Urea is an organic compound (containing carbon atoms), found in plants, animals and soils, and is a breakdown product from the metabolism of proteins. Urea is also called carbamide, in that it has two amino groups (-NH2) bonded to a carbonyl functional group (-C(=O)-), to form CO(NH2)2.
Urea is not involved in metabolic processes; however it has a high nitrogen content that is recycled by the breakdown to ammonium (NH4+), nitrate (No3-) which may be metabolised, and Co2.
The energy demanding process is catabolised by the enzyme Urease, which is produced by specific bacteria and some plants. The nitrogenous molecules are then recycled or absorbed by bacteria and plants and used in the construction or participation within nitrogen required processes, and thereby completing the nitrogen cycle.
Urea can also be manufactured synthetically, through the reaction of natural gas, atmospheric nitrogen and water at high temperatures and pressure, to produce ammonia and carbon dioxide. The gases are further reacted under pressure and at high temperatures to produce molten urea, then refined to crystalline urea. The process is very energy intensive.
From the farming perspective, there are two useful sources of urea, namely Natural Urea and Synthetic Urea. Whilst the chemical structures are identical, Natural Urea is found in very low quantities and are in balance with the soil biota and importantly, is bound to other organic structures providing a ‘bank’ of exchangeable nitrogen for plants and bacteria.
Synthetic Urea is a refined crystalline material that when added to water undergoes complex chemical changes that may involve Urease or alternative hydrolytic processes. Modern organic chemistry is developing processes and techniques that improve the efficiency of synthetic urea.
Interestingly, Certified Organic Farming does not allow for the use of synthetic urea as the requirements of Organic Certification restricts the use of inputs to natural products or extracts from natural products. Crystalline urea does not meet this requirement.
Prepared by J H McKay for ECTOL Plant and Crop Nutrients. Last updated, March 2024.
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