Temperatures of compost piles are insufficiently high to kill viruses. Weeds may be controlled by covering the pile with plastic to prevent the growth and maturation of any plants that start in the pile from the germination of weed seeds. As a safety precaution, diseased material should not be added to the pile. During composting half or more of the bulk of the pile is lost by decomposition, waste, or unavoidable losses. At least half of the carbon is lost.
Microorganisms use the organic material as a source of energy.
Respiratory loss of carbon dioxide represents most of the loss of carbon. Nitrogen is lost by volatilization of ammonia and leaching and denitrification of nitrate. N ratio is narrowed. Potassium is lost by leaching. Phosphorus is conserved, for it is mostly in insoluble compounds that are neither leached nor lost as gaseous substances.