How did nitrogen fertilizers increase agricultural production?

Nitrogen is a critical limiting factor for plant growth because, although it makes up about 78–79 percent of the atmosphere, plants cannot utilize it in its gaseous form (N₂). To be assimilated, nitrogen must first be "fixed" into reactive, water-soluble compounds such as ammonia or nitrates.123

Nitrogen fertilizers increased agricultural production by supplementing the natural supply of these compounds in the soil, which is often depleted in intensive agriculture where crops are harvested regularly without natural replenishment. The development of the Haber-Bosch process in the early 20th century was a turning point, as it allowed for the large-scale, economical synthesis of ammonia from atmospheric nitrogen and hydrogen.142

By providing plants with a reliable, concentrated source of essential nitrogen, these synthetic fertilizers enabled significantly higher crop yields. This technology became a cornerstone of modern scientific agriculture, supporting the increased productivity seen during the Green Revolution and helping to meet the global demand for food.562