Does overwintering change the inoculum effect on methane emissions from stored liquid manure?

Area of Science:

• Agricultural Science
• Environmental Science
• Microbiology

Background:

• Greenhouse gas (GHG) emissions, particularly methane (CH4), from dairy manure storage are significant.
• Methane production in manure relies on specific microbial communities (inoculum).
• Previous studies show spring manure removal effectively reduces CH4 emissions by eliminating inoculum.

Purpose of the Study:

• To investigate if fall removal of liquid dairy manure and its inoculum reduces CH4 emissions.
• To compare the effectiveness of fall versus spring inoculum removal for CH4 mitigation.
• To quantify emissions of CH4, N2O, NH3, and CO2 from manure storage under different inoculum conditions.

Main Methods:

• Six 11.88-m3 manure storage tanks were used, with three as inoculated controls (20% inoculum) and three as uninoculated treatments (0% inoculum).
• Inoculum was completely removed from treatment tanks in the fall/winter.
• Emissions of CH4, N2O, NH3, and CO2 were measured using flow-through chambers.

Main Results:

• Fall inoculum removal decreased total GHG emissions by 34% (CO2 equivalent) and the CH4 conversion factor by 29% compared to controls.
• Nitrous oxide (N2O) and ammonia (NH3) were minor contributors to the overall GHG budget (<2% CO2 equivalent).
• Fall removal was less effective in reducing CH4 emissions than spring removal reported in prior research.

Conclusions:

• Removing manure inoculum in the fall can reduce CH4 emissions from storage, but less effectively than spring removal.
• The timing of inoculum removal is a critical factor in the success of this CH4 mitigation strategy.
• Practical challenges exist for implementing complete, time-sensitive inoculum removal in large-scale farm manure storage systems.