Chemistry of the Environment - Fertilizers

Plant Nutrients: Plants require three essential elements for healthy growth: Nitrogen ($N$), Phosphorus ($P$), and Potassium ($K$). These are often provided in the form of 'NPK fertilizers'.

Nitrogen ($N$): Essential for making proteins and chlorophyll. A deficiency leads to stunted growth and yellow leaves (chlorosis).

Phosphorus ($P$): Necessary for root development and energy transfer (ATP). A deficiency results in poor root systems and purple-tinted leaves.

Potassium ($K$): Required for enzyme activation, regulation of water movement (stomata), and the production of flowers and fruits.

Ammonium Salts: Most nitrogenous fertilizers are ammonium salts made by the neutralization of ammonia ($NH_3$). For example, reacting $NH_3$ with nitric acid ($HNO_3$) produces ammonium nitrate ($NH_4NO_3$).

Displacement of Ammonia: If an alkali such as calcium hydroxide ($Ca(OH)_2$) is added to soil containing ammonium fertilizers, a reaction occurs that releases ammonia gas ($NH_3$). This reduces the nitrogen content available to plants.

Eutrophication: The environmental process where excess fertilizers (nitrates and phosphates) leach into water bodies, causing rapid algae growth (algal blooms). This blocks sunlight, leading to the death of plants below, bacterial decomposition of dead matter, and the depletion of dissolved oxygen ($O_2$), eventually killing aquatic animals.