Agriculture Reference
In-Depth Information
become salinized, groundwater overexploited and depleted, and freshwater fisheries
damaged. In addition, pollution may increase, lakes may shrink, ecosystems may
become degraded, biodiversity may be reduced, and habitats may be threatened.
Competition and conflict over water also becomes more likely—between nations in
a river basin, between pastoralists and farmers, between rural and urban areas, and
in general, between upstream and downstream populations (Harrington et al. 2006).
Further analysis of water issues is provided in Chapters 18 and 19.
lAnd degRAdAtIon
Land degradation in its many forms is another threat to sustainable food produc-
tion.
Land degradation
is understood to mean a loss in intrinsic quality that leads
to a decline in the capacity of land to satisfy particular uses (Blaikie and Brookfield
1987). Serious degradation can result in land losing its capacity to satisfy a wide
range of productive uses.
Land degradation and rehabilitation are influenced by natural forces as well as
by humans.
Net degradation
is the difference between naturally degrading pro-
cesses plus human-induced degradation on the one hand and natural reproduction
plus restorative management on the other. Land degradation is understood to include
wind and water erosion; loss of organic matter and soil nutrients; soil salinization,
acidification, compaction, and crusting; and reduced biological activity in soils.
At the global level, land availability appears adequate to meet future growth in
demand for food. Around 11% of the world's land surface is thought to be generally
suitable for food and fiber production, while another 24% is used for grazing and
31% for forests (Eswaran et al. 1999). Land degradation, however, whittles away
at these totals, effectively reducing the quantity and quality of land available for
agricultural uses. Unfortunately, there are few good estimates of the global extent
of land degradation and its effect on productivity (World Bank 2007). Some ana-
lysts continue to rely on the GLASOD (Global Assessment of Human Induced Soil
Degradation) study, which estimated that at the global level, forest areas, grazing
areas, and agricultural areas are 18, 21, and 38% degraded, respectively (Oldeman
1992). These estimates, based on consensus judgment, are somewhat contentious and
in any event say little about the effect of degradation on productivity.
Land degradation is considered a threat to sustainable food production because
it reduces present and undermines future productivity. In point of fact, however,
the effect of land degradation on productivity is notoriously difficult to measure.
Farmers may mask the effects of degradation by adjusting land use or applying extra
inputs. In addition, there may be “threshold effects.” Deep, highly fertile soils may
undergo erosion for extended periods of time with little loss in productivity—until
at some point they become so thin that rapid yield losses begin to unfold (Scherr and
Yadav 1996).
Land degradation has an additional dimension: Its effects are often felt beyond
the field or farm where it occurs. Erosion on hillsides on upper catchments can result
in siltation of downstream irrigation infrastructure, degradation of water quality for
downstream urban consumers, and reduced productivity of downstream fisheries.
