Bacterial Communities and Soil Properties Influencing Dung Decomposition and Gas Emissions Among Japanese Dairy Farms

Dung decomposition on dairy farm soils is an important ecosystem service because it is linked to nutrient recycling in the soil. Contrastingly, the emissions of greenhouse gases (GHG) such as carbon dioxide (CO 2 ) and nitrous oxide (N 2 O) occurring during dung decomposition are ecological disservices. The decomposition rates of dung and the rates of GHG produced during dung decomposition can vary depending on dung and soil characteristics. This study investigated the soil and dung properties and the bacterial communities that contribute to the decomposition rates of dung and their emission patterns under different farms in Hokkaido, Japan. We incubated dung and soil samples from 15 different grazed dairy farms. Soil and dung DNA were extracted at 0, 100, and 200 days during incubation and sequenced targeting changes in bacterial communities. Soil and dung physicochemical properties were measured before incubation. Changes in CO 2 and N 2 O emission rates were also monitored for 200 days. The results showed a positive correlation between soil carbon (C), nitrogen (N), and cation exchange capacity (CEC) to CO 2 emissions. Bacterial community analysis indicated that the increase in the amount of Proteobacteria , Acidobacteria , and Firmicutes in dung-treated soils contributed to the decrease in dung decomposition rates. This study clearly identified the effects of soil properties and the impact of the dung microbiome in regulating the decomposition rates of dung. Thus, these factors should be considered during dung decomposition and GHG in grazed dairy farms, especially within Hokkaido, Japan.