Estimation of net greenhouse gas emission from a paddy field

I know that irrigation is the biggest contributor in green house gas emission in agriculture. I work in paddy research centre and want to know how to calculate or estimate net green house gas emission from the paddy feild. We mostly grow rice in bunded fields and maintain 5-10 cm of water level in each bund. I want to know this as we wish to reduce the GHG emmision from the feild by adopting different and better irrigation method over this old flood irrigation system.