Growing and non-growing season nitrous oxide emissions from a manured semiarid cropland soil under irrigation

Authors: Dungan, Robert - Rob; Leytem, April; MOORE, AMBER - Oregon State University; Bjorneberg, David - Dave; GRACE, PETER - Queensland University Of Technology; BRUNK, CHRISTIAN - Queensland University Of Technology; ROWLINGS, DAVID - Queensland University Of Technology

Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/13/2023
Publication Date: 6/1/2023
Citation: Dungan, R.S., Leytem, A.B., Moore, A., Bjorneberg, D.L., Grace, P., Brunk, C., Rowlings, D. 2023. Growing and non-growing season nitrous oxide emissions from a manured semiarid cropland soil under irrigation. Agriculture, Ecosystems and Environment. 348:108413. https://doi.org/10.1016/j.agee.2023.108413.
DOI: https://doi.org/10.1016/j.agee.2023.108413

Interpretive Summary: Dairy manure is commonly applied to croplands to improve soil fertility, but this generally results in increased emissions of nitrous oxide (N2O), which is a powerful greenhouse gas. The measurement of N2O emissions is usually conducted during the warmer growing season, while emissions during the colder non-growing season are often not measured and are assumed to be dramatically lower. The objective of this study was to measure N2O fluxes during the growing and non-growing seasons in 2020 (sugar beet) and 2021 (corn silage) in a semiarid irrigated field that received inorganic N fertilizer or was previously treated with dairy manure solids at 3 different application rates for 8 years. The N2O emissions were found to be highly episodic and major pulses were associated with freeze-thaw events in the winter, irrigation events during the growing season, and soil disturbance at harvest. Nitrous oxide emissions were greatest from soil that had received manure at the highest application rate, with cumulative emissions being 3-fold greater than plots treated with inorganic fertilizer or manure at lower application rates. When breaking down the annual cumulative emissions by season, approximately 50% occurred during the non-growing season, regardless of fertilizer treatment. Our results stress the need to measure N2O emissions during the non-growing season as a way to improve the accuracy of annual emission estimates. Proper accounting of emissions is critical to ensure greenhouse gas inventories for agriculture are accurate.

Technical Abstract: Dairy manure is used in semiarid southern Idaho to improve soil fertility, but campaigns to measure resulting nitrous oxide (N2O) emissions over the complete year have not been conducted to date. The objective of this study was to measure N2O fluxes throughout the growing and non-growing seasons in 2020 (sugar beet) and 2021 (corn silage) in a field that received inorganic N fertilizer or was previously treated with dairy manure solids on an annual and biennial basis for 8 years. Gas fluxes were measured daily using automated chambers that were connected to a gas chromatograph for in situ analysis of N2O. The N2O emissions were found to be highly episodic and major pulses were associated with freeze-thaw events in the winter, irrigation events during the growing season, and soil disturbance at harvest. Emissions were greatest from soil that had received manure at the highest annual application rate of 52 Mg/ha (dry wt.), with cumulative totals of 3.6 and 3.0 kg N2O-N/ha in 2020 and 2021, respectively. These cumulative totals were about 3-fold greater than emissions from plots treated with inorganic fertilizer or manure at 17 Mg/ha annually or 35 Mg/ha biennially. This outcome can be attributed to high concentrations of nitrate produced through mineralization of organic N in manure. Emission factors indicated that 0.6 to 0.9% of the total N applied was lost as N2O-N over the two years. When breaking down the emissions by season, anywhere from 49 to 63% (2020) and 37 to 58% (2021) of the N2O-N emissions occurred during the non-growing season. Cumulative growing and non-growing season N2O emissions were found to be statistically equivalent in the inorganic fertilizer and manure treatments. This finding stresses the need to also measure N2O emissions during the non-growing season as a way to improve the accuracy of annual emission estimates.