10
hydrological cycle and its partitioning into different components are determined by
the climatic parameters at micro-, meso-, and macroscales. Retention, denaturing,
filtration, and purification are done during percolation of water through the soil
solum. Land use and management is a strong control of the hydrological cycle and
its partitioning into different components.
The low agronomic yield and perpetual hunger have persisted in SSA despite the
widespread adoption of improved varieties developed by the national and international programs including those released by the CGIAR centers (e.g., CIMMYT,
ICRISAT, ICARDA, IITA, WARDA, IRRI, ILCA, ICRAF). Indeed, the Green
Revolution (GR) of the 1960s by-passed SSA despite the availability of improved
varieties because other components (i.e., fertilizers, irrigation, appropriate farm
machinery, and energy-based inputs) were either not available to the resource-poor
farmers and small landholders (<5 Ha) or farmers were not sure of their usefulness
because of the fragile soils and harsh environments.
Soils of SSA are prone to a range of soil degradation processes – physical, chemical, biological, and ecological. The extent and severity of degradation (especially
the physical degradation by accelerated erosion) will exacerbate due to the evergrowing pressure of the rapidly increasing population in conjunction with the
increase in frequency and intensity of extreme events (e.g., drought stress, heat
wave, high incidence of pests and pathogens including infestation by weeds).
Further, the extent and severity of soil degradation is related to the interaction
between the factors and causes of soil degradation. Among the causes, the human
dimensions are the critical determinants of soil degradation. Indeed, the biophysical
process of soil degradation is strongly influenced by the socio-economic, political,
and cultural factors including the land tenure and the gender-related issues (Lal
2007a). A high percentage of farms in SSA are operated by women, and often the
technological advances are neither available because of being prohibitively expensive nor are these often appropriate for their specific needs.
Rather than the seed-centric approach of the conventional GR package of the
1960s, the constraints to narrowing the yield gaps must be addressed through a soilcentric approach (Lal 2019). The latter must be based on restoration and sustainable
management of soil health (physical, chemical, biological, and ecological). In this
context, key determinants of soil health must be identified and judiciously managed
(Lal 2016c). As is evident, the yield potential of elite varieties can only be realized,
if grown under optimal conditions of soil environments especially those of soil
physical conditions (e.g., structure, tilth, plant available water capacity, and water
infiltration rate and soil temperature regime).
Most soils of agroecosystems of SSA are severely depleted of their soil organic
carbon (SOC) concentration and stock. The SOC concentration in the root zone of
upland soils may be as low as 1 g/kg or lower in comparison with the threshold level
of >11 g/kg (Aune and Lal 1997) and preferably 20 g/kg (Loveland and Webb
2003). Severe depletion of the SOC concentration may be attributed to a widespread
adoption of extractive farming practices such as residue removal for competing uses
(e.g., feed, fuel, fencing and house construction, and uncontrolled grazing), in-field
burning, and none or low rate of inputs of organic and inorganic amendments.
B. R. Singh et al.
hydrological cycle and its partitioning into different components are determined by
the climatic parameters at micro-, meso-, and macroscales. Retention, denaturing,
filtration, and purification are done during percolation of water through the soil
solum. Land use and management is a strong control of the hydrological cycle and
its partitioning into different components.
The low agronomic yield and perpetual hunger have persisted in SSA despite the
widespread adoption of improved varieties developed by the national and international programs including those released by the CGIAR centers (e.g., CIMMYT,
ICRISAT, ICARDA, IITA, WARDA, IRRI, ILCA, ICRAF). Indeed, the Green
Revolution (GR) of the 1960s by-passed SSA despite the availability of improved
varieties because other components (i.e., fertilizers, irrigation, appropriate farm
machinery, and energy-based inputs) were either not available to the resource-poor
farmers and small landholders (<5 Ha) or farmers were not sure of their usefulness
because of the fragile soils and harsh environments.
Soils of SSA are prone to a range of soil degradation processes – physical, chemical, biological, and ecological. The extent and severity of degradation (especially
the physical degradation by accelerated erosion) will exacerbate due to the evergrowing pressure of the rapidly increasing population in conjunction with the
increase in frequency and intensity of extreme events (e.g., drought stress, heat
wave, high incidence of pests and pathogens including infestation by weeds).
Further, the extent and severity of soil degradation is related to the interaction
between the factors and causes of soil degradation. Among the causes, the human
dimensions are the critical determinants of soil degradation. Indeed, the biophysical
process of soil degradation is strongly influenced by the socio-economic, political,
and cultural factors including the land tenure and the gender-related issues (Lal
2007a). A high percentage of farms in SSA are operated by women, and often the
technological advances are neither available because of being prohibitively expensive nor are these often appropriate for their specific needs.
Rather than the seed-centric approach of the conventional GR package of the
1960s, the constraints to narrowing the yield gaps must be addressed through a soilcentric approach (Lal 2019). The latter must be based on restoration and sustainable
management of soil health (physical, chemical, biological, and ecological). In this
context, key determinants of soil health must be identified and judiciously managed
(Lal 2016c). As is evident, the yield potential of elite varieties can only be realized,
if grown under optimal conditions of soil environments especially those of soil
physical conditions (e.g., structure, tilth, plant available water capacity, and water
infiltration rate and soil temperature regime).
Most soils of agroecosystems of SSA are severely depleted of their soil organic
carbon (SOC) concentration and stock. The SOC concentration in the root zone of
upland soils may be as low as 1 g/kg or lower in comparison with the threshold level
of >11 g/kg (Aune and Lal 1997) and preferably 20 g/kg (Loveland and Webb
2003). Severe depletion of the SOC concentration may be attributed to a widespread
adoption of extractive farming practices such as residue removal for competing uses
(e.g., feed, fuel, fencing and house construction, and uncontrolled grazing), in-field
burning, and none or low rate of inputs of organic and inorganic amendments.
B. R. Singh et al.