Greenhouse gas emissions from an irrigated cropping rotation with dairy manure utilization in a semiarid climate

Authors: Dungan, Robert - Rob; Leytem, April; Tarkalson, David

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2021
Publication Date: 3/3/2021
Citation: Dungan, R.S., Leytem, A.B., Tarkalson, D.D. 2021. Greenhouse gas emissions from an irrigated cropping rotation with dairy manure utilization in a semiarid climate. Agronomy Journal. 113(2):1222-1237. https://doi.org/10.1002/agj2.20599.
DOI: https://doi.org/10.1002/agj2.20599

Interpretive Summary: Dairy manure is commonly applied to agricultural soils to increase the nutrient status and improve soil health; however, it is also often associated with the increased emission of trace gases that contribute to global climate change. This study took place in southern Idaho under a typical dairy forage rotation of alfalfa, corn and barley, where manure was applied in the fall or spring. The main objectives of this study were to determine the influence of the manure treatments (compared to no fertilizer and conventional fertilizer treatments), as well as field and crop management practices, on the emission of nitrous oxide, methane, and carbon dioxide over a 3-year period during the growing seasons only. The fall and spring manure treatments produced the great nitrous oxide emissions, while there were no treatment effects on methane and carbon dioxide emissions. Nitrous oxide has a global warming potential (GWP) that is about 300 times greater than that of carbon dioxide, thus it is generally of most interest in studies such as this. The manure applications, however, were also found to substantially increase the the amount of soil organic carbon (SOC) over the study period so that it offset the GWP enough that it was negative. Increasing the amount of SOC in soil is a positive benefit since it is associated with improved soil chemical, physical and biological properties and it can reduce agricultural impacts on global climate change. Manure utilization in cropping systems should be encouraged, as long as it is applied at recommended agronomic rates to prevent nutrient pollution in the environment.

Technical Abstract: Greenhouse gas (GHG) emissions data from irrigated cropping systems utilizing dairy manure are needed in semiarid western regions. The objectives of this field study were to (i) determine the effect of synthetic N fertilizer (urea), enhanced-efficiency synthetic fertilizer (SuperU), composted dairy manure, dairy manure applications (fall and spring applied), and a control (no fertilizer or manure) on GHG losses over the growing season and overall global warming potential (GWP) and (ii) evaluate the influence of irrigation and field/crop management practices on GHG fluxes. The treatments were not applied to alfalfa (2017) but were applied to corn (2018; except SuperU) and barley (2019). Cumulative N2O-N losses over the 3-year rotation ranged from 2.8 to 5.2 kg/ha, with the fall and spring manure losing the greatest amounts of N2O-N. Emission factors indicated that -1.5 to 0.79% of the total N applied was lost as N2O-N during the growing seasons. Cumulative losses of CO2-C and CH4-C over the rotation were on average 12,170 and -0.77 kg/ha, respectively, with no significant differences among the treatments. Major N2O-N pulses were associated with early-season irrigation events and incorporation of fertilizer and manure, but overall fluxes tended to increase during the summer months when soil temperatures were highest. When accounting for increases in soil organic carbon (SOC) over the three growing seasons, the net GWPs were determined to be negative for the compost (-35.4), fall manure (-130.4), and spring manure (-48.9) treatments. As a result, these manure treatments should be considered as an alternative to synthetic N fertilizer use in southern Idaho due to their ability to increase SOC and help reduce agricultural climate impacts, while maintaining high crop yields.