Location: Northwest Irrigation and Soils ResearchTitle: Greenhouse gas emissions from an irrigated crop rotation utilizing dairy manure Author
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2018
Publication Date: 2/21/2019
Citation: Leytem, A.B., Moore, A.D., Dungan, R.S. 2019. Greenhouse gas emissions from an irrigated crop rotation utilizing dairy manure. Soil Science Society of America Journal. 83:137-152. https://doi.org/10.2136/sssaj2018.06.0216.
DOI: https://doi.org/10.2136/sssaj2018.06.0216 Interpretive Summary: Information on greenhouse gas (GHG) emissions from manure application in cropping systems of the irrigated mountain west region is needed. The effects of manure application rate and timing on GHG emissions from a four-year commercial rotation under sprinkler irrigation was investigated. Treatments included dry manure rates of 23 or 8 tons/acre applied annually or 16 tons/acre applied biennially as well as fertilizer and control treatments. At the highest manure application rate, both cumulative nitrous oxide (N2O) and carbon dioxide (CO2) losses increased above that of commercial fertilizer treatments and moderate manure application rates applied either annual or biennially. Fluxes of N2O were greatest when both soil moisture and temperature were high, with a few large spikes in emissions accounting for the majority of growing season N2O losses. Emissions of N2O in the non-growing season were high for the highest manure application rate following the second manure application, suggesting that non-growing season emissions needs to be accounted for when determining annual cumulative emissions. As increasing rates of repeated manure applications had negative impacts on crop yield and in some cases crop quality, emission intensities of the highest manure application rate were greater than those of fertilizer and moderate manure applications. This finding suggests that not only yield but crop quality should be considered when evaluating the effects of manure treatment on emission intensities. Although manure application increased N2O emissions compared to fertilizer, there was a net gain in soil organic carbon offsetting these emissions which led to net negative global warming potential of manure application. Therefore, a more holistic evaluation of manure application in cropping systems should be accounted for in order to determine the overall carbon footprint of these systems. The emission factor for all treatments was less than 0.24%, which is lower than the value currently used by the International Panel on Climate Change (1%), suggesting that development of regional emission factors may be necessary to account for differences in soils and climatic conditions.
Technical Abstract: Information on greenhouse gas (GHG) emissions from manure application in cropping systems of the irrigated mountain west region is needed. The effects of manure application rate and timing on GHG emissions from a four-year commercial rotation under sprinkler irrigation was investigated. Treatments included dry manure rates of 52 or 18 Mg/ha applied annually or 36 Mg/ha applied biennially as well as fertilizer and control treatments. Cumulative losses of N2O-N over the rotation ranged from 1.4 to 8.4 kg/ha with the 52 Mg/ha manure application losing the greatest amount of N2O-N. Calculated emission factors indicated that 0.13 to 0.24% of total N applied was lost as N2O-N, much less than the emission factor of 1% used by the IPCC. Cumulative CO2-C losses were greater in the manure treatments compared to the fertilizer and controls, with approximately 7% of carbon added lost as CO2-C. These soils acted as a sink for CH4-C with average fluxes ranging from -0.1 to -0.3 kg/ha. Maximum N2O-N flux levels occurred at soil moisture contents ranging from 0.3 to 0.4 m3/m3 and temperature near 25 °C, while CO2-C emissions occurred over broader soil moisture and temperature conditions. The overall global warming potential (GWP) associated with manure application indicated that the manure treatments had a net negative GWP while fertilizer treatment was near neutral. A better understanding of regional soil and climatic conditions that affect GHG emissions will enable the development of emission factors more appropriate for use in GHG inventory efforts.