Researchers at the University of Melbourne are holding a conference to discuss the importance of greenhouse gas emissions from soils.
A major concern is nitrous oxide from fertilizer, manure and biomass applications.
"300 times more potent than CO2, so even small emissions of this non-CO2 gas can make a considerable contribution to global warming” says Dr Stefan Arndt.
“When nitrogen is added to a wheat field as fertilizer or added to a pasture through animal faeces or clover swards, a part of the nitrogen can be lost as nitrous oxide, and when the weather conditions are right this can lead to large emissions of nitrous oxide” says Dr Eckard.
...not widely known [is] that soils can actually [take] methane out of the atmosphere. “Forest soils are especially efficient at taking up methane” says Dr Livesley.
At the present time there is not much knowledge about the magnitude of these non-CO2 emissions...
(revised May 18, 2007:)It is interesting that non-CO2 GHGs, like nitrous dioxide (NO2), aren't more in the news, considering their potential impact and (for NO2) a fascinating pattern of anthropogenicity.
Image source: Greenhouse gases, by Anyday.se
edit: revised intro to N02 map - yet again as my level of understanding evolves