NPK fertilisers are a type of compound chemical fertiliser that provides the three primary macronutrients essential for plant growth: Nitrogen (N), Phosphorus (P), and Potassium (K). The specific composition is indicated by a ratio of three numbers on the packaging, such as 10-26-26, which represents the percentage by weight of each nutrient.
The concept of mineral nutrition, which established that plants feed on minerals rather than just humus, was popularized by the German chemist Justus von Liebig around 1850, recognizing the relevance of N, P, and K. The industrial-scale production of the nitrogen component was later revolutionized by the Haber-Bosch process, discovered by Fritz Haber in 1909, which allowed for the synthesis of ammonia from atmospheric nitrogen. This innovation solved the problem of soil nutrient depletion, enabling a massive increase in agricultural productivity, which was foundational to the Green Revolution.
The mechanism of action is specific to each element: Nitrogen (N) is crucial for lush leaf and stem growth and chlorophyll formation; Phosphorus (P) supports strong root development, flowering, and fruiting; and Potassium (K) enhances overall plant health, water regulation, and disease resistance.
In India, NPK fertilisers are closely connected to the government's subsidy regime and agricultural policy. Non-urea NPK fertilisers are covered under the Nutrient-Based Subsidy (NBS) Scheme, which was launched in April 2010 and provides a fixed subsidy based on the nutrient content. This scheme aims to promote balanced fertilization, as India's national N:P:K consumption ratio remains skewed towards nitrogen, averaging around 9.8:3.7:1 compared to the recommended 4:2:1. Recently, the NBS framework has been revised to incorporate additional grades like 10:26:26 and 12:32:16 to encourage a more balanced nutrient application. Furthermore, the One Nation One Fertilizer scheme was introduced to mandate the use of the single brand name 'Bharat' for all subsidized fertilisers, including NPK, to ensure uniformity and transparency. The PM-PRANAM scheme, a recent initiative, also connects to NPK by incentivizing states to reduce the consumption of chemical fertilisers like NPK and promote alternatives.