Impact of management practices on nitrous oxide emissions in an irrigated dairy forage rotation

Authors: Dungan, Robert; Leytem, April; MIITO, GILBERT - University Of Idaho

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/5/2025
Publication Date: 8/6/2025
Citation: Dungan, R.S., Leytem, A.B., Miito, G.J. 2025. Impact of management practices on nitrous oxide emissions in an irrigated dairy forage rotation. Journal of Environmental Quality. https://doi.org/10.1002/jeq2.70063.
DOI: https://doi.org/10.1002/jeq2.70063

Interpretive Summary: The long-term effects of tillage type, winter cover crop, and dairy manure on nitrous oxide (N2O) emissions under continuous silage corn were investigated in a semiarid cropland. Data of this nature is needed to better understand the effect of combined management practices on greenhouse gas emissions, in particular N2O, which has a global warming potential around 265 times that of carbon dioxide. Agriculture is a significant contributor to N2O emissions, with soil management accounting for approximately 74% of all anthropogenic N2O emissions. After six years of treatment, emissions were found to be slightly lower from conventional versus strip tillage in year one of the study. Strip tillage is a type of reduced tillage, that only disturbs the soil where the future plant rows will be located. However, strip tillage does not allow for the incorporation of dairy manure, thus resulting in a manure pack on the soil surface. To deal with the manure pack, we moldboard plowed (i.e., inversion tilled) the entire field, then continued to measure N2O emissions for two more years. After plowing the emissions were generally lower, but they were not significantly different between the two previous tillage types. This suggests that previous tillage does not impart a legacy effect on N2O emissions after moldboard plowing. Regardless, N2O emissions were found to be significantly greater from manured versus non-manured plots. Winter cover crops, which can be used to stabilize reactive nitrogen, were not found to reduce N2O emissions. While manure applications are valuable with respect to increasing soil organic carbon, it does not appear that N2O emissions can be effectively mitigated via strip tillage and cover crops in irrigated silage corn production. Part of this is related to the fact that irrigation enhances N2O emissions due to increased anaerobic conditions in soil.

Technical Abstract: The long-term effect of combined management practices on nitrous oxide (N2O) emissions from semiarid irrigated cropping systems are poorly understood. This study examined the effect of tillage type, winter cover crop, and dairy manure on N2O emissions under continuous silage corn (Zea mays) after 6 years of implementation. The main treatments consisted of conventional tillage [CT] vs reduced tillage [RT], while subtreatments were dairy manure vs synthetic fertilizer and winter triticale (x Triticosecale Wittmack) vs fallow for each tillage type. Solid dairy manure was applied annually each fall (2015-2020), then starting in spring 2021, N2O fluxes were monitored weekly using vented, non-steady-state, closed chambers. The largest N2O fluxes occurred when irrigation commenced during the growing season, with some large fluxes also occuring during wintertime. In 2021, cumulative growing and non-growing season N2O emissions under RT were 25% greater relative to CT [RT, 3.33 kg N2O-N/ha; CT, 2.66 kg N2O-N/ha]. In spring 2022, the entire field was moldboard plowed, resulting in no significant differences in cumulative N2O emissions between the two previous tillage types in 2022 and 2023. Regarding subtreatments, manure produced significantly greater cumulative N2O emissions than synthetic fertilizer, resulting in average increases of 723, 267, and 147% in 2021, 2022, and 2023, respectively. There was no significant effect of winter cover crop on N2O emissions despite the fact that preplant soil nitrate concentrations were reduced by cover crop each year of the study.