Human activities such the production and application of fertilizer are part of the?

The air that is inhaled is about 20-percent oxygen, and the air that is exhaled is about 15-percent oxygen, so about 5-percent of the volume of air is consumed in each breath and converted to carbon dioxide. Therefore, a human being uses about 550 liters of pure oxygen (19 cubic feet) per day. The carbon dioxide The amount of inhaled air contains 21% oxygen and 0.04% carbon dioxide, while the air we breathe out contains 16.4%  oxygen and 4.4% carbon dioxide. This is because our cells use oxygen from the inhaled air to release energy and give out carbon dioxide as a byproduct. After a human breathes in Earth's air (roughly 78 percent nitrogen and 21 percent oxygen), he or she exhales a mixture of compounds similar to the air inhaled: 78 percent nitrogen, 16 percent oxygen, 0.09 percent argon, and four percent carbon dioxide.

I hope this helps :) if not then imma give you this in return <(^w^<)