by Granular urea, also known simply as urea or carbo-nitrogen, is a fertilizer which has seen increasing use over the past few decades. Made from ammonia and carbon dioxide, granular urea delivers nitrogen to plants in a soluble and efficient form. Let’s take a closer look at this important fertilizing agent.
Introduction to Granular Urea
Urea was first synthesized in 1828 by the German chemist Friedrich Wöhler. It soon became apparent that urea could serve as a nitrogen-rich fertilizer for plants. However, it wasn’t until the mid-20th century that urea began to be produced on an industrial scale. This coincided with a rise in demand for nitrogen fertilizers needed to support the world’s growing population through increased agricultural yields.
Granular Urea builds upon the basic urea molecule by converting it into solid prills or granules between 1-5 mm in diameter. This process, known as granulation, makes the urea much easier for farmers to handle and apply compared to its powdered form. Granulation also slows the dissolution rate of urea in soil, allowing it to provide a steady supply of nitrogen to plants over several weeks. For these reasons, granular urea has become the predominant type used worldwide in commercial agriculture.
Composition and Nutrient Content
Chemically, granular urea is composed of 46% nitrogen. All of this nitrogen is in the ammonium (NH4+) form right after application. However, urease enzymes present in the soil rapidly hydrolyze the urea into ammonium carbonate, which then decomposes further into ammonium (NH4+) and carbon dioxide (CO2).
Plants cannot absorb or utilize nitrogen in its urea or carbonate forms. They can only uptake the ammonium ion once it is produced through hydrolysis. A single pound of granular urea contains 0.462 pounds or 0.46 units of plant-available nitrogen. Most recommendations are to apply urea at a rate of 1-1.5 pounds of actual nitrogen per 1000 square feet of lawn or garden area.
Advantages of Granular Urea
There are several reasons why granular urea has become such a dominant nitrogen fertilizer used by farmers around the world:
Convenience – As mentioned, granules are far easier for mechanical spreaders to handle compared to powdered urea. They also present less risk of volatilization losses into the air.
Efficiency – Urea delivers nitrogen to plants in a readily absorbable ammonium form through natural soil hydrolysis. Up to 95% of its nitrogen can be taken up by plants in one growing season.
Cost Effectiveness – Urea has a high nitrogen content of 46% and remains one of the most affordable nitrogen fertilizers per pound of actual nitrogen. This makes it very cost effective for large-scale agricultural uses.
Stability – When properly stored, granular urea maintains its nutrient content and effectiveness for several years without breaking down. This stability during transport and storage is ideal.
Slow Release – The granule coating delays but does not prevent hydrolysis. This allows nitrogen to be released gradually over 1-3 months as plants need it, reducing leaching losses.
Potential Drawbacks of Granular Urea
While very effective as a nitrogen source, granular urea does have some potential drawbacks to be aware of:
Volatilization – On hot days, a small percentage (typically less than 10%) of the urea nitrogen can be lost through conversion to ammonia gas and evaporation if not watered-in promptly after application.
Leaching – In sandy, poorly drained soils or after heavy rainfall, some of the mobile ammonium ions may leach below the plant root zone before being taken up. Proper application timing can help minimize this.
Burning – If over-applied, the high concentration of nitrogen can burn turf and plant foliage. Rates should not exceed 1-1.5 lbs of N per 1000 sq ft except in divided applications.
Runoff Risk – Surface granules washed into lakes or streams during storms could potentially contaminate water sources. Sweep any granules off paved areas.
In summary, when properly used at recommended rates and timed with adequate irrigation, granular urea fertilizer remains one of the most cost-effective sources of nitrogen for productive soils. Its widespread adoption globally is a testament to both its agronomic benefits and its importance for sustainably feeding our growing population. With responsible management practices, its drawbacks can largely be avoided as well.
