Removing plants from an area, as we do when we harvest crops, removes a great deal of nitrogen. One of the ways farmers enable soils to naturally recover nitrogen content is:

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Planting the field with legumes is the best choice as legumes have a symbiotic relationship with nitrogen-fixing bacteria that can convert atmospheric nitrogen into organic nitrogen that can be used by plants, thus increasing the nitrogen content of the soil naturally. Adding industrially produced fertilizer (A) may enhance the nitrogen content of the soil, but it is not a natural process and can lead to environmental problems. Adding bacteria to the soil (C) can increase the nitrogen content of soil, but it is not always effective and may depend on soil conditions. Leaving the soil bare (D) can actually lead to nitrogen depletion as nitrogen-fixing plants are not present.

Removing Plants from an Area, as We Do When We