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Increasing intensity of crop cultivation
Subsistence systems
Poor farmers, labor out-migration
Shifting cultivation
Long fallow-short fallow
Cash cropping systems
Land value high, peri-urban
Annual cropping
2-3 crops
per year
Continuous
vegetables
Declining soil fertility and organic matter
Increasing erosion risk
Increasing inputs and income
Increased pollution risk
FIGURE 15.1
Impacts of the intensification of cropping.
often unavailable or unaffordable. In areas with access to produce markets, a shift
to cash cropping can make purchased inputs affordable. In the most intensive cash
cropping areas, two or even three crops are grown annually, but careful management
of fertilizer inputs becomes critical in order to reduce the risks of pollution of surface
water and groundwater, especially in urban vegetable production systems. According
to Drechsel et al. (2008), the 20 million farmers in urban areas of West Africa could
productively use wastewater for irrigation or recycle nutrients in animal manures
provided that mechanisms for reducing health risks are put in place.
The highest rates of depletion of soil fertility occur when subsistence farmers,
who cannot afford inputs, increase cropping intensity to one or more crops per
year. McCown and Jones (1992) summarized the problem and depicted it as a spiral
poverty trap (Figure 15.2). The main drivers are population growth and low use of
e poverty trap
Low
population
Long
fallow
Soil
fertility
decline
High
population
Short or no
fallow
Low
yield
Low
income
Low
inputs
FIGURE 15.2
Poverty trap. (Adapted from McCown, R.L., and R.K. Jones, Agriculture of
semi-arid eastern Kenya: Problems and possibilities, In
A Search for Strategies for Sustainable
Dryland Cropping in Semi-arid Eastern Kenya
, ed. M.E. Probert, 8-14, Proceedings No. 41,
Canberra, Australian Centre for International Agricultural Research, 1992.)
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