Urea’s introduction and scientific invention is deemed as a life changing event and turning point in the history of agriculture. It constitutes the most commonly used nitrogen fertilizer across all agricultural lands of the world. Its usage has led to a booming height in both production and prosperity. During the last decade, urea has been rapidly replacing ammonium nitrate to unleash new unsurpassed production records.
This white crystalline solid is an inexpensive form of nitrogen fertilizer with a proportionate compound mixture, i.e. NPK (nitrogen-phosphorus-potassium) ratio of 46-0-0. This implies that the mixture has 46% nitrogen. Even though urea is naturally produced in humans and animals, the manufacture of synthetic urea is done with anhydrous ammonia.
Urea has the chemical formula as NH2)2CO. Its molecule has two —NH2 groups joined by a carbonyl (C=O) functional group. This scientific organic compound is known as carbamide. The name was coined by the International Nonproprietary Name (rINN). Its other popular names are carbamide resin, carbonyldiamine and isourea, carbonyl diamide.
It is the first organic compound which was artificially synthesized through chemical processes with the help of inorganic compounds. Friedrich Wohler did it in1828 and was left stunned at his discovery. His conclusion that potassium cyanate when treated with ammonium sulfate produced urea initiated the start of the organic revolution. Urea is a soluble compound and easily gets along with water.
Commercially, urea is produced using two basic raw materials,- ammonia and carbon dioxide. Here, the carbon dioxide gas is made to react with anhydrous ammonia under intense pressure, at 350 degrees Fahrenheit. Urea is then processed to form granules or solid globules known as prills. For it, molten urea is sprayed down a tower, up which air is pumped. Being slightly smaller than Urea granules sold in market, these are especially beneficial when the fertilizer is being applied to the plants by hands. It’s important to note that huge quantities of carbon dioxide are produced when ammonia is being manufactured from coal or from hydrocarbons like natural gas and other petroleum derived raw materials. This facilitates direct synthesis of urea from the raw materials. Precaution should be taken to keep dry urea away from moisture until its use as it is extremely soluble. Apart from prills and granules, it is also produced as pellets, flakes, crystals and solutions.
Apart from being widely used as a fertilizer and animal feed, urea has widespread uses in various other industries. Some of them are –
- It is used as raw material for the manufacture of plastics, specifically urea-formaldehyde resin as well as for manufacture of various waterproof glues used for marine plywood.
- It is preferred over rock salt in the deicing of roadways and runway since it provides better blocking of metal corrosion.
- As an additive ingredient, it enhances flavor in cigarettes.
- Occasionally used as a browning agent in factory-produced pretzels.
- It’s an integral ingredient of some cosmetics like hair conditioners, facial cleansers, bath oils etc.
- It is the reactant in some ready-to-use cold compresses for first-aid use.
- For diesel engine exhaust treatment AdBlue and other SCR systems, it is a very active ingredient.
- Used as flame-proofing agent.
- A clean burning fuel for motor vehicles and stationary engines.
- Widely used as a NOx-reducing reactant in diesel exhaust.
How to use urea nitrogen as fertilizer
Urea can be applied to the soil as solid granules, prills or pellets. Granules are most popular today since they are larger, harder, and more stable under high humidity. They can be dissolved in water and the soil drenched with it or distributed with irrigation water or applied as foliar spray.
After application to the soil, urea combines with water through hydrolysis process to form ammonium carbonate [(NH4)2CO3] with the help of the catalytic action of urease, an enzyme present and produced in the soil by the decomposition of organic matter by microorganisms. The formed compound is unstable and decomposes into ammonia gas, carbon dioxide and water. If not adequately protected, the ammonia gas can be lost to the environment. Hence it’s important to mix urea well with soil for maximum effectiveness either by broadcasting the urea before plowing it into the soil immediately or by injecting the urea into the soil. Ammonia gas now combines with hydrogen ion (H+) from soil to form positively charged ammonium ions (NH4+). These then get fixed into the negatively charged soil particles and stay so till absorbed by plants through roots or converted to nitrate due to the bacterial action in the soil.
As a general urea should never be applied on soil surface but incorporated into soil to block ammonia gas loss, referred to as ammonia volatilization. The urea fertilizer can be applied single or by mixed with other fertilizers like sulphate of potash, calcium cyanamide or sulphate of potash magnesia. However, the mixed fertilizers should not be stored for more than 2-3 days. Additionally there are some fertilizers which should not be mixed with urea. Some of them are calcium ammonium nitrate, calcium nitrate, ammonium sulphate nitrate, nitropotash, superphosphate, and triple superphosphate.
The urea fertilizer is extremely popular for a variety of reasons. Some of its major advantages are –
- Urea provides the highest nitrogenous content for plants amongst all nitrogenous fertilizers available today at the lowest possible cost.
- The fertilizer comes very cheap as its cost of production is relatively low. Thus it is highly preferred in developing countries.
- Transporting the fertilizer is easy as it is least likely to ‘cake’.
- Very easy to store, it does not carry any risk of catching fire or explosion hazards for long-term storage.
- It can be used exclusively or in safe combination with a wide array of fertilizers. It is the best fertilizer for acidifying soils and for heavy nitrogen feeder crops like strawberries, corn, blueberries etc.
- It can be used for all types of crops and soils with no harm to the soil.
Precautions with the Urea Nitrogen Fertilizer
Some precautionary steps to be adhered to when handling the urea fertilizer are –
- Its packaging has to be top class since it is highly soluble in both water and hygroscopic water.
- During storage, it is mandatory to maintain extremely dry conditions for the same reason.
- It is unstable in comparison to other solid nitrogenous fertilizers and decomposes even at room temperatures, leading to serious loss.
- Urea with impurities above 2 percent cannot be used as a fertilizer as they may prove toxic to certain crops, particularly citrus.
- Owning to the chemical reaction following the application of urea to soil, chances of nitrogen loss through ammonia volatilization is very high, which can make using urea fertilizer, an impractical option for farmers with large plots of land. Proper application is imperative.
Due to its high nitrogen content and its neutral ability to adapt to all kind of land and soil, it is no wonder that the urea fertilizer is known as the king of fertilizers. The fertilizer is truly and rightfully responsible for the huge success in agro revolution. The fertilizer is yet to find its match.