Why mineral fertilizers are essential for food security

Concerns about environmental damage caused by mineral fertilizer use – and even a presumed adverse impact on food security – have prompted negative responses and rejection of mineral fertilizer use from society and some scientists who claim that the world can be fed completely through the use of organic fertilizers.

These views tend to reject basic eco-physiological processes and even basic physical, mineral and biological laws. They may generate false hope and stimulate counterproductive measures and pleas for extreme options to resolve the global pressure on natural resources and human suffering. While the intentions may be honorable, the means could be erroneous. Ecologically durable options can be arrived at only when basic processes and laws are respected.

Without mineral fertilizers, the conversion of inert nutrients to reactive nutrients for biological processes should be obtained from physical processes like lighting converting N2 into reactive nitrogen; physical-chemical processes like weathering of parent material forming soils; and from biological processes, primarily fixation by bacteria living in symbiosis with legumes. Based on nitrogen balance analyses, such “natural” fertilizers support a maximum yield per hectare of 2-2.5 metric tons (mt) of grain equivalents (GE). This is true only when legumes are grown under otherwise optimal conditions, i.e., with sufficient water and fertile soils that provide all other nutrients, primarily phosphorus. These yield levels are comparable to yields in Europe and North America in the year 1900, prior to the use of mineral fertilizers. Nutrients would be accumulated on the crop field from manure of grazing cattle in the surroundings and waste from the cities. Hence, natural processes have limits.

Often, organic yields are compared with conventional yield levels and found to be higher. At low conventional yield levels of less than 2 mt per hectare, better care of crops with closed nutrient cycles can indeed be higher than conventional cultivation with less attention to these practices. Organic yields of 6 mt per hectare, as found for instance in the Netherlands, have been shown to result from nutrients imported from other fields and internationally traded feed.

A vegetarian diet requires 1.5 kilograms (kg) of GE per person per day. If all were to become vegetarians, 5 billion mt of GE would be needed for the world’s 9 billion people in 2050. At 2 mt per hectare, agriculture would have to expand to 2.5 billion hectares (1 billion hectares more than the current 1.5 billion), with dramatic implications for biodiversity. If all were to adopt a European dietary level of 4.5 kg of GE, a total of over 7 billion hectares would be needed, which exceeds all the available land on Earth. Hence, the “artificial” conversion of N2 into reactive nitrogen is essential if everyone is to be fed. Human interventions to convert other inert nutrients as found in ore into reactive nutrients (like phosphorus, potassium, zinc, iron and copper) are equally important for attaining yields exceeding natural yield levels.

Both overuse and underuse of mineral fertilizers should be prevented. However, we cannot allow emotions to cloud our understanding of fundamental natural laws. To feed a world population without mineral fertilizers would irreparably damage biodiversity and would cause human suffering.