Plants require essential nutrients for healthy growth, and ammonium salts (e.g., ammonium nitrate, ammonium sulfate) and nitrates (e.g., potassium nitrate) provide key elements for this. Plants absorb nitrogen in the form of ammonium ions (NH₄⁺) and nitrate ions (NO₃^-) from the soil.

Nitrogen is a crucial component of amino acids, proteins, nucleic acids (DNA and RNA), and chlorophyll. It's essential for building plant tissues and promoting vegetative growth (leaves and stems). A deficiency in nitrogen leads to stunted growth and yellowing of leaves (chlorosis).

Ammonium salts provide a readily available source of nitrogen. The ammonium ion (NH₄⁺) can be directly assimilated by plants. However, soil conditions (pH) can affect the availability of ammonium. In alkaline soils, ammonium can be lost as ammonia gas (NH₃), reducing its effectiveness. Nitrates are generally more stable in alkaline conditions.

Nitrates are also readily absorbed by plants and are converted to ammonium ions within the plant. They are particularly important for rapid growth and the development of green foliage.

Therefore, the use of ammonium salts and nitrates as fertilizers ensures plants have an adequate supply of nitrogen, promoting healthy growth and increased crop yields.

While nitrogen-based fertilizers are essential for boosting crop yields, excessive use can lead to several negative environmental consequences. The excess nitrogen that is not absorbed by plants can enter the environment and cause pollution.

Two specific examples of these negative consequences are:

1. Eutrophication: Excess nitrogen and phosphorus from fertilizers can run off into rivers, lakes, and coastal waters. This leads to an overgrowth of algae (algal blooms). When these algae die and decompose, the decomposition process consumes large amounts of oxygen in the water. This oxygen depletion (hypoxia) can kill fish and other aquatic organisms, creating "dead zones."
2. Greenhouse Gas Emissions: The production and use of nitrogen fertilizers contribute to greenhouse gas emissions. The Haber-Bosch process, used to produce ammonia for fertilizers, is energy-intensive and relies heavily on fossil fuels, releasing carbon dioxide (CO₂). Furthermore, nitrogen fertilizers can lead to the emission of nitrous oxide (N₂O), a potent greenhouse gas, from the soil.

Therefore, it is important to use nitrogen fertilizers judiciously and implement sustainable agricultural practices to minimize their environmental impact. This includes using the right amount of fertilizer, applying it at the right time, and employing methods to reduce runoff.

The student's statement is incorrect because NPK fertilisers primarily provide macronutrients – nitrogen (N), phosphorus (P), and potassium (K) – not a wide range of micronutrients. Micronutrients are required in much smaller quantities by plants, but are still essential for various metabolic processes. NPK fertilisers typically do not contain significant amounts of micronutrients like iron, manganese, zinc, or copper.

Nitrogen (N) is essential for the synthesis of proteins, nucleic acids (DNA and RNA), and chlorophyll. It promotes vegetative growth, leading to healthy leaf development and increased biomass. Nitrogen deficiency results in stunted growth and chlorosis (yellowing of leaves).

Phosphorus (P) is crucial for energy transfer within the plant, as it is a component of ATP. It also plays a vital role in root development, flowering, and seed formation. Phosphorus deficiency leads to poor root growth, delayed flowering, and reduced fruit/seed production.

Potassium (K) regulates water balance in the plant by influencing stomatal opening and closing. It also activates enzymes involved in carbohydrate metabolism and enhances disease resistance. Potassium deficiency causes weakened stems, scorching of leaf margins, and reduced overall plant vigour.

In summary, while micronutrients are important, NPK fertilisers are specifically designed to provide the three macronutrients – nitrogen, phosphorus, and potassium – that are required in the largest quantities for optimal plant growth and development.