| Summary: | Efforts to reduce greenhouse gas (GHG) emissions from cattle production have led to modifications of livestock diet composition aimed at reducing CH<sub>4</sub> emissions from enteric fermentation. These diet modifications can result in varied manure types that may differentially affect GHG emissions when applied to soil. The purpose of this experiment was to examine the effect of different manure types on GHG emissions. We conducted an incubation experiment, comparing the manure from livestock fed a corn-based diet (CM) to that from livestock fed a traditional barley-based diet (BM). The manures were applied to three soil types (with varied soil fertility and pH) and compared to a control (without manure application). Carbon dioxide (CO<sub>2</sub>) emissions were greater from CM than from BM across all soil types (29.1 and 14.7 mg CO<sub>2</sub>-C kg<sup>−1</sup>, respectively). However, CM resulted in lower N<sub>2</sub>O emissions relative to BM in the low fertility soil (4.21 and 72.67 μg N<sub>2</sub>O-N kg<sup>−1</sup>, respectively) and in lower CH<sub>4</sub> emissions relative to BM in the two acidic soils (0.5 and 2.5 μg CH<sub>4</sub>-C kg<sup>−1</sup>, respectively). Total GHG emissions (sum of CO<sub>2</sub>, N<sub>2</sub>O, and CH<sub>4</sub>) were similar between CM and BM across all soil types, but CM (unlike BM) had 52–66% lower emissions in the low fertility soil relative to both CM and BM in the high fertility soil. Our study shows that manure and soil type interact to affect GHG emissions and that CM may mitigate N<sub>2</sub>O emissions relative to BM when applied to low fertility soils.
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