Global Extent of Land Degradation and Its Human Dimension - Principles of Sustainable Soil Management in Agroecosystems - page 219

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40 29

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0

North
America

Southern
Asia

LAC Europe Oceania Central

Asia

SSA

FIGURE 9.6 Average fertilizer nutrient application rate, 2005-2009. (Courtesy of
FAOSTAT.)

Soil nutrient depletion is a major form of land degradation and is perceived to be
the main driver of low agricultural productivity in SSA (Van Reuler and Prins 1993;
Sanchez et al. 1997). SSA applies to only about 10 kg/ha of elemental NPK, a level
that is the lowest in the world and lower than 10% of the rate applied in southern
Asia (Figure 9.6). As a result of this, soil nutrient depletion is severe. Estimates show
that the annual value of depleted nutrients in SSA is about $4.5 billion (Gregersen et
al. 2007), which is about 0.5% of the region's US$895 billion GDP in the same year
(IMF 2012). The low adoption of chemical fertilizer in SSA is largely due to its high
cost, which is precipitated by poor transportation infrastructure in the region.
Depletion of soil organic matter can also lead to significant yield reduction.
Studies have shown that increasing soil carbon in the root zone by 1 ton ha −1 could
increase yields by 20-70 kg ha −1 for wheat, 10-50 kg ha −1 for rice, and 30-300 kg ha −1
for maize (Lal 2006). It is estimated that increasing the global soil carbon pool in the
root zone could increase cereal production by 32 million tons per year (Lal 2006),
a level that is about 3% of the 1 billion ton cereal production in food-deficit poor
countries (FAOSTAT 2009). Organic inputs could also improve soil ecology, as well
as a score of other ecosystem services (Powlson et al. 2011).
Below, we demonstrate the impact of soil fertility management on maize and
rice yields using Mali and Nigeria as case studies. The analysis is based on only soil
nutrient and soil carbon depletion. We also examine the profitability of ISFM and
land degrading practices, as well as their adoption rates in the countries included in
the case study.

9.5.2 I mpact of L and d egradatIon on m aIze and r Ice
y IeLd : t he c aSe of m aLI and n IgerIa
Table 9.4 shows that the 30-year average yield of ISFM practice is more than twice
the corresponding yield for the land degrading management practice for both maize