These findings indicate that injecting liquid-separated anaerobically digested manure can reduce NH₃ loss, slightly increase corn silage yields and returns on investment, and offer environmental benefits by reducing harmful NH₃ emissions.