Agriculture Reference
In-Depth Information
projections of irrigation in sub-Saharan Africa are low and need to be aggressively
explored and expanded. Future expansion of irrigation in sub-Saharan Africa can
be achieved by developing small-scale projects rather than grandiose or large-scale
irrigation schemes.
The most prevalent method of applying water to soils in Asia, Africa, and else-
where is though flood irrigation. This is the most traditional method and is rather
wasteful because of high losses in conveyance, evaporation, and seepage. With
increase in water scarcity and competition from industry and urbanization (Johnson
et al. 2001; Kondratyev et al. 2003; Gleick 2003), there is a strong need to improve
water use efficiency. Among RMPs for improving water use efficiency, from the cur-
rent range of merely 5 to 30%, are subirrigation and drip irrigation combined with
fertigation. Losses by evaporation can be decreased through mulch farming tech-
niques. Use of plastic mulch, while suppressing weed growth, can drastically reduce
evaporation. Plastic mulch is widely used in East Asia (e.g., China, Korea, Japan) but
rarely in South Asia and sub-Saharan Africa.
bIofuel
There is a strong, and rightfully justified, enthusiasm to use biofuel for power genera-
tion and transport (Brown 1998; EPA 2005; Weisz 2004; Pacala and Socolow, 2004).
It is in this connection that the use of crop residues for producing lingocellulosic etha-
nol is widely being considered (Somerville 2006). It is important, however, to realize
that traditional biofuels (crop residues and dung for cooking) are widely used in Africa
and Asia and have severe adverse environmental, health, and agronomic implications.
Venkatraman et al. (2005) reported severe adverse climatic impacts at the regional level
because of the smoke and soot generated by traditional biofuels.
Crop residue, animal dung, and other biosolids (municipal waste, sludge) must
be used as soil amendments rather than for short-term economic gains as traditional
or modern biofuels (Wilhelm et al. 2004). Therefore, lignocellulosic materials for
bioethanol must be grown by establishing energy plantations. Such plantations must
be established on specifically identified land so that plantations do not compete with
cropland and by specifically chosen and dedicated species so that crop residues can
be returned to soil as amendment. There is a wide range of species that can be used
for establishing energy plantations. These include short-rotation woody perennials
(e.g., poplar, willow, mesquite, eucalyptus, leucaena, gliricidia, acacia); grasses (e.g.,
switch grass, elephant grass, guinea grass, napier grass, karnal grass); algae; and
halophytes, which can be grown by irrigation with brackish water. Even the low-
input and high-density prairie grasses can be used for producing biofuels (Tilman
et al. 2006).
Soils of sub-Saharan Africa and South Asia are degraded and nonresponsive to
input because their SOC/SOM pools have been severely depleted and are below the
critical levels needed to maintain processes essential for plant growth and ecosystem
services. Continuous removal of crop residues, for traditional or modern biofuels and
other competing uses, can exacerbate soil and environmental degradation. These
trends must be reversed for the urgency to break the agrarian stagnation and meet
