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Freddie R.
Lamm, Research Irrigation Engineer
flamm@ksu.edu
Loyd R.
Stone, Research and Teaching Soil Scientist
lrstone@ksu.edu
Danny H.
Rogers, Extension Irrigation Engineer
drogers@falcon.bae.ksu.edu
The profitability of converting from furrow surface irrigation to a center pivot sprinkler irrigation system depends upon a number of factors. These include a) the pumping capacity of the irrigation well, b) the cost of converting to the sprinkler irrigation system and loan repayment period, c) changes (if any) in irrigated acreage, and d) comparative irrigated crop yields for the old and new systems. Labor savings are also commonly thought to be a major consideration in switching from furrow surface irrigation to center pivot irrigation systems. Other factors considered include long run crop prices, production costs, and taxrelated depreciation and interest deductions for the pivot system investment.
Center Pivot Sprinkler Investment Costs & Tax
Deductions
Current budget estimates from KSU Farm Management Guide MF836 (Irrigation
Capital Requirements and Energy Costs) as well as irrigation industry cost
projections are used to estimate the purchase cost of a sprinkler irrigation
system (Table 1). An additional
$4,500 is budgeted to modify the existing well pump for the higher pressure
requirements of sprinkler irrigation. The total cost of the pivot sprinkler
system is projected to be $45,209, including a standard 7 tower pivot system
with drops, low drift nozzles, underground pipe from the field edge to the
Table 1.
Capital Requirements for a Center Pivot irrigation System (125 acres).
Item 
Feet 
Price/ft 
Costs 
Standard 7 Tower Center Pivot 



System Base Price 
1,320 

$28,000 
Drops on 80” Spacing 


2,100 
Low Drift Nozzles 


2,400 
38” x 11.2 Tires 


3,000 
8”
Underground Pipe 
1,320 
$2.52 
3,326 
Electrical
Wiring 
1,320 
$1.90 
2,508 
Connectors 


1,500 
12
KVA Generator 


2,375 
Total
Cost of Center Pivot System 


$45,209 




Pump
Modification Cost 


$4,500 




Total
System & Pump Cost 


$49,709 
A key aspect of this analysis involves the comparison of irrigated corn yields
and net returns across a range of five different gross irrigation pumping
capacities for alternative irrigation systems (Table 2.). Irrigation schedules
(water budgets) are simulated for the 19721998 period using climatic data
from the KSU Northwest ResearchExtension Center in Colby, Kansas. Irrigation
is scheduled as needed according to the climatic conditions, but is limited to
the frequencies for the two systems as indicated in Table 2. The irrigation
season is limited to the 90 day period between June 5 and September 2. The
first furrow surface irrigation event in each year is on June 15, reflecting a
typical date of first irrigation following the final furrowing process. After
that, furrow irrigation events are scheduled as the capacity limitation allows
and if the calculated irrigation deficit exceeds 3 inches. Center pivot
sprinkler irrigation events are scheduled during the 90day period as the
capacity limitation allows and if the calculated irrigation deficit exceeds 1
inch.

Center Pivot

Furrow
Surface


Gross
Irrigation
Capacity
Inches per Day 
Frequency & Amount Applied 
Flowrate
Gpm per 125 acres 
Frequency & Amount Applied 
Flowrate
Gpm per 160 acres 
0.250” 
1” in 4 days 
589 
3” in 12 days 
754 
0.200” 
1” in 5 days 
471 
3” in 15 days 
603 
0.167” 
1” in 6 days 
393 
3” in 18 days 
503 
0.125” 
1” in 8 days 
295 
3” in 24 days 
377 
0.100” 
1” in 10 days 
236 
3” in 30 days 
302 
Irrigated
corn yields for the various alternative irrigation systems and irrigation
capacities are also simulated for the same 27 year period using the evapotranspiration
(ET) estimates from the irrigation schedules and using a yield production
function developed by Stone et al. (1995). In its simplest form, the model
results in the following equation,
with
yield expressed in bushels/ acre and ET in inches. Further application of the
model reflects weighting factors for specific growth periods. These additional
weighting factors are incorporated into the simulation to better estimate the
effects of irrigation timing for the various systems and capacities. The
weighting factors and their application to the model are discussed in detail
by Stone et al. (1995).
In these profitability projections, the long term corn selling price is
assumed to be $2.36 per bushel in western Kansas. USDA Production Flexibility
Contract payments on irrigated corn acres are assumed to be $35/ acre. The
long term wheat selling price is assumed to be $3.18 per bushel with wheat
yields assumed to average 44 bushels per acre. Dryland notill corn yields are
assumed to average 82 bushels per acre. Farm program Production Flexibility
Contract (PFC) payments on dryland wheat and corn acres are assumed to be $10
per acre. The fuel, oil and maintenance cost of applying irrigation water
through a center pivot is assumed to be $3.02 per acreinch, and $2.62 per
acreinch for surface irrigation systems.
Long Term Average Irrigation
Requirements and Corn Yields
The simulated irrigation schedules an
d corn yield model are use
Table 3.
Average Irrigated Corn Yields and Irrigation Application Amounts for
19721998^{a.}

0.25”/day 
0.20”/day 
0.167”/day 
0.125”/day 
0.10”/day 
Full Irrigation 


Irr. Amount (in) 
Corn Yield (bu/a 
Irr. Amount (in) 
Corn Yield (bu/a 
Irr. Amount (in) 
Corn Yield (bu/a 
Irr. Amount (in) 
Corn Yield (bu/a 
Irr. Amount (in) 
Corn Yield (bu/a 
Irr. Amount (in) 
Corn Yield (bu/a 
A. Center
Pivot Sprinkler System @ 100% Application Efficiency on 125 acres
(CP100%)


Frequency 
1” in 4 days 
1” in 5 days 
1” in 6 days 
1” in 8 days 
1” in 10 days 
Full Irrigation 

GPM Rate 
589 gpm 
471 gpm 
393 gpm 
295 gpm 
236 gpm 


Average 
13.3 
196 
12.0 
188 
10.7 
177 
8.6 
156 
7.2 
140 
13.9 
197 
Std
Deviation 
3.9 
43 
3.1 
36 
2.4 
4.2 
1.7 
24 
1.2 
25 
4.2 
44 
Minimum 
5 
111 
5 
111 
5 
5 
4 
103 
4 
92 
5 
111 
Maximum 
20 
261 
17 
254 
14 
21 
11 
188 
9 
174 
21 
269 
B. Center
Pivot Sprinkler System @ 85% Application Efficiency on 125 acres
(CP85%)


Frequency 
1” in 4 days 
1” in 5 days 
1” in 6 days 
1” in 8 days 
1” in 10 days 
Full Irrigation 

GPM Rate 
589 gpm 
471 gpm 
393 gpm 
295 gpm 
236 gpm 


Average 
14.6 
192 
12.9 
179 
11.4 
166 
9.0 
145 
7.4 
130 
16.5 
197 
Std
Deviation 
3.9 
39 
2.9 
30 
2.1 
25 
1.6 
25 
1.2 
27 
5.1 
44 
Minimum 
6 
111 
6 
111 
6 
108 
5 
94 
4 
74 
6 
111 
Maximum 
20 
259 
17 
235 
14 
201 
11 
182 
9 
174 
25 
269 
C. Furrow
Surface Irrigation System @ 70% Application Efficiency on 160 acres
(FS70%)


Frequency 
3” in 12 days 
3” in 15 days 
3” in 18 days 
3” in 24 days 
3” in 30 days 
Full Irrigation 

GPM Rate 
754 gpm 
603 gpm 
503 gpm 
377 gpm 
302 gpm 


Average 
16.4 
174 
14.4 
160 
13.0 
149 
10.6 
132 
8.4 
118 
20.2 
197 
Std
Deviation 
4.2 
32 
3.4 
28 
2.9 
27 
2.1 
28 
1.5 
30 
6.2 
44 
Minimum 
6 
103 
6 
88 
5 
75 
4 
60 
3 
50 
6 
111 
Maximum 
21 
233 
18 
203 
15 
181 
12 
171 
9 
162 
30 
269 
a. Based on
19721998 climatic conditions at the Northwest Research Extension Center in
Colby, Kansas, and on the Stone et al. (1995) corn yield prediction model.
Regression equations are generated for yields as related to
irrigation capacity. This allows for the calculation of corn yields for
specific irrigation well capacities ranging from 200 to 700 gpm for the three
alternative irrigation systems (Figure 1). This perspective is important to
decision makers in the Central Great Plains of Kansas who often are dealing
with wells that have pumping capacities in this range. Projected annual
average corn yields for CP100% ranged from 3 to 11 bu. per acre higher than
for CP85% corn yields across of the range of well capacities considered here
(i.e., 200 to 600 gpm for center pivots) on 125 acre fields. However, average
corn yields for FS70% on 160 acre fields are from 28 to 33 bu. per acre lower
than CP85% yields for wells in the 300 to 600 gpm pumping capacity range. The
impact of lower furrow surfaceirrigated corn yields on this analysis of
conversion profitability depends in part on how profitable the nonirrigated
crop production on the 35 acres in the center pivot corners is. No 200 gpm
yield outcomes are presented for FS70%, and no 700 gpm yield outcomes are
presented for CP100% and CP85% because this would require extrapolation beyond
the range of the generated equations.
Figure
1. Irrigated Corn Yields as affected by Well Pumping Capacity, Irrigation
System and Application Efficiency.
Regression equations are also generated for annual aftertax net returns to
land, labor and management as related to irrigation capacity for the three
irrigation systems. The results are shown in Table 4 and Figure 2. These
findings indicate that it is profitable to convert from furrow surface
irrigation to center pivot irrigation systems, given the yield results and
costreturn assumptions used in this study. At 600 gpm well pumping
capacities, both the center pivot irrigation systems examined have $6 to $12
per acre annual net returns advantages over the furrow surface irrigation
system. As well pumping capacity declines to 300 gpm, the advantage of center
pivot systems over furrow surface irrigation increases to $25 per acre and $12
per acre for 100% and 85% efficient center pivots, respectively.
(Returns to Land, Labor, and Management)

Center Pivot 100% Efficiency 
Center Pivot 85% Efficiency 
Furrow Surface70%
Efficiency 

Pump Capacity (gpm) 
Total Net Revenue 
Net Per Acre 
Total Net Revenue 
Net Per Acre 
Total Net Revenue 
Net Per Acre 
200 
$2,063 
$13 
$408 
$3 


300 
6,566 
41 
4,516 
28 
$2,519 
$16 
400 
9,783 
61 
7,716 
48 
5,602 
35 
500 
11,714 
73 
10,009 
63 
8,253 
52 
600 
12,360 
77 
11,396 
71 
10,473 
65 
700 




12,262 
77 
Figure 2. Aftertax Net Returns for
Alternative Irrigation Systems Per Acre
(Returns to
Land, Labor and Management)
Williams, J. R., R. V. Llewelyn, M. S. Reed, F. R.
Lamm, and D. R. Delano. 1996.
“Economic Analysis of Alternative Irrigation Systems for Continuous
Corn and Grain Sorghum in Western Kansas”. Report of Progress no. 766.
Agricultural Experiment Station, Kansas State University, Manhattan, Kansas.