|dc.description.abstract||Irrigation in 1980 accounted for approximately 52 per cent of the water
consumed in Southern Africa. The need for planning water resources in
the agricultural sector is therefore apparent. Much of Southern
Africa's arable farming is carried out on land which, in terms of soil
moisture availability to crops, can be described as marginal. Information
on soil moisture is therefore valuable to the agriculturalist for
planning irrigation schemes and for dryland farming.
The objectives of this study were to provide the information mentioned
above. This was achieved by producing a detailed delimitation of 712
zones throughout Southern Africa, of more or less homogeneous climate
and by providing estimates of crop water requirements under dryland and
irrigated conditions in each zone. At the same time the bulk of information
which is normally forthcoming from such an analysis involving a
large number of combinations of possible input, i.e. crops, soils and
planting dates, was reduced, whilst the essential information content
was retained. The study provided inter alia an estimate of the
frequency of non-exceedance of certain levels of irrigation requirement,
based on analyses of soil moisture budgets using long daily rainfall
records. The soil moisture budgeting models which were used to estimate
the above information were verified inter alia using field measurements
of soil moisture.
The irrigation analysis was designed such that the results should not
became redundant when the inevitable improvement occurs in the estimation of crop factors or soil moisture variables nor if the farming practices
change with respect to planting dates.
A dryland soil moisture budget analysis for a range of crops and soils
was performed in addition to the abovementioned irrigation analysis.
The need for this latter study stemmed from the belief that irrigation
should not be considered in isolation but rather as one of a range of
options, many of them involving dryland farming, facing the agriculturalist.
In addition to the dissertation, this study produced a map of Southern
Africa on which the 712 homogeneous climate zones are depicted. For
each of these zones four pages of computer printout were produced.
These pages contain the results of the crop water requirements study for
irrigated conditions and the crop water requirement deficit, runoff and
an index of stress days for a range of crops, soils and planting dates,
under dryland conditions.||en