Agriculture Reference
In-Depth Information
Rochette et al., 2008). Studies showed that up to 60% of applied fertilizer N could be lost through
NH
3
volatilization in flooded rice soils (Xing and Zhu, 2000), depending on the type of N fertilizer,
tillage practices, and soil properties (temperature and pH) (Duan and Xiao, 2000; Gioacchini et al.,
2002; Hayashi et al., 2011; Zhang et al., 2011). The gaseous ammonia in the atmosphere can cause
environmental problems such as soil acidification and changes in biodiversity (Eerden et al., 1998;
Stevens et al., 2004; Emmett, 2007; Xu et al., 2013).
Ammonia volatilization represents an agronomic N loss with NO
x
and SO
x
creates particulate
2.5-µm aerosols that scatter light, resulting in haze (Asman et al., 1998; Sharma et al., 2007). Several
studies have been conducted to estimate N loss through NH
3
-N volatilization from inorganic N
fertilizers applied to agricultural lands (Wang et al. 2004; Pacholski et al., 2006). The economic
impact associated with NH
3
-N emission from N fertilizers applied to agricultural land is estimated
at U.S. $11.6 billion annually worldwide (FAO/IEF, 2001). Ammonia volatilization also causes
serious climatic and environmental problems (Gay and Knowlton, 2005). In addition, the emitted
NH
3
-N exacerbates global climate change (Singh et al., 2012a,b). Although the reaction of NH
3
-N
with OH radicals is relatively slow, the intermediate NH
2
radical can provide a substantial nitrous
oxide (N
2
O) source, thus contributing to the production of N
2
O, one of the major greenhouse gases
(GHGs) (Finlayson-Pits and Pitts, 2000). Dentener and Crutzen (1994) estimated that 4% (3 × 10
6
MT N year
−1
) of the globally emitted NH
3
-N can be oxidized by OH radicals to N
2
O, mainly in the
tropics. The redeposition of NH
3
-N in nonagricultural soils can also lead to acidification (Singh
et al., 2012a,b). Therefore, it is important to identify and select N sources with minimal NH
3
-N
losses to safeguard environmental quality and reduce crop production costs (Singh et al., 2012a,b).
Ammonium volatilization can be expressed by the following equation (Bolan and Hedley, 2003):
NH
+
+ ⇔+
OH
NH
HO
4
3
2
Ammonia volatilization from flooded rice soils is a major mechanism for N loss and a cause of
low fertilizer use efficiency by rice. Reviews on NH
3
volatilization from flooded rice soils indicate
that losses of ammonical-N fertilizer directly applied to floodwater may vary from 10% to 50% of
the amount applied (Fillery and Vlex, 1986; Mikkelsen, 1987). Losses, however, are site and soil
management specific; thus, disparities may exist in reported rates of volatilization, depending on
rate-controlling factors and methods of measurement. Ammonia volatilization under flooded rice
conditions is influenced by five primary factors: NH
4
-N concentration, pH, temperature, depth of
flooded water, and wind speed (Jayaweera and Mikkelsen, 1990; Fageria and Gheyi, 1999).
Volatilization losses from surface applications of urea-containing N sources can be related to
soil and weather conditions following the application. Fox and Hoffman (1981) categorized NH
3
volatilization losses in Pennsylvania based on the rainfall amount and the length of time between
surface application and rainfall. They concluded that 10 mm of rain accruing within 2 days after
surface N application resulted in no NH
3
volatilization losses. The losses increased with increased
time between application and rain and are substantial (>30%) if no rain falls within 6 days. Urban
et al. (1987) reported that maximum NH
3
losses from surface-applied urea in a growth chamber
occurred between 4 and 8 days after application.
Urea is the principal source of N for crop production around the world because of its high N
content (46%), low relative cost, ease in handling, and compatibility with other fertilizer materials
(Kissel et al., 2009). Ammonia volatilization occurs when urea is hydrolyzed in the presence of
water and urease to form NH
4
(Torello et al., 1983; Kissel and Cabrera, 1988). The hydrolysis of urea
can be expressed by the following equation (Fageria et al., 2010):
CO
(NH
22
+ ⇔+
3H O
2
H OH
+
−
+
CO
2
4
2
NH
+
+ ⇔+
2O
NO
−
2H
+
+
HO
4
2
3
2
