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Urea is a useful chemical with many applications including use as a fertilizer.
That you wish to "dispose" of urea implies that there is something
wrong with its specifications that does not allow it to be used on crops. The
most common impurity of synthetic urea is biuret, which impairs plant growth.
The test for biuret is actually a chemical test for proteins and polypeptides
although biuret is neither, but has a peptide bond. You will need to purchase
the biuret reagent, which is a blue solution that turns violet upon contact with
proteins, or any substance with peptide bonds. However, a more practical
approach might be a biological test of applying it to a small test plot and you
can refer to the advice below, for example, do not test it on seedlings. If the
biuret level is too high for plants, the urea can be fed to animals as a source
of nitrogen since biuret is non-toxic to animals.
Agricultural applications of urea: Urea is usually spread at rates of between 40
and 300 kg/ha but rates vary. Smaller applications incur lower losses due to
leaching. During summer, urea is often spread just before, or during rain to
minimize losses from volatilization (process wherein nitrogen is lost to the
atmosphere as ammonia gas). Urea is not compatible with other fertilizers.
Because of the high nitrogen concentration in urea, it is very important to
achieve an even spread. The application equipment must be correctly calibrated
and properly used. Drilling must not occur on contact with or close to seed, due
to the risk of germination damage. Urea dissolves in water for application as a
spray or through irrigation systems. In grain and cotton crops, urea is often
applied at the time of the last cultivation before planting. In high rainfall
areas and on sandy soils (where nitrogen can be lost through leaching) and where
good in-season rainfall is expected, urea can be side- or top-dressed during the
growing season. Top-dressing is also popular on pasture and forage crops. In
cultivating sugarcane, urea is side-dressed after planting, and applied to each
ratoon crop. In irrigated crops, urea can be applied dry to the soil, or
dissolved and applied through the irrigation water. Urea will dissolve in its
own weight in water, but it becomes increasingly difficult to dissolve as the
concentration increases. Dissolving urea in water is endothermic, causing the
temperature of the solution to fall when urea dissolves. As a practical guide,
when preparing urea solutions for fertigation (injection into irrigation lines),
dissolve no more than 30 kg urea per 100 L water. In foliar sprays, urea
concentrations of 0.5% to 2.0% are often used in horticultural crops. Low-biuret
grades of urea are often indicated. Urea absorbs moisture from the atmosphere
and therefore is typically stored either in closed/sealed bags on pallets, or,
if stored in bulk, under cover with a tarpaulin. As with most solid fertilizers,
storage in a cool, dry, well-ventilated area is recommended.
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