Urea fertilizer... the basics
Urea is the most widely used solid N
fertilizer in the world. Urea is also commonly found in nature since it is
expelled in the urine of animals. The high N content of urea makes it efficient
to transport to farms and apply to fields.
Production
The production of urea fertilizer involves controlled reaction of
ammonia gas (NH3) and carbon
dioxide (CO2) with
elevated temperature and pressure. The molten urea is formed into spheres with
specialized granulation equipment or hardened into a solid prill while falling
from a tower.
During the production of urea, two urea molecules may
inadvertently combine to form a compound termed biuret, which can be damaging
when sprayed onto plant foliage. Most commercial urea fertilizer contains only
low amounts of biuret due to carefully controlled conditions during
manufacturing. However, special low-biuret urea is available for unique
applications.
Urea manufacturing plants are located
throughout the world, but most commonly located near NH3
production facilities since NH3
is the major input for urea. Urea is transported throughout the
world by ocean vessel, barge, rail, and truck.
Chemical Properties
Chemical Formula: CO(NH2)2
N content: 46% N
H2O
Solubility (20ยบC): 1,080 g/L
Agricultural Use
Urea is
used in many ways to provide N nutrition for plant growth. It is most commonly
mixed with soil or applied to the soil surface. Due to the high solubility, it
may be dissolved in water and applied to soil as a fluid, added with irrigation
water, or sprayed onto plant foliage. Urea in foliar sprays can be quickly
absorbed by plant leaves.
After
urea contacts soil or plants, a naturally occurring enzyme (urease) begins to
quickly convert the urea back to NH3 in a process called hydrolysis.
During this process, the N in urea is susceptible to undesirable gaseous losses
as NH3. Various management techniques can be used to minimize the
loss of this valuable nutrient.
Urea hydrolysis is a rapid
process, typically occurring within several days after application. Plants can utilize small amounts of urea
directly as a source of N, but
they more commonly use the
ammonium (NH4+) and nitrate (NO3-)
that are produced after urea is transformed by urease and soil microorganisms.
Management Practices
Urea is an excellent nutrient source to meet the N demand of
plants. Because it readily dissolves in water, surface-applied urea moves with
rainfall or irrigation into the soil. Within the soil, urea moves freely with
soil water until it is hydrolyzed to form NH4+. Care should be used to minimize
all N losses to air, surface water, and groundwater. Avoid urea applications
when the fertilizer will remain on the soil surface for prolonged periods of
time. Undesired N losses may also result in loss of crop yield and quality.
Urea is a high N-containing fertilizer that has good storage
properties and causes minimal corrosion of application equipment. When properly
managed, urea is an excellent source of N for plants.
Non-agricultural Use
Urea
is commonly used in a variety of industries. It is used in power plants and
diesel exhaust systems to reduce emission of nitrous oxide (NOx)
gases. Urea can be used as a protein supplement in the diet of ruminant
animals, such as cattle. Many common industrial chemicals are made using urea
as an important component.
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