As most parts of Zimbabwe recently received incessant rains, Urea
fertiliser presents a good option for effective top-dressing. This is due to
the fact that the conventional nitrogen source Ammonium Nitrate generally
leaches under incessant rainfall which is not the case with Urea. This article
provides basic information concerning Urea and its characteristics. The
objective is for farmers to fully appreciate the nature of Urea and its
effects, and secondly, to assist farmers with the proper use and application of
Urea in maize specifically.
Basic
Description of Urea Fertilizer
Urea is a white crystalline solid fertilizer containing 46% nitrogen.
It is widely used in the agricultural industry as a fertilizer or an animal
feed additive. Here, we only discuss its use as a nitrogen top dressing
fertilizer. Commercially, Urea fertilizer can be purchased as prills or as a
granulated material. In the past, it was usually produced by dropping liquid
Urea from a "prilling tower" while drying the product. The prills
formed a smaller and softer substance than other materials commonly used in
fertilizer blends. Today, Urea is largely manufactured as granules. Granules
are larger, harder, and more resistant to moisture. As a result, granulated
Urea has become a more suitable material for fertilizer blends.
Advantages of Urea Fertilizer:
1. Urea can be
applied to soil as a solid, or solution, or to certain crops as a foliar spray.
2. Urea usage
involves little or no fire or explosion hazard.
3. Urea's high
nitrogen analysis, (46% N) helps reduce handling, storage and transportation
costs over other dry nitrogen forms.
4. Urea
manufacture releases few pollutants to the environment.
5. Urea, when
properly applied, results in crop yield increases equal to other forms of
nitrogen.
Urea
Application Method for Optimal Crop Response
Nitrogen from Urea can be lost to the atmosphere through
volatilization (gaseous) if the fertilizer remains on the soil surface for
extended periods of time in warm weather. The key to the most efficient use of
Urea is to incorporate it into the soil during with a tillage operation. Urea
must be covered by soil immediately unless there is sufficient moisture for it
to immediately dissolve into the soil to avoid volatilization losses. It may
also be blended into the soil with irrigation water. A rainfall of as little as
6 inches/154mm is sufficient to blend Urea into the soil to a depth at which
ammonia losses will not occur.
Urea Losses to
Air
Urea breakdown begins as soon as it is applied to the soil. If the
soil is totally dry, no reaction happens. But with the enzyme Urease, plus any
small amount of soil moisture, Urea normally hydrolyses and converts to ammonia
gas and carbon dioxide. This can occur in 2 to 4 days, and happens quickly on
high pH soils. Unless it rains, Urea must be incorporated during this time to
avoid ammonia loss. Losses might be quite low in the spring if the soil
temperature is low. Urea must always be applied under moist soil conditions.
-
Dr L.T. Gono
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