Agriculture Reference
In-Depth Information
among a suite of sustainable agricultural practices that can rebuild soil fertility and
SOM, and break the cycle of poverty (Lal 2004).
11.1.2 d
efinition
And
o
bjectiveS
Agroforestry is broadly defined as a set of land use practices that deliberately com-
bine trees, shrubs, palms, or bamboo with agricultural crops or animals (Sileshi et
al. 2007). This chapter will describe how agroforestry practices increase soil fertility
and cereal yields for small landholders, as well as increase biomass and soil C accu-
mulation. Emerging data on the increase in GHG emissions with agroforestry will
also be presented, which will inform discussions of the trade-offs between small-
holder households and the ecosystem-wide benefits of agroforesty.
The benefits of agroforestry are often classified as ecosystem services, which are
conditions and processes through which ecosystems sustain human life (Tallis and
Kareiva 2005). Ecosystem services may be divided into four categories: provision-
ing, regulating, supporting, and cultural services (Sileshi et al. 2007; Carpenter et al.
2009). Provisioning services of agroforestry/crop combinations include provision
of food from increased soil fertility and improved soil water balance, and timber
and fuelwood from rotational woodlots. Regulating services include erosion con-
trol, improved water infiltration, and C sequestration. Supporting services include
biomass production and soil fertility improvement. Finally, cultural services include
spiritual, cognitive, and aesthetic services.
11.1.3 b
enefitS
And
c
onStrAintS
of
A
groforeStry
For smallholder farmers, the major benefit from using the soil-fertility-enhancing
agroforestry practices described above is the increased yield that can lead to greater
food security or additional income. At the same time, few farmers are aware of the
possibility of receiving additional payments for the C sequestration service provided
by the systems. Only a very small number are actually benefiting from soil C pay-
ments (the first ever scheme in western Kenya is very new), and the price paid for
sequestered C is very low. Thus, the fact that agroforestry practices can sequester C
through tree biomass and soil C buildup is not an important factor in farmers'
ex ante
or
ex post
evaluations of the practices.
What motivates farmers to adopt and manage agroforestry practices for soil fertil-
ity depends on the context, which includes how distinct these practices are from tradi-
tional farming practices. There are some locations where farmers have long practiced
the integration of naturally regenerated trees in their crop fields. The main example
of this is the parkland system in the West African Sahel (Boffa 1999); however, estab-
lishment of similar systems is possible in many dryland areas throughout Africa.
Almost all drylands are important areas for tree regeneration. In typical parkland
systems, trees regenerate naturally from roots or seed, and farmers retain those trees
that are beneficial to them. From an economic point of view, the integration of trees
for yield improvement in these types of systems is attractive for the following reasons:
dryland areas have lower labor-to-land ratios than humid and subhumid areas, and
thus labor-saving practices such as tree regeneration and management are compatible
