Abstract
M.Ing. (Civil Engineering)
In South Africa water is considered to be a scarce resource, whichshould be used effectively.
By using scheduling, the Agricultural sector can help to alleviate the burden on this resource.
The determination of reference evapotranspiration (ETo) or potential evapotranspiration
(PET), form an integral part of any scheduling model. Four methods for the determination
of ETo was investigated, and their advantages and disadvantages singled
out. The combination method was found to be the best method, because it make use of a
mechanistic approach, and also take into account all the factors influencing evaporation.
The SWB program's Priestley-Taylor and the FAO combination methods for the
determination of PET was compared. Wheather data for Lions River, Pretoria, Rietrivier and
Stellenbosch was used in the comparison. The correlation between the methods was good,
especially after the initial difference was reduced, by multiplying the Priestley-Taylor method
with a constant.
The SWB program was used to simulate wheat growth. Data for the growth simulation of
cultivar SST86, was supplied by the Institute for Soil, Climate and Water. The comparison
between measured and simulated data are relatively good and could be further refmed. Data
for use in growth models are at present being accumulated for peanuts, tobacco and maize.