METHANE EMISSIONS FROM MANURE STORAGES

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 10 degrees C and 20 degrees C 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 10 degrees C and 20 degrees C. It produced twice as much methane at 20 degrees C as at 10 degrees C. Frequent removal in the summer would significantly reduce methane emissions from manure stored on farm B, since an average manure temperature of 22 degrees C 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 10 degrees C and 20 degrees C, respectively, over the 370-day monitoring period. Additionally, manure A produced methane after a lag phase of about 250 days at 20 degrees C, 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.