That's why, since the beginning of agriculture, people have been applying fertilizers. We'll talk about nitrogen fertilizers. This is Earth and Sky.
Plants get enough carbon, hydrogen and oxygen from air and water.
But nitrogen is another story. This combination is known to chemists as N2. But natural processes like this have been supplemented by human activities since the beginning of agriculture. Since ancient times, people have used manure, guano and other substances to replenish the nitrogen in soil. About a century ago, humans began to make fertilizer in factories.