Geoscience Reference
In-Depth Information
pollutants (Elbakidze and McCarl, 2007). In producing bioen-
ergy, feedstock can either be crop residue or a densely rooted
perennial crop which either will reduce soil quality by depleting
soil organic matter or may improve soil quality by replenish-
ing organic matter, respectively (Paustian et al., 2004). A key
potential trade-off is between the production of bioenergy crops
and food security. Food insecurity is determined more by ineq-
uity of access to food than by absolute food production insuf-
ficiencies, so the impact of this trade-off depends, among other
things, on the economic distributional effects of bioenergy pro-
duction (Smith et al., 2007a). Efficiently managed bioenergy
plantations cannot only reduce nutrient leaching and soil ero-
sion but also increase nutrient recirculation, stock soil carbon,
improve soil fertility, remove cadmium or other heavy metals
from soils or wastes, aid in the treatment of nutrient-rich waste-
water and sludge and provide habitats for biodiversity in the
agricultural landscape (Berndes and Börjesson, 2002; Berndes
et al
.,
2004; Börjesson and Berndes, 2006).
The practices maintaining/increasing crop productivity can
also ensure food security during the coming decades (Anonymous,
2003, 2005a; Rosegrant and Cline, 2003; Lal, 2004a,b; Follett
et al., 2005; Sanchez and Swaminathan, 2005). Carbon conserv-
ing practices also sustain or enhance fertility, productivity and
resilience of soil resources (Díaz-Zorita et al., 2002; Cerri et al.,
2004; Freibauer et al., 2004; Kurkalova et al., 2004; Lal, 2004a;
Paustian et al., 2004). Agro-ecosystems are primarily dependent
on manufactured fertilisers (Galloway et al., 2003; Galloway,
2003). The practices that improve nitrogen-use efficiency reduces
N
2
O emission, thus it also reduces GHG emissions from fertiliser
manufacture and avoids deleterious effects on water and air qual-
ity from N pollutants (Dalal et al., 2003; Paustian et al., 2004;
Oenema et al., 2005; Olesen et al., 2006). However, where pro-
ductivity is improved by increasing inputs, soil acidification or
salinisation may occur (Barak et al., 1997; Connor, 2004; Díez
et al., 2004). Fresh water is becoming scarce and agricultural
practices for mitigation of GHGs can either have negative or posi-
tive effects on fresh water conservation and quality (Rockström,
2003; Rosegrant and Cline, 2003). Some practices could inten-
sify water use by reducing stream flow or groundwater reserves
(Unkovich, 2003; Dias de Oliveira et al., 2005) while some may
affect water quality through enhanced leaching of pesticides
and nutrients (Machado and Silva, 2001; Freibauer et al., 2004).
Highly productive, evergreen, deep-rooted bioenergy plantations
generally have a higher water use than the land cover they replace
(Berndes, 2002; Jackson et al., 2005).
