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.
Monday, March 18, 2013
Monoammonium phosphate (MAP): A great phosphate fertilizer
MAP : Monoammonium phosphate fertilizer
Monoammonium phosphate (MAP) is a
widely used source of P and N. It is made of two constituents common in the
fertilizer industry and has the highest P content of any common solid
The process for manufacturing MAP
is relatively simple. In a common method, a one to one ratio of ammonia (NH3) and phosphoric acid (H3PO4) is reacted and the
resulting slurry of MAP is solidified in a granulator. The second method is to
introduce the two starting materials in a pipe-cross reactor where the
reaction generates heat to evaporate water and solidify MAP. Variations of
these methods are also in use for MAP production. An advantage of producing MAP
is that lower quality H3PO4can be used compared with other P fertilizers that often
require a more pure grade of acid. The P2O5equivalent content of MAP varies from 48 to 61%, depending
on the amount of impurity in the acid. The most common fertilizer composition
P2O5 range: 48 to 61%
range: 10 to 12%
solubility (20º) 370 g/L
pH 4 to 4.5
Monoammonium fertilizer: one mole of ammonium and one more of phosphate
MAP has been an important granular fertilizer for
many years. It is water soluble and dissolves rapidly in soil if adequate
moisture is present. Upon dissolution, the two basic components of the
fertilizer separate again to release NH4+ and H2PO4-. Both of these nutrients are important to sustain healthy
plant growth. The pH of the solution surrounding the granule is moderately
acidic, making MAP an especially desirable fertilizer in neutral and high pH
soils. Agronomic studies show that there is no significant difference in P
nutrition from various commercial P fertilizers under most conditions.
Granular MAP is applied in concentrated bands beneath
the soil surface in proximity of growing roots or in surface bands. It is also
commonly applied by spreading across the field and mixing into the surface soil
with tillage. In powdered form, it is an important component of suspension
fertilizers. When MAP is made with especially pure H3PO4, it readily dissolves into
a clear solution that can be used as a foliar spray or added to irrigation
water. The P2O5equivalent content of
high-purity MAP is usually 61%.
There are no special precautions associated with the
use of MAP. The slight acidity associated with this fertilizer reduces the
potential for NH3loss to the air. MAP can be placed in close proximity to
germinating seeds without concern for NH3
When MAP is used as a foliar spray or added to
irrigation water, it should not be mixed with calcium or magnesium fertilizers.
MAP has good storage and handling properties. Some of the chemical impurities
(such as iron and aluminum) naturally serve as a conditioner to prevent caking.
Highly pure MAP may have a conditioner added or may require special handling to
prevent clumping and caking. As with all P fertilizers, appropriate management
practices should be used to minimize any nutrient loss to surface or drainage
A high purity source of MAP is used as a feed
ingredient for animals. The NH4+ is synthesized into protein
and the H2PO4- is used in a variety of metabolic functions in animals.
MAP is used in dry chemical fire extinguishers
commonly found in offices, schools, and homes. The extinguisher spray disperses
finely powdered MAP, which coats the fuel and rapidly smothers the flame.
A pdf version of this post is available from the IPNI website here:
Abbreviations and notes: N = nitrogen; P = phosphorus; NH4+ = ammonium; H2PO4- = phosphate. MAP is also known as
ammonium phosphate monobasic, ammonium dihydrogen phosphate