Fertilizer (American English) or fertilizer (British English; see spelling differences) is any natural or synthetic material used for soil or tissue planting to provide plant nutrients. Fertilizers can vary from lime or other non-nutrient soils. There are many natural, organic and industrial fertilizers available. In many modern agricultural practices, fertilization focuses on three major macro elements: Nitrogen (N), Phosphorus (P), and Potassium (K) by the occasional addition of additives such as rock dust to micronutrients. Farmers use this fertilizer in a variety of ways: through dry or extracted systems with water or liquid, using large agricultural machinery or hand tools.

Historically fertilization came from natural or organic sources: manure, animal manure, human manure, harvested minerals, crop rotation and man-made industrial products (i.e. fish contamination, or bleeding from animal slaughter). However, from the 19th century, after the invention of plant foods, the agricultural industry developed man-made fertilizer. These changes have been instrumental in transforming the global food system, allowing for greater industrial agriculture with larger crop yields. In particular the chemical processes for nitrogen fixation such as the Haber process in the early 20th century, which increased production capacity during World War II led to the use of nitrogen fertilizers. In the next half of the 20th century, increased use of nitrogen fertilizers (an increase of 800% between 1961 and 2019) became an integral part of the growing production of conventional food systems (over 30% per person) as part of the so-called “I- Green Revolution “.