Ammoia emissions and corn yield from injected vs. surface-applied liquid-seperated anaerobic digestate

Authors: SIGDEL, SIGDEL - Pennsylvania State University; KARSTEN, HEATHER - Pennsylvania State University; Dell, Curtis; HOOVER, RON - Pennsylvania State University

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/5/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Anaerobic digestion of manures allows production of methane to supply on-farm energy demand. The resulting digestate, like manure, is a value nutrient source for crop production, but a large portion of the nitrogen in the digestate is in a form that can be readily lost to the atmosphere as ammonia when the material is applied on the soil surface in no-till cropping systems. Ammonia emission is both a pathway for the loss of crop available nitrogen and a source of air quality impairment. Shallow disk injection of untreated manures has been shown to greatly reduce ammonia emissions in no-till systems and has the potential to also reduce ammonia emissions following land application of digestate. Six corn silage studies were established on commercial dairy farms across Pennsylvania in 2021–2023 with side-by-side strips comparing injection of digestate with surface application. Ammonia losses were 42% less and corn silage yield was 3.8% higher, on average, with injection. These findings indicate that injecting anaerobically digested manure can reduce ammonia loss, increase corn silage yields and returns on investment, and offer environmental benefits by reducing harmful ammonia emissions.

Technical Abstract: 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 concentration (TAN) 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 hours after application, ii) in-season soil nitrate-N, iii) cornstalk nitrate status at harvest, iv) corn silage production, and iv) returns on investment. Surface applied liquid digestate lost twice as much NH3 as injected digestate during the first six hours after application and 58% more cumulative NH3 loss over 24-hours 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, increase corn silage yields and returns on investment, and offer environmental benefits by reducing harmful NH3 emissions.