The Economics of Desertification, Land Degradation, and Drought

Soil Nutrient Depletion
Soil nutrient depletion result from poor land management practice, which, in turn, leads to more
outflow of nutrients than inflow. Areas with naturally poor soil fertility, coupled with poor land
management, tend to suffer from severe soil nutrient depletion. For example, Natchergaele et al.
(2010) showed severe nutrient depletion in sub-Saharan Africa, where both soil fertility and land
management practices are generally poor. It is estimated that less than 3 percent of total cropland in
Sub-Saharan Africa is under sustainable land and water management practices (Pender 2009).
Recent studies have shown that integrated soil fertility management (ISFM), defined as the
judicious manipulation of nutrient stocks and flows from inorganic and organic sources for
sustainable agriculture production that fits the socioeconomic environment of farmers (Smaling et al.
1996), is more sustainable than fertilizer or organic soil fertility management practices alone
(Vanlauwe et al 2011). Examples of ISFM include practices which combine fertilizer with organic
inputs to restore soil nitrogen and organic matter. ISFM promotes judicious use of rock phosphate or
inorganic fertilizer to replenish phosphorus and other limiting nutrients. The ISFM approach has
become increasingly popular due to its win–win attribute of increasing both crop yield and carbon
stock. ISFM also reduces chemical fertilizer application rates and therefore has the potential to reduce
environmental pollution that arises from excessive application of fertilizers, which is now common in
southern Asia and South America (Phipps and Park 2002; Vanlauwe et al 2011). Some studies have
also shown that ISFM is more profitable than the use of fertilizer or organic matter alone. Twomlow,
Rusike, and Snapp (2001) found that marginal rates of return (MRR) from a mucuna–maize rotation
in Malawi were higher than from the use of inorganic fertilizer. Sauer and Tchale (2006) observed
similar results in Malawi. Mekuria and Waddington (2002) also found much higher returns from
ISFM than from fertilizer or manure alone.
However, other studies have shown ISFM to be less profitable than fertilizer or organic soil
fertility management practices alone. For example, in the Machakos district of Kenya, de Jager,
Onduru, and Walaga (2004) found a cost–benefit ratio of less than 1 in all trials involving organic and
inorganic soil fertility combinations, except one (combining inorganic fertilizer and manure in
irrigated maize production)—in the exception, the ratio was only 1.19.
Table 5.25.1 summarizes the type of land degradation and the solution to address each type.
As far as possible, the table also gives some examples of the impacts and profitability of the practices.
Table 5.1—Type of land degradation and their solutions
Type of land
degradation/processes
Solutions Examples of potential
impacts and profitability
Water-induced soil erosion • Mechanical methods: Soil and water
conservation structures; drainage structures
• Agronomic methods: Mulching; crop
management (cover crops, intercropping, and
so on); planting pattern/time
• Soil management methods: Minimum tillage or
no till; ridge tillage, tie tillage
Wind-induced soil erosion • Windbreak and dune stabilization using trees
and other vegetative methods
• Cover crops in humid or semihumid zones
• No till
• Rotational grazing and other practices that
improve land cover or prevent rotational
grazing
Salinity • Prevention of salinity
• Amelioration using intermittent or continuous
leaching
• Breeding for saline-resistant crop varieties
• Using halophyte crops, trees, and pasture
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• Standing crop residues
are 5–10 times more
effective in controlling
wind erosion than is
flattened crop residue
(von Donk 2004).