Chapter 1

 INTRODUCTION


 In light of the present food-production crisis facing most

countries of sub-Saharan Africa, numerous policy priorities have been

proposed by academics and politicians to encourage the rapid development

of technology to improve Africa's food production capacity (Swindale,

1980; USAID, 1985; Mellor et al., 1987; lyegha, 1988). High on many

priority lists is the need for scientific and technological research

directed towards the development of efficient fertilizer utilization

practices specifically adapted for the low-fertility soils common to

tropical regions.

 Shallow gravel horizons, frequently referred to as stone lines,

are common in soils throughout equatorial Africa. Stone-line soils are

generally considered to be agriculturally marginal; however, in a

continent where population growth is out pacing increases in

agricultural productivity, the development and utilization of marginal

lands for farming are increasing.

 Stones in the root zone of a soil reduce root penetration and

 water- and nutrient-holding capacities. These characteristics in turn

 reduce root exploitation of the soil mass and increase both the

 susceptibility of crops to water stress and the potential loss of

 nutrients by leaching.