Further results show monthly and
total irrigation water required for
different levels of nonexceedance, as well as levels of
efficiency of irrigation water use
and rainfall use efficiency.
Another set of results show irrigation requirements on a year-onyear basis in millimetre (see figure
5) as well as cubic meters for the
area planted. Daily water balances can be inspected, specifically
for identifying water stress situations.
Figure 5: Crop irrigation requirements expressed in mm
SAPWAT3 is used by all irrigation
designers in South Africa to optimise water use to its fullest extent.
A variety of answers is possible depending on an irrigation strategy
selected. One such case is short
grower maize planted on 15 December. If the irrigation strategy is
to make best possible use of rainfall
by not filling the soil profile to field
capacity during irrigation, irrigation
water required is 320 mm. If the
irrigation strategy is changed to
always fill the soil profile to field
capacity, which results in low rainfall use e ff