Nitrogen is the most abundant element in fertilisers, which also means the most is required for healthy plant function, and is required in all plants. The main function of nitrogen is to trap energy generated by the photosynthetic process by the way of chlorophyll. It is also a major constituent of protein, a property linked to the quality of seeds, fruits and flowers the plant produces. The air is composed of nearly 80% nitrogen and some plants (for example legumes) are able to take it from the air for immediate use (fixing).
Nitrogen can be lost from the soil in two main ways: leaching and denitrification. Leaching occurs after heavy rain, and the water causes the nutrients to fall below the root level in the soil, meaning the roots can no longer take it up. Denitrification is when the nitrogen returns to the air, by evaporation or is converted to an unusable form of nitrogen by bacteria in the soil. Nitrogen deficiency symptoms include reduced chlorophyll, sugar and protein production and pale green or yellow leaves where the older leaves are impacted first. It can also be seen by stunted growth and poorly developed roots. Urea is the most common form of nitrogen fertiliser, of which Bisley sells BioLow Biuret urea.
Incitec Pivot Fertilisers. (2017). Nitrogen [Ebook]. Retrieved 10 February 2022, from https://www.incitecpivotfertilisers.com.au/~/media/Files/IPF/Documents/Fact%20Sheets/11%20Nitrogen%20Fact%20Sheet.pdf.