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from climate change (Bengtsson et al., 2005; Hole et al., 2005).
Enhanced biodiversity reduces pest outbreaks (Wyss et  al.,
1995; Pfiffner et al., 2003; Pfiffner and Luka, 2003; Zehnder
et al., 2007). Similarly, diversified agro-ecosystems reduce the
severity of plant and animal diseases while improving utilisa-
tion of soil nutrients and water (Altieri et al., 2005). Better soil
structure, friability, aeration and drainage, lower bulk density,
higher organic matter content, soil respiration (related to soil
microbial activity), more earthworms and a deeper topsoil layer
are all associated with the lower irrigation need (Proctor and
Cole, 2002). Under conditions in which water is limited during
the growing period, yields of organic farms are equal or signifi-
cantly higher than those of conventional agriculture common in
developing countries (Badgley et  al., 2007). Water capture in
organic plots was twice as high as in conventional plots during
torrential rains significantly reducing the risk of floods (Lotter
et al., 2003).
In Switzerland and the United States, organic matter, water
percolation through top layer and soil structure stability were
higher in organically managed soils than in conventional soils
(Mäder et  al., 2002; Marriott and Wander, 2006), making
organic fields less prone to soil erosion (Reganold et al., 1987;
Siegrist et al., 1998) and resulted significantly in higher yields
of corn and soya bean in dry years (Lotter et al., 2003; Pimentel
et al., 2005). In Tigray Province, one of the most degraded parts
of Ethiopia, agricultural productivity was doubled by soil fer-
tility techniques such as compost application and introduction
of leguminous plants into the crop sequence instead of using
purchased mineral fertilisers (Edwards, 2007). These reports
recommend the practice of organic farming to improve soil fer-
tility through green manuring, leguminous intercropping, com-
posting and recycling of livestock manure for reducing GHGs,
while also increasing global food productivity.
Eventually, a complete conversion to organic agriculture
could decrease global yields by 30-40% in intensively farmed
regions under the best geo-climate conditions (Niggli et  al.,
2009). In the context of subsistence agriculture and in regions
with periodic disruptions of water supply brought on by droughts
or floods, organic agriculture is competitive to conventional agri-
culture and often superior with respect to yields (Halberg et al.,
2006; Badgley et al., 2007; Sanders, 2007; Anonymous, 2008c).
Organic agriculture has a huge potential for climate change miti-
gation strategies in agricultural production (Pimentel et al., 1995;
Niggli et al., 2008, 2009):
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