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Diammonium phosphate (DAP) is the world’s most widely used
phosphorus fertilizer. It’s made from two common constituents in the
fertilizer industry, and its relatively high nutrient content and
excellent physical properties make it a popular choice in farming and
Ammonium phosphate fertilizers first became available in the 1960s, and
DAP rapidly became the most popular in this class of products. It’s
formulated in a controlled reaction of phosphoric acid with ammonia,
where the hot slurry is then cooled, granulated and sieved. DAP handles
and stores well. The standard nutrient grade of DAP is relatively high,
at 18-46-0, so fertilizer products with lower nutrient content may not
be labeled DAP.
The inputs required to produce one ton of DAP fertilizer are
approximately 1.5 to 2 tons of phosphate rock, 0.4 tons of sulfur (S) to
dissolve the rock, and 0.2 tons of ammonia. Changes in the supply or
price of any of these inputs will impact DAP prices and availability.
The high nutrient content of DAP helps reduce handling, freight and
application costs. DAP is produced in many locations in the world and is
a widely traded fertilizer commodity.
DAP can be applied for all field crops, grassland and in gardens and
orchards. For the best effect DAP should be applied prior to sowing
mixed with soil at the depth of ca. 20cm under the ground. It is
recommended to use it in early Spring mainly for winter crops.
DAP gives optimal effects when applied with potassium chloride with
which it can be mixed at any time. Directly before spreading it can be
also blended with urea, ammonium nitrate and CAN.
DAP fertilizer is an excellent source of P and nitrogen (N) for plant
nutrition. It’s highly soluble and thus dissolves quickly in soil to
release plant-available phosphate and ammonium. A notable property of
DAP is the alkaline pH that develops around the dissolving granule.
As dissolving DAP granules release ammonium, the seedlings and plant
roots nearest the volatile ammonia can be harmed. This potential damage
more commonly occurs when the soil pH is greater than 7, a condition
that often exists around the dissolving DAP granule. To prevent such
damage, users should avoid placing high concentrations of DAP near
The ammonium present in DAP is an excellent N source and will be
gradually converted to nitrate by soil bacteria, resulting in a
subsequent drop in pH. Therefore, the rise in soil pH surrounding DAP
granules is a temporary effect. This initial rise in soil pH neighboring
DAP can influence the micro-site reactions of phosphate and soil organic
DAP also acts as a fire retardant. For example, a mixture of DAP and
other ingredients can be spread in advance of a fire to prevent a forest
from burning. It then becomes a nutrient source after the danger of fire
has passed. DAP is used in various industrial processes, too, such as
metal finishing. And, it’s commonly added to wine to sustain yeast
fermentation and to milk to produce cheese cultures.