Production Practices and Quality Assessment of Food Crops. Vol. 1

Improvement of Grain Legume Production in Semi-Arid Kenya 169
even greater as the mean annual rainfall decreases. Characteristic of these areas is
the high intensity storms (over 40 mm day –1 ), which produce considerable runoff
in the absence of tree or bush cover. The rainfall regime is generally bimodal with
two peaks in November and April. The total annual rainfall ranges between 120–700
mm (Jaetzold, 1994), while potential evapotranspiration ranges between 1800–2500
mm. Evapotranspiration is a direct function of the prevailing temperatures and
altitude. Most of the ASALs are found at an altitude below 1500 m. Soils are generally
classified as sandy loams to loamy sands, and light to medium texture
inherently low in fertility and cation exchange capacity. These soils are prone to
compaction and capping. The native vegetation is mainly of the Acacia-thorn
savannah (semi-arid areas) and dwarf shrub (arid areas) type.
In the greater part of the arid areas, permanent rivers are lacking and only seasonal
rivers prevail. In these drier parts, underground water resources are more important
although quantities are generally very low. Water quality and quantity for both
human and livestock consumption is often insufficient. Drought, which is a recurrent
phenomenon in these arid areas, causes great livestock and crop losses resulting
in famine, destitution, poverty and heavy reliance on famine relief handouts. Because
of the natural climatic limitations in the ASALs, livestock rearing remains the single
most important source of subsistence for the inhabitants of the arid lands. Agropastoralism,
ranching and pure pastoralism are the main forms of land use. Crop
farming is, however, practised in the eco-climatic zone 5, or the so called ‘boundary
zone of rainfed agriculture’ (Shisanya, 1996; Jaetzold and Schmidt, 1983), although
there is normally a high risk of crop failure. Large tracts of land in the arid zone
are under National Parks and Game Reserves. The exploitation of these marginal
areas certainly requires a certain level of management skills to make them more
productive and sustainable – skills that the new settlers in these areas do not
possess (Quaye, 1994). The eventual mismanagement of such lands results in degradation
and a subsequent decrease in the productivity of the agricultural systems.
1.4. The need for agroecologically suitable ‘marginal’ food crops for the
1.2. sub-Saharan African drylands – the Kenyan example
Kenya’s ASALs have become the destination of unprecedented immigration, which
has led to land use conflict and resource degradation (Hornetz, 1997). In the last
three decades or so, there has been considerable human migration from the high
potential areas to the medium potential areas because of population pressure in
the former areas. The influx of population from the high potential areas to the
medium and low potential areas is likely to accelerate (Shisanya, 1999). Today, it
can be observed that settlers are moving into the wetter parts of the Ranching
zone, i.e. Lower – Lower Midland agroecological zone 6 (Shisanya, 1996). This
zone is only suitable for rainfed marginal cropping cultivation. According to the
government policy as outlined in the five-year Development Plan one third of the
projected increase in agricultural food production in Kenya was expected to come
from the new acreage largely in these marginal areas (Republic of Kenya, 1993).
Thus, it would seem that these areas will continued to play an important role with
regard to both human settlement as well as the production of subsistence food crops.