Agroecological Intensification of Smallholder Farming - The Oxford Topic of Food, Politics, and Society - page 111

The ecological principles of diversification complementarity, facilitation, and selec-
tion are relevant to agricultural diversification (Malezieux et al. 2009). Plant breed-
ing can enhance all three, in addition to directly affecting component productivity. To
enhance complementarity, plant breeders can design and select polyculture components
for distinct and noncompetitive niches. To enhance facilitation, breeders can select for
traits such as nitrogen fixation and chemical traits that provide benefits to other systems
components. In implementing participatory breeding strategies, formal-sector breeders
can provide surplus diversity to farmers, who then select the most adapted germplasm
for their local conditions (Ceccarelli et al. 2009).
Varietal performance of crops grown alone does not always predict performance in
an intercrop. In many intercropping studies, significant genotype-by-cropping system
interactions have been detected. This implies that varieties need to be evaluated in the
system in which they will be used (Gebeyehu et al. 2006). This is not, however, com-
monly appreciated or practiced by plant breeders. For example, although 97 percent of
teff fields were integrated with oilseed crops in a study in Ethiopia (Geleta et al. 2002),
teff breeders do not test the performance of teff varieties in combination with other
crops. In some cases, legumes have been bred for intercropping, for instance to avoid
shading their companion crops (e.g., cowpea; Singh et al. 1997).
Breeding for AEI performance could mean not only breeding for compatibility
with other crops in a system, but also better capacity for symbiotic relationships with
microbes that fix nitrogen (Mpepereki et al. 2000), help plants access phosphorus
(mycorrhizae), or protect them from pathogens (endophytes or epiphytes). More con-
ventional traits that can be considered part of AEI breeding would include breeding for
nutrient use efficiency and pest and disease resistance. These are broad fields that are
largely outside the scope of this chapter. From a nutritional perspective, AEI breeding
would entail selection for multiple production traits: leaf and grain, food and forage,
grain and green manure quality (human, animal, and soil nutrition are among the eco-
system services to be considered). Increasing nutrient content and availability (“biofor-
tification”) is another active field of research.
Managing Pests and Diseases
Pests are major sources of systems inefficiencies in agriculture. Oerke (2005) estimated
that ∼40 percent of crops are lost to insects, diseases, and weeds (collectively known as
pests) on a global basis. In East and West Africa, where little pesticide is used in most
smallholder production, losses were estimated at >50 percent. These losses would be
considerably higher if crop protection actions were not taken.
In the chemical boom-years that followed World War II, pesticides were considered
the answer to pest problems. Since then, a number of problems have emerged, includ-
ing health problems, environmental damage, and boom-and-bust cycles (Devine &
Furlong 2007; Williamson et al. 2008). In spite of the well-known downsides of pesticide
use, however, this remains the dominant method for pest management in agriculture.