Agriculture Reference
In-Depth Information
Snapp et al., 2005; Syswerda et al., 2012). Similarly, Fageria (2009) also reported that adopting
adequate nitrogen fertilizer management practices can produce higher crop yields and conse-
quently improves nitrogen use efficiency. These practices include the use of an effective source
of nitrogen, the use of appropriate methods of nitrogen application, the use of adequate rates,
the adoption of appropriate timing of nitrogen application, the use of nitrification inhibitors, and
foliar fertilization.
8.3.1 u
se
of
an
e
ffeCtIve
s
ourCe
of
n
ItroGen
The use of an effective source is fundamental in improving N use efficiency and consequently reap-
ing a higher yield of crops. There are several sources of nitrogen. Major N fertilizers available in the
world market along with their N contents are presented in Table 8.6. Urea and ammonium sulfate
are the main nitrogen carriers worldwide in annual crop production. However, urea is generally
favored by the growers over ammonium sulfate due to the lower application cost because urea has
a higher N analysis than ammonium sulfate (46% vs. 21% N). Tisdale et al. (1993) reported that
the most cost-effective granular form of N is urea [CO(NH
2
)
2
] as it has a high N concentration and
lower relative manufacturing, handling, storage, and transportation costs. Once applied to the soil,
urea is hydrolyzed by the enzyme urease to ammonia N (
NH
3
−
), which temporarily creates a high
concentration of
NH
3
−
, and then converts into ammonium N (
NH
4
+
). The conversion from
NH
3
−
into
NH
4
+
can be delayed by dry soil conditions or coarse-textured soils, which increases the potential
for volatilization in wet, windy conditions, or phytotoxicity to seeds and plants when seed-placed
(Tisdale et al., 1993).
In developed countries like the United States, anhydrous NH
3
is an important N source
for annual crop production. At normal pressures, NH
3
is a gas and is transported and handled
as liquid under pressure. It is injected into the soil to prevent loss through volatilization. The
NH
3
protonates to form
NH
4
+
in the soil and becomes
XNH
4
+
,
which is stable (Foth and Ellis,
1988). The major advantages of anhydrous NH
3
are its high N analysis (82% N) and low cost
of transportation and handling. However, specific equipment is required for storage, handling,
TABLE 8.6
Major Nitrogen Fertilizers, Their Chemical Formulas, and N Contents
Common Name
Formula
N (%)
Ammonium sulfate
(NH
4
)
2
SO
4
21
Urea
CO(NH
2
)
2
46
Anhydrous ammonia
NH
3
82
Ammonium chloride
NH
4
Cl
26
Ammonium nitrate
NH
4
NO
3
35
Potassium nitrate
KNO
3
14
Sodium nitrate
NaNO
3
16
Calcium nitrate
Ca(NO
3
)
2
16
Calcium cyanamide
CaCN
2
21
Ammonium nitrate sulfate
NH
4
NO
3
(NH
4
)
2
SO
4
26
Nitrochalk
NH
4
NO
3
+ CaCO
3
21
Monoammonium phosphate
NH
4
H
2
PO
4
11
Urea ammonium nitrate
32
CO(NH
2
)
2
+ NH
4
NO
3
Diammonium phosphate
(NH
4
)
2
HPO
4
18
Source:
From Fageria, N. K. 2009.
The Use of Nutrients in Crop Plants
. Boca Raton, Florida:
CRC Press. With permission.
