I believe decaying plant matter generally emits green house gasses. (See for example emissions from biomass collecting behind dams; there were headlines about t

I believe decaying plant matter generally emits green house gasses. (See for example emissions from biomass collecting behind dams; there were headlines about this in the past year.) So you'd have to bury the biomass to prevent rot and/or gas leaks. That means digging big holes and/or transporting biomass to the holes and/or fabricating/moving material to cover the biomass. All that work uses energy and thus produces GHG. It's probably hard to come out ahead.