Soil organic matter is made up of four major pools or fractions – plant residues, particulate organic carbon, humus carbon, and recalcitrant organic carbon. Plant residues and particulate fractions are also called labile soil OC. These pools vary in their chemical composition, stage of decomposition, and role in soil functioning and health. Each of the different carbon pools decomposes, or turns over, at a different rate.
Assume we have added organic amendments such as compost and manure to the soil. So, do the organic amendments decompose within a year to form the different pools or fractions of soil OC such as labile pool, humus, and recalcitrant pools?
@ Birhanu, I doubt, because only about 5 percent of added organic matter mineralizes yearly. That rate increases if temperature, oxygen, and moisture conditions become favorable for decomposition, which often occurs with excessive tillage. Moreover, the four major pools of soil organic matter i.e. plant residues, particulate organic carbon, humus carbon and recalcitrant organic carbon vary in their chemical composition, stage of decomposition and role in soil functioning and health.
Thank you Dr. Tarafdar. That means we may not find humus carbon and recalcitrant organic carbon 1 year after the addition of residues.
Can we increase the decomposition process by supplying temperature under controlled conditions?
What about the addition of charcoal?
Yes, definitely with increase in temperature up to 38 degree Celsius enhances organic matter decomposition. Organic matter decomposes slowly at lower temperatures as a result of decrease in microbial activities and biochemical processes. In general at favorable moisture conditions, increasing temperature results in an exponential increase in decomposition rates.
Unlike, other organic fertilizers, charcoal is very stable and it will not decompose to carbon dioxide. So once applied, it will stay in soil for hundreds to thousands of years. Therefore, you may get little effect of addition of charcoal on decomposition of organic matter.
Ok. This means whether compost, manure, or charcoal, by increasing temperature and accelerating their decomposition within a year, we can find the four fractions of soil organic carbon.
Birhanu, as I mentioned little effect of charcoal addition on decomposition but for compost and manure you may get all fraction provided you have optimum moisture and temperature in your system.
It is doubtful that all the added organic amendments decompose within a year to form various pools or fractions of soil OC (labile pool, humus, and recalcitrant pools). However, it depends upon the nature of the organic materials added and prevailing climatic condition etc.
Dr Jothimani you are right. That means the formation of resistant carbon pools increases with time.
The resistant organic pools may increase with time as stated by Dr. Birhanu Iticha. However, the quantity remain in lands also depends upon the soil and climatic conditions.
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