What are Chemical Fertilizers?

Chea Takihiro ​​ភាសារខ្មែរ l English

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1. What is Fertilizer?

Fertilizer is an indispensable food for plants. All living organisms on Earth cannot survive without food, and similarly, plants cannot grow and thrive without nutrients.

In 1828, German agricultural scientist Carl Sprengel formulated a theory stating that plant growth is dictated by the essential nutrient present in the most limiting quantity. This concept became known as the “Law of the Minimum”.

This theory is illustrated using the wooden barrel analogy: a barrel can hold water up to its full capacity only if all its wooden staves are of equal height and properly sealed. However, if even a single stave is shorter than the rest, the water will spill out at the height of that shortest stave. In agricultural terms, no matter how abundant other nutrients are in the soil, if a single essential element is deficient, the plant cannot achieve full growth.

Later in 1840, German chemist Justus von Liebig further popularized and expanded upon this theory, leading to widespread global recognition. Through extensive research and experimentation, he demonstrated that the three primary essential nutrients for plants are Nitrogen (N), Phosphorus (P), and Potassium (K).

2. Essential NPK Nutrients for Plants

Primary NPK nutrients represent the three macronutrients essential for plant life. Before the Green Revolution, farmers identified soil fertility needs primarily through visual observation:

• Nitrogen (N): Promotes the growth of stems and leaves. Grasses and green vegetation contain high concentrations of nitrogen. Grass serves as the primary food source for herbivores (cattle, goats, sheep, horses), which in turn serve as main food sources for carnivores and humans. Animal manure was historically collected and used as fertilizer for leafy vegetables and crops in their vegetative growth stage.
• Phosphorus (P): Crucial for root development, flowering, fruiting, and seed production. Crops with high fruit and seed yields—such as rice, wheat, corn, coffee, and fruit trees—require substantial phosphorus. These crops form the cornerstone of human food security and animal feed production.
• Potassium (K): Strengthens plant immunity, enhancing resistance against diseases, water stress, and harsh weather conditions. Traditional methods of obtaining potassium relied on wood ash and decaying organic matter.

The Interconnected Ecosystem: Decaying wood and organic matter harbor hundreds of millions of beneficial microorganisms. Through compost decomposition, these microorganisms break down N, P, and K into plant-absorbable forms while actively suppressing soil-borne pathogens. This creates a balanced, sustainable natural ecosystem.

3. The Green Revolution and the Haber-Bosch Process

Global conflicts and world wars forced humanity to innovate rapid food production systems, as traditional farming could not keep pace with exploding population growth and widespread famine.

• The Haber-Bosch Process: In 1909, chemist Fritz Haber discovered a method to fix atmospheric nitrogen gas (N₂) into ammonia (NH₄⁺). In 1913, Carl Bosch scaled this breakthrough into an industrial process, now known as the Haber-Bosch Process.

• Mechanism of Action: Synthetic chemical fertilizers are produced as inorganic salts that dissolve rapidly in water. Upon soil application and hydration, they instantly dissociate into free ions such as Nitrate (NO₃⁻), Ammonium (NH₄⁺), Phosphate (HPO₄²⁻), and Potassium (K⁺). Plant roots absorb these inorganic ions directly without waiting for microbial decomposition (mineralization), resulting in rapid vegetative growth, dark green foliage, and visible changes within days.

4. Negative Impacts of Chemical Fertilizer Overuse

• Soil Health: Prolonged and excessive use of synthetic nitrogen fertilizers causes soil acidification, soil compaction, loss of aeration, salinization, and the destruction of beneficial soil bacteria, fungi, and soil organic matter.
• Crop Quality: Over-application of nitrogen causes rapid, structurally weak vegetative growth, making plants prone to lodging, reducing natural pest/disease resistance, and shortening post-harvest shelf life while diminishing flavor.
• Human Health:
  • Nitrate (NO₃⁻) Leaching: Excess nitrates leach into groundwater. Drinking nitrate-contaminated water causes oxygen deprivation in infants (Methemoglobinemia or Blue Baby Syndrome). In the human digestive system, nitrates convert into N‑nitroso compounds, increasing cancer risks.
  • Heavy Metals: Certain phosphate fertilizers contain Cadmium (Cadmium), a heavy metal that bioaccumulates in crops, causing renal damage and bone degradation upon human consumption.

Safe Usage Limits for Chemical Fertilizers

There is no universal standard defining an “absolutely safe” quantity of synthetic fertilizer for soil, as requirements vary depending on crop type, soil condition, and whether additional synthetic agrochemicals (such as herbicides or pesticides) are applied.

However, as a foundational principle, if farmers use chemical fertilizers alone without applying additional synthetic chemicals:

Crop Category	Safe Annual Synthetic Fertilizer Limit	Mandatory Condition (Organic Compost Supplement)
Large Fruit Trees (Coffee, Avocado, Durian)	Under 1 kg per tree	Add 10 – 15 kg of compost per tree
Field/Row Crops (Rice, Beans)	Under 20 – 50 g/m² (200 – 300 kg/ha)	Add 10 – 15 kg of compost per m²

Important Note: If farmers apply chemical fertilizers—even in minimal quantities below 500 grams—without returning organic compost or organic matter back to the soil, the soil will still suffer severe long-term degradation and nutrient depletion due to the disruptive presence of synthetic chemicals.

5. Reports from Major International Organizations (FAO, UNEP, WHO)

1. Food and Agriculture Organization (FAO, 2015): Soil Degradation The Status of the World’s Soil Resources report highlights that excessive application of synthetic nitrogen fertilizers accelerates soil acidification and mineral imbalances.

• Impact on Nature: Destroys soil organic matter and kills beneficial microorganisms, leaving approximately 33% of global agricultural soils degraded.
• Impact on Animals: Decimates soil fauna (e.g., earthworms). Livestock grazing on nutrient-deficient land suffer from micronutrient deficiencies.
• Impact on Humans: Increases farmer dependency on costly chemical inputs, reduces long-term yield potential, and threatens global food security.

2. United Nations Environment Program (UNEP, 2019): Eutrophication and Aquatic “Dead Zones” The Global Environment Outlook (GEO-6) report documents how unabsorbed nitrogen (N) and phosphorus (P) runoff enters aquatic ecosystems, driving severe eutrophication.

• Impact on Nature: Triggers massive toxic algal blooms (Cyanobacteria). As algae die, bacterial decomposition consumes dissolved oxygen, creating over 400 oceanic and freshwater “Dead Zones” (hypoxic zones) globally.
• Impact on Animals: Causes mass die-offs of fish, crustaceans, and marine life, while cyanotoxins poison waterfowl and terrestrial animals drinking contaminated water.
• Impact on Humans: Devastates commercial fisheries and aquaculture, destroys wild protein sources, and poses severe toxicity risks through contaminated seafood and drinking water.

3. World Health Organization (WHO, 2011): Groundwater Contamination and Health Risks WHO guidelines show that excess nitrate (NO₃⁻) readily leaches into groundwater aquifers used for drinking water.

• Impact on Nature: Causes long-term groundwater pollution requiring decades or centuries to naturally recover.
• Impact on Animals: Livestock consuming high-nitrate well water suffer chronic toxicity, reduced milk production, spontaneous abortion, and acute mortality.
• Impact on Humans:
  • Infants: Causes Methemoglobinemia (Blue Baby Syndrome), where nitrites bind hemoglobin, blocking oxygen transport and proving fatal without immediate intervention.
  • Pregnant Women: Increases risks of miscarriage and fetal neurodevelopmental impairment.
  • Adults: Ingested nitrates form carcinogenic N‑nitroso compounds in the stomach, significantly increasing the incidence of gastric and colorectal cancers.

We cannot completely stop using fertilizers and chemicals in the short or medium term. However, excessive use of chemical fertilizers poses a serious risk to future generations, leaving them with infertile soil. Reducing chemical fertilizer use and adding compost is a practical solution we can achieve together.

I would like to express my respect to all farmers who are currently practicing agriculture under unpredictable natural conditions. Yet, we must also ensure that we do not leave behind multiple problems for the generations to come.

References

Food and Agriculture Organization of the United Nations (FAO), and Intergovernmental Technical Panel on Soils (ITPS). 2015. Status of the World’s Soil Resources (SWSR) – Main Report. Rome: FAO.

Liebig, Justus von. 1840. Organic Chemistry in Its Applications to Agriculture and Physiology. Edited by Lyon Playfair. London: Taylor and Walton.

Sprengel, Carl. 1828. “Von dem Relativem Werthe der Verschiedenen Düngmittel.” Journal für Technische und Ökonomische Chemie 3: 42–49.

United Nations Environment Programme (UNEP). 2019. Global Environment Outlook – GEO-6: Healthy Planet, Healthy People. Cambridge: Cambridge University Press.

World Health Organization (WHO). 2011. Guidelines for Drinking-water Quality. 4th ed. Geneva: World Health Organization.