Environmental Engineering Reference
In-Depth Information
Table 3.1
Common mineral fertilizers* commercialized in the world.
Nitrogen fertilizers
Ammonia
Ammonium sulphate (AS)
Ammonium nitrate (AN)
Calcium ammonium nitrate (CAN)
Urea
Phosphate fertilizers
Single superphosphate (SSP)
Triple superphosphate (TSP)
Diammonium phosphate (DAP)
Monoammonium phosphate (MAP)
Ground phosphate rock
Potash fertilizers
Muriate of potash (MOP) (potassium chloride)
Sulphate of potash
Sulphate of potash magnesia
Magnesium fertilizers
Kieserite
Epsom salts
Complex fertilizers
NPK fertilizers
NP fertilizers
NK fertilizers
PK fertilizers
K, potassium; N, nitrogen; P, phosphorus.
* The phrase
“mineral fertilizer
is used in the industry to differentiate it from other sources such as manure, legumes, and
other sources of nutrients.
Source
: Adapted from: What are fertilizers? (http://www.fertilizer.org)
needs to be broken to nitrate (NO
3
−
), nitrite (NO
2
−
), or ammonium ion (NH
4
+
) to be available
for plants. The process of transformation of nitrogen to assimilable forms (mainly NH
4
+
) is
called
fixation
and is accomplished via three routes:
1.
Atmospheric fixation by lightning.
2.
Biological fixation by certain specialized microorganisms.
3.
Industrial fixation by means of high temperatures and pressures.
A subsequent reaction,
nitrification
, transforms the ammonium into a nitrate (NO
3
−
). The
opposite reaction, the transformation of assimilable nitrogen into molecular nitrogen (mostly
from NO
3
−
), is named
denitrification
, and when inorganic nitrogen gets combined with carbon,
like that in proteins and nucleic acids, the process is called
immobilization
. To make matters
more complex, the process of nitrification and denitrification is affected by side reactions that
produce nitrous oxide (N
2
O) as a side product (Socolow, 1999). All these chemical reactions are
part of what is called the nitrogen cycle, which was covered in more detail in Chapter 2.
Problems with the alteration of the nitrogen cycle
The nitrogen cycle has been working by
itself and self-regulating since life appeared on Earth. However in the last century, the nitrogen
cycle has been systematically altered by increasing the amount of fixed nitrogen in the soil
with the purpose of sustaining high-yield agricultural crops. Fixed-nitrogen intensification is
accomplished by three different methods:
1.
With ammonia and ammonia derivatives.
2.
By spreading manure.
3.
By cultivation of legumes and other nitrogen-fixing plants.
