The soil gains nitrogen through one of the following except?

The soil does not gain nitrogen through electrical discharge. Electrical discharge, such as lightning, can cause nitrogen to react with oxygen in the air to form nitrogen oxides, which can then dissolve in rain and enter the soil. However, this process is not a significant source of nitrogen for the soil. The three other options listed can all contribute to the soil gaining nitrogen. Denitrification is the process by which bacteria convert nitrates in the soil back into atmospheric nitrogen, which can then be used by other plants. Application of organic manure, such as compost or animal manure, adds organic matter to the soil that contains nitrogen, which can then be broken down by bacteria and released as a nutrient for plants. Symbiotic nitrogen fixation is a process where certain plants, such as legumes, have a mutually beneficial relationship with nitrogen-fixing bacteria in their root nodules, which allows the plants to use atmospheric nitrogen for their own growth. In summary, while electrical discharge can cause nitrogen to enter the soil in the form of nitrogen oxides, it is not a significant source of nitrogen for the soil, whereas denitrification, application of organic manure, and symbiotic nitrogen fixation are all ways in which the soil can gain nitrogen.