Fertilizers are responsible for over half of global food production, but there are areas in world with nutrient deficiency and other areas of nutrient excess.
Managing mineral plant nutrients requires careful application of science and skill to meet production, environmental, and social goals.
Thursday, October 4, 2012
Ammonium Nitrate as a Fertilizer
Young corn field
Ammonium nitrate was the first
solid nitrogen (N) fertilizer produced on a large scale, but its popularity has
declined in recent years. It has been a common N source because it contains
both nitrate and ammonium and it has a relatively high nutrient content.
Large-scale production of
ammonium nitrate began in the 1940s when it was used for munitions during
wartime. After the end of World War II, ammonium nitrate became available as a
commercial fertilizer. The production of ammonium nitrate is relatively simple,
where ammonia gas is reacted with nitric acid to form a concentrated solution
and considerable heat.
Prilled fertilizer is formed
as a drop of the concentrated ammonium nitrate solution (95 to 99%) falls from
a tower and solidifies. Low density prills are more porous than high density
prills and are preferred for industrial use, while high density prills are used
as fertilizer. Granular ammonium nitrate is made by repeatedly spraying the
concentrated solution onto small granules in a rotating drum.
Since ammonium nitrate is
hygroscopic and readily attracts moisture from air, it is commonly stored in
air-conditioned warehouses or in sealed bags. The solid fertilizer is usually
coated with an anti-caking compound to prevent sticking and clumping.
Fertilizer going into storage
Small quantities of carbonate
minerals are sometimes added prior to solidifying, which eliminates the
explosive properties of ammonium nitrate. These additives lower the N
concentration and are sparingly soluble, making the modified product less
suitable for application through an irrigation system (fertigation).
Chemical formula: NH4NO3
Composition: 33 to 34% N
Water solubility (20 ºC):
Ammonium nitrate is a popular
fertilizer since it provides half of the N in the nitrate form and half in the
ammonium form. The nitrate form moves readily with soil water to the roots
where it is immediately available for plant uptake. The ammonium fraction is
taken up by roots or gradually converted to nitrate by soil microorganisms.
Many vegetable growers prefer an immediately available nitrate source of plant
nutrition and use ammonium nitrate. It is popular for pasture and hay
fertilization since it is less susceptible to volatilization losses than
urea-based fertilizers when left on the soil surface.
Ammonium nitrate is commonly
mixed with other fertilizers, but these mixtures cannot be stored for long
periods because of a tendency to absorb moisture from the air. The very high
solubility of ammonium nitrate makes it well suited for making solutions for
fertigation or foliar sprays.
Ammonium nitrate is a popular
N fertilizer due to its ease of handling and high nutrient content. It is very
soluble in the soil and the nitrate portion can move beyond the root zone under
wet conditions. Nitrate can also be converted to nitrous oxide gas in very wet
conditions through the process of denitrification. The ammonium portion is not
subject to considerable loss until it is oxidized to nitrate.
Concerns over illegal use of
the fertilizer for explosives have caused strict government regulation in many
parts of the world. Restrictions on sales and transportation have caused some
fertilizer dealers to discontinue handling this material.
A low-density form of prilled
ammonium nitrate is widely used as an explosive in the mining industry, for
quarries, and in construction sites. It is intentionally porous to allow rapid
adsorption of fuel oil (termed ANFO).
Instant cold packs are made
with two bags—one containing dry ammonium nitrate and the second containing
water. When the barrier separating the bags is ruptured, the ammonium nitrate
rapidly dissolves in an endothermic reaction, lowering the pack’s temperature
to 2 to 3 ºC within a very short time.