By what process is carbon released into the atmosphere from soil...

...that is being farmed on using industrial agricultural methods? I am just curious. Say you've got a field of mono cropped corn sprayed with fertilizers and biocides. The plants take in carbon in the process of photosynthesis, that carbon turns into the plant, plant is removed from site after harvest so no carbon makes it into the soil in the form of organic matter, but how is carbon leaving the soil and going into the atmosphere? Maybe the plowing is what does it??? If plowing is the main cause can someone explain what's going on at the microscopic level of what's happening when you plow? Bacteria eating OM and farting out carbon or what??

As I understand it, it's because of the plowing which speeds up the breakdown of organic matter in the soil so carbon that was in stable forms like humus gets released again as CO2.

This article has a lot of information which might help - soil carbon storage

This one is good too - soil health - organic matter

Here's a quote

Large losses of soil organic matter can be attributed to cultivation. Organic matter that is inside aggregates or coated with soil particles is protected by decomposition because microorganisms are unable to come into physical contact with it. Tillage disturbs the soil and brings "protected" organic matter in to physical contact with microorganisms, which then decompose it. No-till systems can overcome this problem. No-till systems also decrease soil erosion. Organic matter and microorganisms are restricted to the top layers of the soil. This increases the potential for losing organic matter if management practices cause soil loss.

Do you know where I can read more in depth about this?

Oh nvm Thanks! Just saw your suggestions for further details.

Its no different than the process by which carbon breaks down in your compost pile, much of that carbon gases-off, while a smaller percentage of bio-mass is left that remains somewhat stable.

Soil carbon, when exposed to a significant bump in oxygen, decomposes via microbial activity eating that carbon.  When you turn your compost pile, the microbes "bloom" and rapidly multiply, eating available food sources.  When you turn your soil, the exact same thing happens.

nick bramlett wrote:... Bacteria eating OM and farting out carbon or what??

Pretty much, but add to it some inorganic processes possibly and also other organisms that take in oxygen and expel CO2 in addition to bacteria.

Don't forget about nitrogen fertilizers.  Tilling plus some nitrogen fertilizer really speeds the break down of topsoil.  

The natural cycle is one of balance in a no till situation. There is a mix of aerobic and anaerobic life in the soil which break down sequestered carbon and release it's energy for reuse.  When we till the soil and add more oxygen into the mix, the carbon is released very quickly for a short period of time, but eventually the soil becomes depleted and reintroduction of nitrogen and even carbon for soil structure is necessary--this is a huge waste of energy and thus to be avoided.