Fertilizer
A fertiliser is any natural or synthetic material applied to soil or plant tissues to supply nutrients essential for plant growth. Fertilisers differ from liming agents and other soil amendments that alter soil structure or pH without adding plant nutrients. Modern agriculture relies heavily on the use of fertilisers to maintain soil fertility and achieve high crop yields, with applications ranging from industrial-scale mechanised spreading to small-scale hand application. Fertilisers may be organic—derived from natural materials such as manure, compost, and mineral deposits—or inorganic, produced through industrial chemical processes.
Historical Development of Fertiliser Use
Management of soil fertility has been central to agriculture since its earliest origins. Civilisations in the Middle East, China, Mesoamerica, and the Central Andes used minerals, manure, crop rotation, and household waste to replenish soils and support population growth. Classical societies such as the Egyptians, Romans, Babylonians, and early Germans also recorded the use of manures and mineral additives to enhance agricultural productivity.
Systematic scientific research into plant nutrition evolved during the eighteenth and nineteenth centuries. Although Justus von Liebig is often credited with foundational work in plant nutrition, earlier figures such as Nicolas-Théodore de Saussure, along with contemporaries Carl Ludwig Sprenger and Hermann Hellriegel, contributed significantly to the discipline. In Britain, John Bennet Lawes pioneered artificial fertiliser production by patenting a phosphate-based manure in 1842, later collaborating with Joseph Henry Gilbert in landmark long-term crop experiments at Rothamsted.
The industrial era saw further breakthroughs. The Birkeland–Eyde process, developed in Norway at the start of the twentieth century, used electric arcs to convert atmospheric nitrogen into nitric acid. Shortly thereafter, the Haber–Bosch process revolutionised nitrogen fertiliser production by synthesising ammonia from atmospheric nitrogen and hydrogen derived from natural gas. The Ostwald process, developed in parallel, enabled the efficient conversion of ammonia into nitric acid. These innovations dramatically increased the availability of nitrogen fertilisers and are widely regarded as enabling the global population expansion of the twentieth century.
Following the Second World War, industrial plants originally used for wartime explosives were repurposed for fertiliser production, contributing to a dramatic rise in global use. Between 1961 and 2019, nitrogen fertiliser consumption increased eightfold, underpinning the Green Revolution and supporting rapid increases in crop yields.
Global Production and Use
Inorganic fertiliser use in 2021 totalled approximately 195 million tonnes of nutrients, of which nitrogen accounted for more than half. Asia is the largest consumer, followed by the Americas, Europe, Africa, and Oceania. China, India, Brazil, and the United States are the leading national users. Specific crop requirements vary: for example, maize yielding 6–9 tonnes per hectare may require substantial phosphate inputs, whereas soybeans typically require about half that amount.
Yara International is among the largest global producers of nitrogen-based fertilisers.
Types of Fertilisers and Their Functions
Fertilisers supply nutrients in proportions that support plant growth and maintain soil productivity. They typically provide:
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Primary macronutrients
- Nitrogen (N): essential for leaf and stem growth; found in amino acids, nucleic acids, and chlorophyll.
- Phosphorus (P): vital for root development, flowering, seed production, ATP energy cycles, and nucleic acids.
- Potassium (K): strengthens stems, aids water regulation, and promotes flowering and fruiting.
- Secondary macronutrients
- Micronutrients
Plants also rely on hydrogen, oxygen, and carbon, readily available from water and atmospheric carbon dioxide. Although nitrogen is abundant in the atmosphere, it is not directly usable by plants. Only certain bacteria and symbiotic plant species such as legumes can fix atmospheric nitrogen into ammonia.
Mechanisms of Fertiliser Action
Fertilisers promote plant growth through two main mechanisms:
- Providing essential nutrients – especially N, P, and K, which plants absorb through their root systems.
- Improving soil properties – some fertilisers enhance soil water retention, aeration, or structure.
Nitrogen fertilisers are particularly significant due to nitrogen’s role in proteins, nucleic acids, and metabolic compounds. Phosphorus is required for energy transfer molecules such as ATP, as well as for DNA and membrane phospholipids.
Biological and Microbiological Considerations
Effective fertiliser use depends on complex soil–microbe interactions. Two key microbial processes influence nitrogen fertiliser efficiency:
- Urease activity – many soil bacteria possess urease, an enzyme that catalyses the hydrolysis of urea into ammonium and bicarbonate. This reaction influences nutrient availability and soil pH.
- Nitrification – ammonia-oxidising bacteria such as Nitrosomonas convert ammonia to nitrite, which is then oxidised to nitrate by Nitrobacter. Nitrate is highly soluble and can leach into waterways, contributing to eutrophication.
Understanding these microbial pathways is essential for reducing nutrient losses and environmental impacts.
Environmental Impacts and Sustainability
While synthetic fertilisers have been crucial for boosting global food production, their widespread use has environmental consequences. These include:
- Water pollution and eutrophication, caused by nutrient runoff into rivers, lakes, and coastal systems.
- Greenhouse gas emissions, particularly from nitrogen fertiliser production and soil microbial processes.
- Soil contamination from excessive or imbalanced fertiliser use.
- Resource depletion, especially concerning phosphorus reserves.
Sustainable agricultural practices aim to minimise negative impacts through methods such as precision fertiliser application, integrated nutrient management, organic amendments, cover cropping, and reduced reliance on synthetic inputs.
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