How Can I Measure Land-Applied Sludge Emissions?

Treatment and disposal of sewage sludge greatly contributes to greenhouse gas (GHG) emissions.   How are the GHG emissions from land application of municipal sludge usually estimated? How can I establish the correlation between methane and nitrous oxide emissions and dispersed biomass? Which tools are used for these measurements? I am trying to set up a simple tool for these measurements. Does anyone have advice on how to best achieve this?