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Oktober 2017
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Variable rate irrigation technology
– determine the economic benefit
E
ver increasing production costs are a serious threat to the
sustainability of irrigation producers. Over the past 15 years,
production costs of wheat and maize under irrigation in-
creased significantly. The major contributors towards the
increase in production costs are fertiliser, seed and irrigation costs.
Increases in irrigation costs are due to ever increasing electricity
costs. The recent increases in electricity tariffs have created seri-
ous problems for irrigation producers. Thus, irrigation producers will
need to evaluate different options to manage electricity and water
costs in the future.
Significant opportunities exist for irrigation producers to reduce
electricity costs through irrigation system design, renewable ener-
gy resources and operating practices to improve profitability.
Renewable energy resources (wind energy, hydroelectricity and
solar panels) require a large amount of capital and are not always
affordable to irrigation producers with a cash flow constraint. The
design of an irrigation system and the operating practices need to be
evaluated in order to reduce electricity costs.
Potential electricity savings can be achieved by adopting new tech-
nologies such as variable speed drives, high efficiency motors and
variable rate irrigation. Variable rate irrigation allows the irrigator to
apply different volumes of water to each section of the field which
maximise yields and profitability (Lindsay, undated).
Variable rate irrigation has a few potential benefits for the irrigator,
which include the following (Lindsay, undated):
Savings in electricity costs
Easy to use – saves time
Efficient watering
Customised to specific field needs
Different application rates for different soils or crops save
water, energy and fertiliser/chemicals
Reduces overwatering on laterals and part circle pivots
Saves water as individual sprinklers or zones can be turned
off over tracks, drains, creeks and bridges
Decreases and eliminates watering in low or flooded areas
Reduces leaching and runoffs on tighter soil areas
Less track maintenance
However, despite all the potential benefits, it is important to com-
pare the investment costs of variable rate irrigation with the potential
electricity cost savings, thus, taking cognisance of the trade-off be-
tween investment costs and electricity costs.
When variable rate irrigation is applied to an irrigation system the
flow rate and pressure requirement of the system change, since dif-
ferent volumes of water are applied to each section of the field. The
change in flow rate and pressure requirement change the kilowatt
usage and irrigation hours of the system, which change the electric-
ity costs and can lead to electricity cost savings.
FOCUS
Irrigation
Special
MARCILL VENTER,
Department Agricultural Economics, University of the Free State
PERCENTAGE
OPERATING
TIME (%)
FLOW RATE
(M
3
/H)
PRESSURE
REQUIRE-
MENT (M)
KILOWATT
(KW)
PUMPING
HOURS
(HOURS)
VARIABLE
ELECTRICITY
COSTS (R)
FIXED
ELECTRICITY
COSTS (R)
TOTAL
ELECTRICITY
COSTS (R)
30%
100,5
21,1
16,2
827
7 827
4 211
12 038
50%
125,5
22,4
21,8
1 118
13 900
7 019
20 919
10%
150,5
24,1
24,9
186
2 639
1 404
4 043
10%
178
22,9
29,6
160
2 688
1 404
4 092
Total
27 054
14 038
41 092
TABLE 1: PARAMETERS AND ELECTRICITY COSTS FOR USING VARIABLE RATE IRRIGATION TECHNOLOGY
FOR HIGHER OPERATING TIMES AT LOWER FLOW RATES USING RURAFLEX.
TABLE 2: PARAMETERS AND ELECTRICITY COSTS FOR USING VARIABLE RATE IRRIGATION TECHNOLOGY
FOR HIGHER OPERATING TIMES AT HIGHER FLOW RATES USING RURAFLEX.
PERCENTAGE
OPERATING
TIME (%)
FLOW RATE
(M
3
/H)
PRESSURE
REQUIRE-
MENT (M)
KILOWATT
(KW)
PUMPING
HOURS
(HOURS)
VARIABLE
ELECTRICITY
COSTS (R)
FIXED
ELECTRICITY
COSTS (R)
TOTAL
ELECTRICITY
COSTS (R)
10%
100,5
21,1
16,2
276
2 609
1 404
4 013
10%
125,5
22,4
21,8
224
2 780
1 404
4 184
50%
150,5
24,1
24,9
932
13 196
7 019
20 215
30%
178
22,9
29,6
479
8 064
4 211
12 275
Total
26 648
14 038
40 686