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Greenhouse Gas Emissions from an Irrigated Crop Rotation Utilizing Dairy Manure

A. B. Leytem, A. D. Moore, R. S. Dungan
Soil Science Society of America journal 2019 v.83 no.1 pp. 137-152
application rate, carbon, climatic factors, crop rotation, dairy manure, emissions factor, fertilizer application, fertilizers, global warming potential, greenhouse gas emissions, greenhouse gases, inventories, irrigated farming, manure spreading, soil water, sprinkler irrigation, temperature
Core Ideas Manure addition enhanced N₂O losses. 0.13 to 0.24% of total N added was lost as N₂O. Overall, global warming potential was lower in manure treatments than in fertilizer treatments. Information on greenhouse gas (GHG) emissions from manure application in cropping systems of the irrigated mountain west region is needed. The objectives of this study were to (i) determine the effect of manure application rate and frequency (annual vs. biennial) on GHG losses compared to synthetic fertilizer, (ii) determine the effect of irrigation on GHG losses and (iii) determine the overall global warming potential (GWP) of using manure vs. synthetic fertilizer. Treatments included dry manure rates of 18 or 52 Mg ha⁻¹ applied annually or 36 Mg ha⁻¹ applied biennially as well as synthetic fertilizer and control treatments. Cumulative losses of N₂O‐N over the rotation ranged from 1.4 to 8.4 kg ha⁻¹ with the 52 Mg ha⁻¹ manure application losing the greatest amount of N₂O‐N. Emission factors for the growing season indicated that 0.13 to 0.24% of total N applied was lost as N₂O‐N. Cumulative CO₂–C losses were greatest in the manure treatments, with approximately 7% of carbon added lost as CO₂–C. Maximum N₂O‐N fluxes occurred at soil moisture contents of 0.3 to 0.4 m³ m⁻³ and temperature near 25°C, while CO₂–C emissions occurred over broader soil moisture and temperature conditions. The overall GWP associated with manure application indicated a net negative GWP for manure treatments while the synthetic fertilizer treatment was near neutral. Including manure in cropping system rotations can lead to enhanced GHG emission, however the benefits of enhanced SOC can outweigh these losses leading to lower GWP than use of synthetic fertilizer alone.