Methane Emissions from Manure Storages

Abstract

The objectives of this study were to measure methane emissions from liquid manure stored on two farms (farm A and farm B) in eastern Canada and to evaluate the effect of various mitigation strategies on methane emissions. Manure from the two farms was kept at 10C and 20C for a 370-day period in storage pilots. The temperature profile in the storage tanks of both farms was also monitored during the experimental period. Manure from farm B (manure B) emitted methane soon after it was loaded to the storage pilots at 10C and 20C. It produced twice as much methane at 20C as at 10C. Frequent removal in the summer would significantly reduce methane emissions from manure stored on farm B, since an average manure temperature of 22C was measured during the summer storage period. Manure from farm A (manure A) produced 3% and 54% of the methane emitted by manure B at 10C and 20C, respectively, over the 370-day monitoring period. Additionally, manure A produced methane after a lag phase of about 250 days at 20C, which, on most farms, is longer than the storage period between land applications. Methane production from manure stored on farm A should then be minimal. Results were used to simulate the impact of mitigation practices on methane production from the full-scale storage structures on both farms. Increasing manure removal from 2 to 3 times a year and leaving the cows outside during summer nights decreased methane emissions by averages of 9% and 12%, respectively. Reducing the depth of residual manure left in the tank after land application from 60 to 30 cm reduced methane emissions by an average of 26%. The manure remaining in the storage structure becomes an important source of adapted inoculum that can readily produce methane. In every scenario, manure A produced about 3% of the methane emitted by manure B per kg of milk produced. The important difference between the two farms shows the large error that would arise from estimating methane production using a single emission factor for all farms within a region.