MINERAL NITROGEN FERTILIZERS: ENVIRONMENTAL IMPACT OF PRODUCTION AND USE - Fertilizers: Components, Uses in Agriculture and Environmental Impacts - page 26

Evaluation of the Environmental Impact by Means of LCA

During the life cycle of mineral nitrogen fertilizers, greenhouse gas emissions may arise
through the extraction of resources, the transport of raw materials and products, in fertilizer
production processes and during an agronomic phase as N 2 O, NO 3 - , NH 3 and NO x . The
fertilizer industry recognizes that it contributes directly and indirectly to the emission of
greenhouse gases (GHGs), as carbon dioxide (CO 2 ), nitrous oxide (N 2 O) and methane (CH 4 ),
during production, distribution and use of fertilizers (IFA, 2009). In line with international
greenhouse accounting practice (IPCC, 2006), emission factors are expressed as carbon
dioxide equivalents using the ―global warming potential‖ (GWP), which determines the
relative contribution of a gas to the greenhouse effect (Table 8). In particular, the global
GHG emissions can be divided for the following processes: 0.93% from fertilizer production;
0.07% from fertilizer distribution; 1.5% from fertilizer use. Therefore, due to the
environmental relevance of the production phase of fertilizers, the evaluation of this
contribution to GHGs emissions of agricultural processes by Life Cycle Assessment must be
considered (Wood & Cowie, 2004). Several studies have shown that the crop production is
based on the use of input flows directly or indirectly dependent upon the global availability of
the fossil fuels and other minerals, both non-renewable resources, like fertilizers and diesel oil
for agricultural machines (Table 9). The same results was also obtained in case of the
biodiesel production from soybean oil in Brazil (Cavalett & Ortega, 2010) and sunflower
cultivation in Tuscany (Italy) (Spugnoli et al., 2012; Spinelli et al., 2012 and 2013a), and
electricity from willow biomass crop production systems in New York (Heller et al., 2003).
Because production processes are based on fossil fuel, it can be seen in many life cycle
assessment studies that the production of nitrogen fertilizers is one of the major contributors
to greenhouse gas emissions from agriculture production systems. In particular, the basic
component in current industrial nitrogen fertilizer production is ammonia produced by the
Haber-Bosch process (N 2 +3H 2  2NH 3 ). The hydrogen originates from natural gas and the
nitrogen from air (EFMA, 2000a). Furthermore, during the production of nitrate-based
fertilizers, like ammonium nitrate, significant amounts of N 2 O are emitted during the
production of nitric acid. The N 2 O gas emissions from the nitrogen fertilizers feedstocks
could generate effects on climate change higher than to those caused by carbon dioxide
emissions because of the 298 time greater global warming potential (Forster et al., 2007;
Brentrup et al., 2001; Spinelli et al., 2013b). On the other hand, in the urea plant, the carbon
dioxide emissions are high with respect to nitrate-based fertilizers plant and carbon dioxide is
re-used in the synthesis phase (European Commission, 2006). However, a switch to urea or
another non-nitrate fertilizer would lead to higher contributions to acidification and
eutrophication (Brentrup et al., 2001).
Table 8. Global Warming Potential relative to CO 2 equivalents for greenhouse gases
emissions (Solomon et al., 2007)

Chemical
formula

Global Warming Potential for Given
Time Horizon

Common name

20 - yr 100 - yr 500 - yr

Carbon dioxide CO 2 1 1 1

Methane CH 4 72 25 7.6