Agriculture Reference
In-Depth Information
1.8 ADAPTATION TO CLIMATE CHANGE
Crop yields on small landholder farms are vulnerable to climate change and the attendant
soil degradation. Small landholders have a limited capacity to adapt. Thus, crop produc-
tion may decline in the tropics even with a moderate increase in temperature (Long et al.
2005). Furthermore, the fertilization effect of CO
2
may be less than projected because
of the increasing risks of drought and deficiency of some essential nutrients. Lack of
access to irrigation water or the means to use water effectively and efficiently are the key
factors (Postel et al. 2001). Furthermore, nations with large natural resources will fare
better in adapting to climate change than those in developing countries (Easterling and
Apps 2005) where the majority of the resource-poor small landholders are located. For
example, small farmers in the high Andes (e.g., Bolivia, Ecuador, and Peru) are prone
to climate change and the potential decline in productivity (Fonte et al. 2012). Similarly,
farmers in Sahel and South Asia are vulnerable to climate change and uncertainties. In
northern Ghana, farmers are diversifying farming to adapt to variable and uncertain
climate (Laube et al. 2012). Adaptation measures include use of shallow groundwater
irrigation of vegetables for urban market. Adaptation to climate change must be linked
to achieving food security in developing countries. For example, transformation of low-
productivity croplands to sequential agroforestry can triple system C stocks in 20 years
(Sanchez 2000) and offset anthropogenic emissions.
1.9 MANAGEMENT OF SOIL ORGANIC MATTER
SOM is the elixir of all terrestrial life. Yet, soils managed by small landholders
are severely depleted of their SOC pool because of the use of extractive farming
practices for a long time. Thus, SOC concentration must be restored to above the
threshold level of ~1.5% in the rootzone. Indeed, SOC concentration and stock are
important determinants of soil quality (Craswell and Lefroy 2001; Palm et al. 2001).
Therefore, one of the biggest challenges in warm tropical climates is identification
and use of technologies to restore SOM concentration in small landholder farms.
Appropriate SOM-enhancing technologies, for small landholders in SSA and else-
where, must be based on three characteristics (Snapp et al. 1998): (i) residue quality,
(ii) importance of deep-rooted species, and (iii) trade-offs between legumes grown
for food vs. those established for improving soil quality. In general, species that
combine some grain yield with high above- and below-ground biomass (i.e., low N
harvest) are useful for the dual goal of achieving food security and improving soil
fertility and SOC concentration (Snapp et al. 1998).
In some cases, crop yields can be strongly correlated with SOC concentration in
the root zone (Zingore et al. 2008). However, SOC cannot always be used as an index
of N supply under all conditions, and the correlation between SOC and N supply may
be poor (Cassman et al. 1996). Thus, better understanding of processes governing N
dynamic in soils of the tropics is needed toward the development of sustainable crop
management practices. Indeed, nutrient input use is the main factor limiting produc-
tivity of cereals in SSA (Cobo et al. 2009). In addition to plant nutrients, soil quality
indicators must be broad based and include variables such as SOC saturation deficit,
compaction, surface scale up, and other biological attributes (Sanchez et al. 2003).
