Short answers, pulled from the story.
Fertilizer is any natural or synthetic material applied to soil or plant tissue to supply plant nutrients. Most modern fertilization focuses on three macronutrients: nitrogen (N) for leaf and stem growth, phosphorus (P) for roots, flowers, seeds, and fruit, and potassium (K) for strong stems and the movement of water in plants.
The N-P-K rating is three numbers, such as 16-4-8, describing the percentage of nitrogen, phosphorus expressed as P2O5, and potassium expressed as K2O. A 50 lb bag labeled 16-4-8 contains 8 lb of nitrogen, since nitrogen is 16% of the 50 pounds. Fertilizers do not actually contain P2O5 or K2O, so the system is a conventional shorthand.
German chemist Justus von Liebig is most often called the father of the fertilizer industry, though scientific research on plant nutrition started before his work. John Bennet Lawes patented a manure made by treating phosphates with sulfuric acid in 1842, becoming the first to create the artificial manure industry.
The Haber process produces ammonia from natural gas and atmospheric nitrogen, and that ammonia is the feedstock for nearly all nitrogen fertilizers. After World War II, nitrogen plants that had ramped up for wartime bomb manufacturing were pivoted toward agriculture, and nitrogen fertilizer use rose 800% between 1961 and 2019.
Excess fertilizer causes water pollution and eutrophication through nutrient runoff, with phosphate feeding algal blooms that consume oxygen and create ocean dead zones. Nitrogen fertilizer accounts for about 5% of human-caused greenhouse gas emissions, and nitrate levels above 10 mg/L in groundwater can cause blue baby syndrome.
China is the largest user of every fertilizer nutrient, followed by India, Brazil, and the United States. Asia represented 56% of the world's total agricultural use of inorganic fertilizers in 2023, ahead of the Americas at 27%, Europe at 11%, Africa at 4%, and Oceania at 2%.