Concept:Denitrification is a process that removes nitrogen from the soil, not one that adds it.
Explanation:Soil nitrogen is gained through nitrogen fixation and the addition of organic matter.
Application of organic manure adds nitrogen-containing compounds to the soil.
Electrical discharge converts atmospheric nitrogen into nitrates that reach the soil.
Symbiotic nitrogen fixation by bacteria like Rhizobium adds nitrogen to the soil.
Denitrification, however, converts soil nitrates into gaseous nitrogen, which escapes into the atmosphere, causing nitrogen loss from the soil.
Therefore, denitrification is not a way the soil gains nitrogen.
Answer:A. Denitrification