2022 Volume 93 Issue 3 Pages 97-107
Composting tests based on nonaerated static pile composting were conducted on a realistic scale following the agricultural habits used in Hokkaido to examine the effects on greenhouse gas emissions of controlling dairy manure moisture content by mixing the manure with wheat straw. Test plots included three different moisture contents with specific gravity levels: high, 82.3% with 888 kg m−3; medium, 79.1% with 796 kg m−3; and low, 75.9% with 679 kg m−3. Greenhouse gas emissions and the temperature of the compost were measured throughout the composting process (111 days). The highest temperatures were 44.7°C, 71.9°C, and 71.1°C in high, medium, and low moisture content compost, but compost temperatures were in the following order during the entire composting period: low>medium>high moisture content. The degrees of compost maturity were nearly immature and fully mature with high and low moisture content, respectively, and the degree was intermediate between the two maturities with medium moisture content. Thus, composting proceeded in a swollen/softened state and an aerobic state with low moisture content, whereas the anaerobic state was mostly found when moisture content was high. Cumulative emission rates of methane and nitrous oxide gases were in the following order: low<high<medium moisture content. This indicated that greenhouse gas emissions could be controlled by mixing a large amount of wheat straw into the compost. Cumulative greenhouse gas emissions converted to CO2 equivalents were 572, 850, and 518 kg-CO2eq with high, medium, and low moisture content, respectively. Thus, with low moisture content, emissions were reduced by 9.4% and 39.1% compared with those when moisture content was high and medium, respectively. These results indicate that composting by actively mixing wheat straw into dairy manure to adjust moisture content can lead to swollen and softened compost and accelerated fermentation, which could help reduce greenhouse gas emissions from dairy farms.
