Impacts of low-disturbance dairy manure incorporation on ammonia and greenhouse gas fluxes in a corn silage–winter rye cover crop system

Authors: Sherman, Jessica; Young, Eric; JOKELA, WILLIAM; CAVADINI, JASON - UNIVERSITY OF WISCONSIN

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/30/2021
Publication Date: 4/16/2021
Citation: Sherman, J.F., Young, E.O., Jokela, W.E., Cavadini, J. 2021. Impacts of low-disturbance dairy manure incorporation on ammonia and greenhouse gas fluxes in a corn silage–winter rye cover crop system. Journal of Environmental Quality. https://doi.org/10.1002/jeq2.20228.
DOI: https://doi.org/10.1002/jeq2.20228

Interpretive Summary: Manure provides an important source of nutrients for crops on dairy farms, but requires careful management to mitigate potential environmental impacts. Timing and method of manure application influence both the nutrient use efficiency by crops, and the likelihood of nutrient losses to runoff water and/or the atmosphere. Ammonia is an economically important nitrogen (N) component of manure that is subject to rapid loss to air if surface applied (broadcast) without any incorporation. Nitrous oxide is another gaseous loss of N from agricultural soils, and it is a potent greenhouse gas (GHG). Manure application method effects on ammonia and GHG fluxes (nitrous oxide, carbon dioxide and methane) in corn silage systems are not well known. We measured the impacts of traditional (broadcast, broadcast-disk) and low disturbance manure application methods (aerator/band, coulter injection, strip-till, sweep inject) on ammonia, nitrous oxide, methane, and carbon dioxide fluxes for replicated corn silage plots located in central Wisconsin. Compared to the fraction of total N loss as ammonia-N for broadcast (17.8%), both strip tillage (0.07%) and coulter inject (2.3%) substantially mitigated ammonia loss. In contrast, broadcast had lower nitrous oxide losses (2.6% of total N) than low disturbance methods (2.7 to 3.6% of total N) and fertilizer N (4.2%). Our results indicate that trade-offs between greater nitrous oxide and reduced ammonia loss for injected vs. surface applied manure should be considered in relation to other site-specific agronomic and environmental field risks.

Technical Abstract: Ammonia (NH3) and nitrous oxide (N2O) losses from agricultural soils represent an economic loss to farms and contribute to greenhouse gas (GHG) emissions. Few studies have measured impacts of low-disturbance liquid dairy manure application (LDMA) on NH3 and GHG fluxes. We measured NH3, N2O, methane (CH4), and carbon dioxide (CO2) fluxes in a corn silage system under LDMA (aerator/band, coulter injection, strip-till, sweep inject), broadcast application, broadcast-disk, and a spring applied urea (134 kg N/ha) treatment in central Wisconsin. Whereas broadcast application resulted in losses of 17.8% of applied total N (TN) as NH3-N, strip-till and coulter inject lost 0.07 and 2.3%, respectively. Mean N2O losses ranged from 2.7 to 3.6% of applied TN for LDMA and were greater for incorporated urea (4.2%) compared to broadcast (2.6%). Manure treatments had numerically greater CO2 fluxes compared to fertilizer. Methane fluxes appeared to be more tied to seasonal temperature and soil moisture changes and not manure application method. Results indicate that LDMA with injection decreased NH3 losses, but increased N2O fluxes compared to broadcast. Trade-offs between greater nitrous oxide and reduced ammonia loss for injected vs. surface applied manure should be explicitly recognized and assessed relative to other site-specific water quality and agronomic considerations.