Nitrification is a biological process in which soil microorganisms convert ammonium nitrogen (NH₄⁺) into nitrite (NO₂⁻) and subsequently into nitrate (NO₃⁻). This transformation is carried out by specialised microorganisms, including nitrifying bacteria and archaea, which convert ammonium nitrogen into forms that are more readily available for plant uptake. Nitrate is the primary form of nitrogen absorbed by many plants due to its high availability for root uptake. Nitrification is an essential component of the soil nitrogen cycle and plays a key role in regulating nitrogen availability for plants.
Nitrification inhibitors are substances added to fertilisers containing ammonium nitrogen or to organic fertilisers, such as slurry, to slow down the process of nitrification in the soil. Their application reduces the rate at which ammonium nitrogen (NH₄⁺) is converted into nitrite (NO₂⁻) and subsequently nitrate (NO₃⁻). This allows ammonium nitrogen to remain in the soil for a longer period in a form that is less susceptible to leaching, thereby reducing the risk of nitrate losses to groundwater. Nitrification inhibitors improve nitrogen use efficiency and contribute to reducing the environmental impacts associated with agricultural production.
Nitrogen (N) is the primary plant macronutrient and plays a fundamental role in plant growth and development. It is an essential component of proteins, enzymes, nucleic acids, and other organic compounds involved in plant metabolism. Nitrogen has the greatest influence on crop productivity and is often regarded as the principal driver of vegetative growth. Plant nitrogen requirements are commonly determined using the Nmin method, which measures the amount of plant-available mineral nitrogen present in the soil. Typical symptoms of nitrogen deficiency include pale green leaves, chlorosis of older leaves, reduced plant growth, and a stiff growth habit accompanied by poorly developed foliage.
The nitrogen cycle describes the transformation of nitrogen from one form to another as it circulates between the atmosphere, soil, plants, and animals. Atmospheric nitrogen (N₂) is fixed by certain microorganisms and converted into ammonia (NH₃) and other plant-available forms of nitrogen. Plants absorb nitrogen primarily as ammonium (NH₄⁺) and nitrate (NO₃⁻) ions from the soil, while animals obtain nitrogen through their diet. Following the death of organisms and the deposition of organic residues, soil microorganisms decompose organic matter and return nitrogen to the soil. Through the process of denitrification, excess nitrogen may be converted back into molecular nitrogen (N₂), which is released into the atmosphere.
Nutrient absorption is a physiological process through which plants take up nutrients from the soil solution via the root system or, in the case of foliar application, through the leaves. The efficiency of nutrient absorption depends on nutrient availability, soil pH, moisture, temperature, and root development.
Nutrient use efficiency (NUE) describes the relationship between the amount of nutrients supplied to plants through organic or mineral fertilisation and the amount of nutrients that plants actually absorb and utilise. High nutrient use efficiency means that nutrient losses through soil fixation or leaching are minimised, allowing plants to efficiently take up and use nutrients for growth and development. Improving nutrient use efficiency contributes to more sustainable agricultural production, reduces environmental impacts, and increases the economic efficiency of fertiliser use. Naturally occurring bioactive substances in fertilisers may further enhance nutrient availability and nutrient use efficiency.
