Another Question re Soil Quality

I must say I am impressed with the recent dialogue/exchanges re soil 
quality and am learning a lot.  But to inspire you all to rise to the 
occassion of educating those of us trained in the less than relevant 
disciplines, I have a basic question.  Is the amount of carbon in the 
world fixed?  Do humans simple move it around by what they do with 
biomass and soils?  How is carbon different from nitrogen?

	I would welcome some general discussion of carbon, 
supply-uses-balances-fluxes, and how these are impacted by agricultural 
management practices.  

	I have been spending serious chunks of time in recent days 
writing re soil quality and its importance in protecting water quality 
and in assuring a sustainable, profitable, fulfilling future for American 
agriculture, and society as a whole.  I need to understand carbon better 
to take my discussions to the next level.