Answer: D-by decomposing it.
The organic matter present in the soil is decomposed by enzymatic biochemical reactions through the bacteria, microbes and worms present in the soil. The soil organic matter constitutes mostly animal and plant residues.
Majority of the organic matter is broken down by microbes or bacteria through enzymatic biochemical chemical reactions into CO2, water and heat.
The nitrogen, phosphorus and sulphur are mineralised and liberated into the air by several reactions.
Compounds which are resistant to the microbial reactions are modified into various componds or synthesized into new compounds by the microbes to form humus.
