Page 65 - Materials Chemistry, Second Edition

The Application of Life Cycle Assessment on Agricultural 51

machinery used during crop establishment and husbandry but also for the main-
tenance of livestock housing) and indirectly (i.e., in the form of manufactured
mineral fertilizers and pesticides but also as embodied energy in machinery and
human labor) (Korres 2013). The level of energy consumption and GHG emissions
depends mainly on the production system (e.g., organic or conventional) but also
on the product mix (e.g., the mix of crops and livestock and/or bioenergy pro-
duction). It has been shown, for example, that abandonment of fossil fuel-derived
nitrogen and synthetic pesticides in organic farming consumes less energy and
consequently contributes less to GHG gas emissions than conventional agriculture
(Carlsson-Kanyama 1998; Pimentel and Pimentel 2003; Wallen et al. 2004; Weber
and Matthews 2008).
Besides the approach to input use, soil management practices, such as tillage,
irrigation, use of cover crops (Mummey et al. 1998) in cropping systems and
storage of slurries and manures in livestock systems, influence GHG gas emis-
sions. In the context of choice of the cropping system, crop rotation has a strong
influence on emissions. For example, adapting crop rotations to include more
perennial crops, thereby avoiding use of bare and fallow land, reduces GHG gas
emissions from agriculture by accumulating soil carbon stocks (Smith et al. 2007).
When multiple-cropping systems are practiced either as sequential cropping or
intercropping (Korres 2005), the issue of land use, which is one of the most
fundamental factors that influences directly (e.g., tillage) or indirectly (e.g., by the
collection of crop residues to be used for biogas or bioethanol production) carbon
stocks arises. Cultivation, generally leads to reduction in soil organic carbon (Reay
and Grace 2007) which, without counteracting husbandry practices such as winter
cover crops (Rajagopal and Zilberman 2007), is exacerbated by crop residues
removal, e.g., corn stover (Wilhelm et al. 2004) (Fig. 9).
A number of management practices are available to increase soil carbon inputs
in croplands through the use of crop rotations with high residue yields, or reducing
the gap between successive crops in annual crop rotations (i.e., the fallow period)
or increasing fertilizer and manure use efficiency through the justification of their
use. In addition, soil carbon losses, on annual croplands, can be reduced by
decreasing the frequency and intensity of soil tillage, in particular through con-
version to no-till practices (Paustian et al. 1997; Huggins et al. 1998).
In addition, Lal (2004) reported integrated pest management and drip irrigation
along with conservation tillage management as low carbon intensity practices. It
has been shown that carbon sequestration can dramatically influence the sustain-
ability of biofuels and particularly biogas (Korres et al. 2010); hence, cropping
system should be considered if precision, completeness, representativeness, and
comparability in LCA are to be secured (Korres 2013).
The statements above highlight the complexity of LCA technique in agricul-
tural systems but also in bioenergy production particularly when land use and land
use change are considered. It has been reported that indirect GHG emissions of
biofuels produced from productive land that could otherwise support food pro-
duction may be larger than the emissions from an equal amount of fossil fuels
(Delucchi 2006; Farrell et al. 2006). Kammen (2007) stated that attention to these