Agroecological Intensification of Smallholder Farming - The Oxford Topic of Food, Politics, and Society - page 108

These examples illustrate the need to supply nutrients for many smallholder farming
contexts, and they underline the point that maintaining healthy and productive soils
involves more than supplying inorganic fertilizer. Soil organic matter must be main-
tained in order to support the efficient use of applied nutrients, as well as to hold water.
Legumes can fix nitrogen and increase P availability, but only if their symbiotic relation-
ships with microorganisms, as well as their pests and diseases, are effectively managed.
In well-endowed farming contexts, organic agriculture often entails the massive import
of nutrients into the system, typically in the form of high-quality manure, an asset not
available to most resource-limited smallholder farmers. These issues are considered in
greater detail below.
Examples and Evidence from
AEI Frontiers
Managing Systems Diversity
Diversity has several potential functions within agroecosystems, including reducing risk
(van Noordwijk et al. 1994), increasing productivity, and allowing for improved diets.
In the context of well-endowed systems, these functions can be accomplished through
the use of inputs and markets. Industrialized agricultural systems have favored mono-
cultures, partly because these are easier to manage in mechanized systems, and partly
because market efficiencies encourage specialization. Although the majority of calories
produced through agriculture now come from just a few species, there is tremendous
potential to diversify systems with the vast number of species and within-species diver-
sity available. Crop and livestock diversity can be directly manipulated, with varying
effects on systems productivity and stability. The diversity of farming systems includes
the species intended by the farmer, as well as the associated diversity (life forms other
than those planned by the farmer). Associated diversity can contribute to positive func-
tions such as pollination and decomposition, or it can be harmful, as discussed in the
section on pests below. The extent of associated diversity tends to correlate with the
diversity that farmers implement (Vandermeer et al. 1998). Diversity can be handled in a
range of ways, both temporally (simultaneous planting, overlapping life cycles, in series)
and spatially (patch size, arrangements, segregation and integration at different scales).
Options include intraspecific mixtures and multilines, intercrops, relay cropping (one
crop goes in while the other is maturing), rotations, agroforestry and crop-livestock
integration. A recent review summarized the various benefits and drawbacks of annual
intercrops (Lithourgidis et al. 2011).
In studies of crop mixtures and intercrops, the more diverse systems typically outper-
form the corresponding monoculture systems. A range of mechanisms can contribute
to the superior performance of polycultures. One mechanism is reduced competition,