The soil organic carbon story

A good introduction to agricultural soil carbon -- what it is, what it does, how it forms -- from Saskatchewan, Canada.

"When soil was first broken by Europeans for crop production, SOC [soil organic carbon] decreased rapidly. There were several factors that accounted for this initial reduction: tillage broke up the soil and exposed much more soil organic matter to microbial decomposition, fallow periods promoted microbial breakdown of SOC by leaving soil moist without any new plant material additions, erosion of topsoil removed soil organic matter, and annual crops typically produced less residue than perennial crops (remember the roots!). When SOC was decreasing in the years after conversion to arable agriculture, great quantities of CO2 were released into the atmosphere that added to that released by burring fossil fuels. Generally, soil scientists believe much of the cropland in North America is now in approximate equilibrium under conventional management practices (ignoring losses of SOC in eroded sediment)."