Fertilizer

A fertilizer or fertiliser is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from liming materials or other non-nutrient soil amendments. Many sources of fertilizer exist, both natural and industrially produced. For most modern agricultural practices, fertilization focuses on three main macro nutrients: nitrogen (N), phosphorus (P), and potassium (K) with occasional addition of supplements like rock flour for micronutrients. Farmers apply these fertilizers in a variety of ways: through dry or pelletized or liquid application processes, using large agricultural equipment, or hand-tool methods.

Historically, fertilization came from natural or organic sources: compost, animal manure, human manure, harvested minerals, crop rotations, and byproducts of human-nature industries (e.g. fish processing waste, or bloodmeal from animal slaughter). However, starting in the 19th century, after innovations in plant nutrition, an agricultural industry developed around synthetically created agrochemical fertilizers. This transition was important in transforming the global food system, allowing for larger-scale industrial agriculture with large crop yields.

Nitrogen-fixing chemical processes, such as the Haber process invented at the beginning of the 20th century, and amplified by production capacity created during World War II, led to a boom in using nitrogen fertilizers. In the latter half of the 20th century, increased use of nitrogen fertilizers (800% increase between 1961 and 2019) has been a crucial component of the increased productivity of conventional food systems (more than 30% per capita) as part of the so-called "Green Revolution".

The use of artificial and industrially applied fertilizers has caused environmental consequences such as water pollution and eutrophication due to nutritional runoff; carbon and other emissions from fertilizer production and mining; and contamination and pollution of soil. Various sustainable agriculture practices can be implemented to reduce the adverse environmental effects of fertilizer and pesticide use and environmental damage caused by industrial agriculture.

Management of soil fertility has preoccupied farmers since the beginning of agriculture. Middle Eastern, Chinese, Mesoamerican, and Cultures of the Central Andes were all early adopters of agriculture. This is thought to have led to their cultures growing faster in population which allowed an exportation of culture to neighboring hunter-gatherer groups. Fertilizer use along with agriculture allowed some of these early societies a critical advantage over their neighbors, leading them to become dominant cultures in their respective regions (P Bellwood - 2023). Egyptians, Romans, Babylonians, and early Germans are all recorded as using minerals or manure to enhance the productivity of their farms. The scientific research of plant nutrition started well before the work of German chemist Justus von Liebig although his name is most mentioned as the "father of the fertilizer industry". Nicolas Théodore de Saussure and scientific colleagues at the time were quick to disprove the simplifications of von Liebig. Prominent scientists whom von Liebig drew were Carl Ludwig Sprenger and Hermann Hellriegel. In this field, a 'knowledge erosion' took place, partly driven by an intermingling of economics and research. John Bennet Lawes, an English entrepreneur, began experimenting on the effects of various manures on plants growing in pots in 1837, and a year or two later the experiments were extended to crops in the field. One immediate consequence was that in 1842 he patented a manure formed by treating phosphates with sulfuric acid, and thus was the first to create the artificial manure industry. In the succeeding year, he enlisted the services of Joseph Henry Gilbert; together they performed crop experiments at the Institute of Arable Crops Research.

The Birkeland–Eyde process was one of the competing industrial processes at the beginning of nitrogen-based fertilizer production. This process was used to fix atmospheric nitrogen (N₂) into nitric acid (HNO₃), one of several chemical processes called nitrogen fixation. The resultant nitric acid was then used as a source of nitrate (NO₃⁻). A factory based on the process was built in Rjukan and Notodden in Norway and large hydroelectric power facilities were built.

The 1910s and 1920s witnessed the rise of the Haber process and the Ostwald process. The Haber process produces ammonia (NH₃) from methane (CH₄) (natural gas) gas and molecular nitrogen (N₂) from the air. The ammonia from the Haber process is then partially converted into nitric acid (HNO₃) in the Ostwald process. It is estimated that a third of annual global food production uses ammonia from the Haber–Bosch process and that this supports nearly half the world's population. After World War II, nitrogen production plants that had ramped up for wartime bomb manufacturing were pivoted towards agricultural uses. The use of synthetic nitrogen fertilizers has increased steadily over the last 50 years, rising almost 20-fold to the current rate of 100 million tonnes of nitrogen per year.

The development of synthetic nitrogen fertilizers has significantly supported global population growth. It has been estimated that almost half the people on the Earth are currently fed due to synthetic nitrogen fertilizer use. The use of phosphate fertilizers has also increased from 9 million tonnes per year in 1960 to 40 million tonnes per year in 2000.