Seasonal Variation in Methane Emission from Stored Slurry and Solid Manures
- Søren Husted *
Methane (CH4) is an important greenhouse gas and recent inventories have suggested that livestock manure makes a significant contribution to global CH4 emissions. The emission of CH4 from stored pig slurry, cattle slurry, pig solid manure, and cattle solid manure was followed during a 1-yr period. Methane emission was determined by dynamic chambers. Emission rates followed a In-normal distribution for all four manures, indicating large spatial and seasonal variations. Monthly geometric means for pig slurry, cattle slurry, pig solid manure, and cattle solid manure varied from 0.4 to 35.8, 0.0 to 34.5, 0.4 to 142.1, and 0.1 to 42.7 g CH4 m−3 d−1, respectively. For slurries CH4 emission rates increased significantly with storage temperatures, the Q10 value ranging from 3.4 to 5.7 depending on slurry type. The presence of a natural surface crust reduced CH4 emission from slurry by a factor of 11 to 12. Surface crust effects declined with increasing slurry temperature. Solid manures stored in dungheaps showed significant heat production. Pig solid manure temperatures were maintained at 30 to 60 °C throughout most of the year, while cattle solid manure temperatures were close to ambient levels until late spring, when heat production was initiated. Methanogenesis in solid manure also increased with increasing temperatures. For pig solid manure, CH4 emission rates peaked at 35 to 45 °C. No distinct temperature optimum could be detected for cattle solid manure, however, temperatures rarely exceeded 45 °C. The Q10 values for dungheaps ranged from 2.7 to 10.3 depending on manure type and Q10 temperature interval. Annual CH4 emissions from pig slurry, cattle slurry, pig solid manure, and cattle solid manure were estimated at 8.9, 15.5, 27.3, and 5.3 kg animal−1 yr−1, respectively. The annual emission of CH4 from stored animal manure in Denmark is estimated at 28 000 Mg yr−1.
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