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|\/IAQ I 1955
EIXPERIIVIENT STATION
LIBRARY
By EARL G. WELCH
Circular 528
UNIVERSITY OF KENTUCKY
College of Agriculrure ond Home Economics
Agricultural Extension Division
l FRANK J. WELCH, Dean and Director

C O N T E N T S
k
Page Page ,
frequency of Drouth Periods ..V,,. 3 Cost of Irrigation Systems .4.....V . ..... I. I2
Equipment ..........,,...,. . ..,....... . ...,...4 I2
W*·¤* Cm *0 ‘"*¤·=*¤ — V ——-——rr~— » 4 Operation i_....yy..._.y _ y..t_..ty _ .,,.,.i.ii.. 12
Corn V ..,r....V 4 ·
Airurru U r V_·_4 5 Selecting an Irrigation System .......... I3 _
T°b°cC° · · · ---» V - ·· 5 Major Items of Irrigation System .... . I4 l
Puslule »- · ~ v-·v · --··iv---· 7 Centrifugal Pump .. ,... . .4..y............,. I4
Turbine Pumps .r... V .... . ..,.....,...,...,.y,. I5
Tm °*····* ¤··<* “¤"‘€* -v»-- » eese--- 8 Power P ,,ttt,..rr,...rr ,y.ry.,,. j ,,.rr,.y,...... ie
Frequency Oi irriguriori __ rV___r_ iV___ 8 Pipe Sizes .. .. i,.i ,....i , ...ii . ..,..4. `I7
Sprinklers r..i...i.....i .. ...r.........,.., I8
*‘¤*·= ¤* A¤¤‘*¤¤**¤·· ~-r»- e i-v»-· » -»--·---i-—~- 9 Vertical me .........,... .,...,...._..._r.... is
A¤‘°¤¤I' 0I W¤I€*’ *° APPIY ------»--· I0 What a Farmer Should Know About
Designing His Irrigation System .... 20
Ev¤¤¤r¤*i¤¤ LMS We --i· M »-r»--»-- - r»--ii *0 wdree Needed ,...,.....,.....,...,.....,.,. I 20 .
Sources of Water .. ,... V .. .. ,..i ll Water Rights Legislation ..,.. e ,..i,........ 22

IRRIGATION IN KENTUCKY
By Earl G. Welch
Irrigation is not a new practice in Kentucky. Farmers here,
as in all states east of the Mississippi River, have long sought
for a method of overcoming the ill effects of drouth periods-
’ even those of comparatively short duration, which occur almost
every year. For many years, they have felt the need of Sll]_)-
plementing natural rainfall by irrigation. Truck farmers have
installed permanent overhead sprinkler systems on level land of
_ high productivity with very satisfactory results even though the
_ cost per acre of the installation was much higher than the cost
of the portable pipe sprinkler system now becoming popular.
Where water is available, or can be made available, sprinkler
irrigation may become a very popular and profitable practice.
The practice of irrigation by flooding common in western
states is not practical in Kentucky because of the stateis rolling
I topography and the limited supply of water. The development
of centrifugal irrigation pumps, lightweight portable pipe with
automatic couplers, and rotary sprinklers has made it possible
to irrigate rolling land economically.
l FREQUENCY OF DROUTH PERIODS
Even though the average annual total rainfall is about 44
inches in the eastern part of the state and 48 inches in the west-
ern, its uneven distribution results in dry periods practically
every year, retarding plant growth and depressing both the yield
` and quality of farm crops. During the period 1938-48 there
were no great variations from the normal annual precipitation.
However, the average number of drouth periods of 14 days or
. more during which there was no more than % inch of rainfall
in any 24-hour period were as follows;
"__“T1T—;;i }3YH»QiiQT,}L}i.ETiT EETEE ’
Length of drouth fii"*MV*l£z1.s·lcr11 Ken/u@ \Vcs!gn Kcnluckgn
14 days or longer 3.8 4.5
21 days or longer 3.0 2.7
28 days or longer 1.0 1.()
Statewide, longer drouth periods of several months, duration,
‘ such as those of 1930, 1936, 1943, and 1951-54 are not unusual.
Successive drouth years also are not unusual.
3

V1
Normally the average rainfall per month for the early months
of the growing season is considerably greater than for the months
at the end of the growing seasons. The average rainfall in
western Kentucky for March, April, May and ]une is 4.40 inches
per month. For ]uly, August, September and October it is about
25 percent less, or 3.23 inches. For the eastern part of the state
the average rainfall during March, April, May and ]une is 4.06
inches per month and for ]uly, August, September and October ‘*
3.28 inches or about 2() percent less. As a rule, more rainfall is
required during the latter part of the growing season because
( l) there is a greater percentage of evaporation from the soil ~
during hot weather, (2) a greater amount of moisture is required .
by spring—seedcd plants as they near maturity and are producing .
seed and (3) a greater amount of forage is required by young
animals as they increase in age. Supplemental irrigation is of
value in meeting those requirements.
WHAT CROPS TO IRRIGATE
As a general rule, crops of a high cash value per acre, such
as vegetables, berries, and tobacco, when grown on productive
soil, will give the greatest return from irrigation. The irrigation
of pasture harvested by dairy cattle returns greater dividends ·
than that pastured by beef cattle because of the greater per
acre value of the marketable product. Up to 1954, farmers have
reported supplemental irrigation in Kentucky to be profitable
on truck crops including Irish potatoes; also on tobacco, pasture,
alfalfa, corn and berries. The irrigation of fall seedings of grain, 4
grasses and legumes guarantees quick germination, and rapid
growth, thus reducing the hazard of loss of seed, labor and crop
resulting from lack of moisture and guaranteeing an early vege-
tative cover to protect the soil from leaching and erosion. ‘
Corn
irrigation of corn has been quitc profitable when the crop
was planted in fertile soil and, especially, when planted for the
production of hybrid seed. The corn plant up to the tasseling
stage does not require much moisture, and seldom is it necessary
to irrigate until a week before the tassels begin to form. How-
ever. the plants should not be permitted to discontinue growth -
because of the lack of soil moisture. The soil should contain an
ample supply of moisture from the beginning of tasseling to the

5
end of silking. Irrigation after that time 1nay result in a slight
increase in yield but probably not enough to pay for the cost
of irrigation. The labor requirements for moving laterals in tall
·corn is about twice that for the same operation on low-growing
crops, or about 2 man-hours per acre. Where corn is of average
height at tasseling time lateral pipe may be moved by two men
carrying one or two lengths of pipe held above their heads. In
' very high corn forked sticks may be required to raise pipe above
the top of corn plants.
Alfalfa
. Probably little increase in yield will be obtained by irrigating
the first cutting of alfalfa in Kentucky. The irrigation of other
cuttings may be profitable unless rainfall is normal, provided the
soil is not deficient in plant food. In the dry fall seasons of 1952
- and 1953 irrigation of alfalfa after the second and third cuttings
resulted in good third and fourth cuttings. The results from the
. irrigation of fall seedings which might otherwise have failed or
resulted in poor stands because of the lack of moisture, have
been quite pleasing to farmers not only because of increased
yields the following year, but because the chances of loss of
~ labor and seed are greatly reduced.
Tobacco
Tobacco is a crop of a high cash value per acre and is usually
grown in fertile soil. Therefore, it is one of those crops which
l has been most profitably irrigated in Kentucky. Authorities on
the production of burley tobacco state that “rapid growth, espe-
cially in the early part of the growing season, is necessary to
r produce the thin, smooth, colory grades of burley tobacco now
_ in greatest demand. Some of the finest crops are made in 75
days or less. To secure such rapid growth, the soil must be
capable of supplying large amounts of available plant food in a
relatively short time.”
An adequate supply of soil moisture, as well as that of plant
food, is essential to the continuous rapid growth of tobacco or
any other crop. Supplemental irrigation therefore eliminates the
lack of soil moisture as a factor limiting either the quantity or
l quality of tobacco produced.
To aid in determining if the irrigation of tobacco is a profit-
able practice in Kentucky, farmers were asked to report on the

fi
V$ ° —<· ‘ .
,y»·.’· I. .· , :_~,.·j' :5; · L} . P. . . { s.:?¢,I ty n .2%.:.
(I Ag md V/v‘<»·;· ~/ f’J‘.;!7(q;g’§if',§ ‘_ »I; Q1, -rA?,}l ue;] {I 1 _ 'y
. , " , " 4 `.‘9'(\{ *7; 5574 1;***)} `}'i(Y A, H,_7{ , ·•_ E, ivy
~;>—1>>·‘ @·*:~»{ +3 ·{g» ·~~·¢’-: » * ·f··
·‘ ‘ `~· {1 ’ 'Y ·· r éiE~‘<·,• 4 ; hi
.} g;\;4 •. i. .. ·¤ 5
. ·‘,~ `~ $$1- J. i*{_i‘Y fl? in ·,_ {
*‘Y”ii"$?¢< ;"§~§"* `“ . is A4 I ‘ *,1 Q
" P- *3 ·—— 11. `· ~ ' \· ` *21 . . if
\ It _:` ¢ V;} · _,_l Jn}, l vi ; V. Y I (Y ,,`/
° v" `· V 4 jj ~., ¤ I ..4V
V" A .~ v_ , 4 * g \\. yi
" • ' i · 2. ' *· ,. - .
’ 1 2*, Ip V · V “ ~ " ` w'q‘·
. _ V. 1. ' /"‘• I ·· - ;. ’
· ~. ‘ .1’ 5** ` M ;: .‘* n t ’ _
` it ~ ~ · - ‘* `. . . I r' . ” “
a“"'t·f¥; ;,v··l§·’. .1 . ~ »
‘ to 11.* . f•* ' ,· M mi,
»,O .’ *·_ ¤ ` . t ‘ [ —_= ’
yp _ '~ yy V 4; r .?» .‘ q`
1 .·_ _ · V A I ; x. ‘ .
Fig. 1- A typical field of tobacco that has been irrigated. Note the sprinkler
in the right center of the picture. Tobacco fields are generally irrigated
two or three times with l to 1% inches of water each time. Durin r the three
. . . t·
years, 1951-53, irrigation increased the income of tobacco for 69 crops in 251
counties an average ol` $408.17 an acre.
yields and selling prices ol irrigated tobacco grown on their
farms in 1951, 1952 and 1953 where fertilization, housing and
selling conditions were similar for irrigated and non-irrigated
tobacco. The results ol these farm tests are given in Table 1.
Much interest has been expressed in records which would
indicate the benefits ot irrigation during years when monthly .
rainfall ll\'(‘1`1lg(‘S more normal.
Table l.- Results of Farm Tobacco lrrigation Tests°1‘ l
. .... ...jf;L7 YZTNY., " L j"'f,';Q,.'1“T,.? L
__ N V iiigggripiL g f¥iN()N-Il11lI(}.·\TEl)
Year Ncrcrnps Counties .·\v.lb. ;\. .·\\‘.price .·\\‘.$ ;\. .·\y·.ll». .»\. ;\\‘.price ;\v.S ;\.
1951 12 8 21181 $61.211 $127:3.47 1493 $55.911 $820.35 »
1952 15 111 1979 54.011 lflfiil.69 1296 49.58 6~1(1.(l(1
195:3 -12 19 1959 55.92 11195.99 1398 51.82 747.31
1951 1
19521 69 25 21111:3 57.114 1141116 1:396 52.117 735.89
19531
Tpqrllainfall, during: the growing seasons of 17951-52 and 1953 was below normal, and the
tlepartnre from even distribution in the state as a whole was greater than in a normal year.

In 1953 records were kept in Shelby County on 10 farms,
growing an average of 8 acres of tobacco, where the amount of
rainfall was considered ideal for the production of tobacco. Rain-
fall for April, May and ]une was slightly above normal and only
().10 inch less than normal for ]uly. Rainfall following ]uly was
below normal. Non-irrigated check areas were establishd in
each field, and records of yields, selling prices, and cost were
` calculated by a representative of the Department of Agricultural
Economics.
A summary of the results on the 10 farms for 1953 show the
average investment in irrigation equipment to have been $2500,
with an additional investment of $2000 per farm for the con-
struction of an irrigation reservoir. The amount of water applied
by tobacco growers varied from a total of 1.5 to 4.25 inches in
» one or two applications at periods when it appeared the soil
- was becoming dry. Yields per acre on the irrigated land were
2,204 pounds and on the non—irrigated land 2,032 pounds. The
average selling price was $62.29 per 100 pounds on irrigated
‘ land and $58.80 on the non—irrigated.
The total increase in value per acre of the irrigated over the
non—irrigated tobacco was $178.03. The average total cost of
irrigation based on an investment of $4500 including interest,
depreciation, labor, taxes and operating expense was $22.94 per
acre, leaving a net increased income per acre of $155.09. The
total net increase for the 8 acres was $1240.72 on the investment
of $4500. Seemingly this is an adequate return for supplemental
irrigation in a season when rainfall was considered ideal for the
production of tobacco.
Many farmers did not buy irrigation systems in 1952 until
the 1952 drouth was well advanced and, therefore, did not irri-
» gate tobacco until after August 1. The effect of the time of the
’ first irrigation on the average selling price of tobacco is indicated
in Table 2.
` Table 2.- Effect of Time of First Irrigation on Average Selling Price——l952

18 Before August 1 $58.20/100 lb.
_ WVS53.44/100 A i
Pasture
The irrigation of pasture on well fertilized soils has been
profitable, especially when the pasture was grazed by dairy cattle
because the forage converted into milk has a greater value per

8
acre than the same forage used to produce meat. Contributing
factors are the maintenance of legumes in the pasture mixture,
an extension of the grazing season in the late fall months, and
a more nearly complete ground cover.
A definite schedule for irrigation of pasture should be estab-
lished and maintained during the season, and the number and
frequency of applications will depend on rainfall. If irrigation
is limited by lack of water or labor it will be more profitable A
to apply late applications to fall seedings of grain and legumes
than to established pastures. The occasional irrigation of estab-
lished pastures after they have suffered from a lack of moisture s *
will help prevent further damage, but will probably not increase ·
their carrying capacity to any great extent. Farm experience ·
indicates it is more profitable to irrigate and fertilize a limited A
area properly than to cover a greater area with an insufficient .
amount of water and fertilizer.
TRUCK CROPS AND BERRIES _
Truck farmers in commercial areas, such as ]efferson County,
have been practicing irrigation by sprinkling for many years.
irrigation not only increases yields but the quality of the produce.
Present methods of marketing and preserving vegetables by
freezing require that truck crops be of high quality, otherwise
there is little demand for them.
()n july lf), l954, during the extremely hot and dry period
of early summer, radio station VVHAS reported that the only
tomatoes reaching the Louisville market from local growers _
were from irrigated plants. »
FREQUENCY OF IRRIGATION A
ln Kentucky, irrigation must be considered a supplement to I
rainfall. lt is a guarantee that crop yield and quality need not V
be materially reduced by drouth periods. The total precipitation
(irrigation plus rainfall) which will be most profitable has not `
been determined for many farm crops in states east of the Mis-
sissippi River. As a rule. crops such as alfalfa require a heavy
total application at comparatively long intervals, while shallow-
rooted crops require a lighter application at shorter intervals.
All crops should be irrigated before they have suffered from ‘
a lack of moisture. Otherwise. they never fully recover in yield
or quality. lf irrigation is not started in a field requiring several

9
days to i1*1*igate until the lack of moisture is appa1*ent the crop
011 so111e portio11 of tl1e field is likely to he da111aged severely
before soil moisture is replenished.
It is usually u11wise to delay ir1*igatio11 during l1ot dry weather
i11 anticipation of rainfall. Even tl1ougl1 l'21l1] 111ay fall it 111ay be
inadequate to supply the soil with ]]]OlStll1`G t0 the desi1*ed depth,
01* a high perce11tage of it may be evapo1*ated i11t0 tl1e ai1*. Tl1e
1*ain may be intense fo1* a short pe1*iod of time, 1'(iSllllIl1]g i11 a
very sl1allow penetration, because of a high percentage of runoff.
So111e type of soil 1]lOlStllI`€ 1nete1* should be available for
‘ indicating the kllHOU1]t of moisture in the soil at various depths.
` A 1*ain gage should be installed 011 every farm having an irriga-
‘ tio11 system as a cheek 011 the a111ount of rainfall received as
compa1*ed with that 1*eported at tl1e nearest weatl1e1* station.
Frequently tl1e1*e is a wide variation between tl1e amount of
rainfall on one farm and that of neighboring farms and recording
T stations.
. RATE OF APPLICATION
Most of tl1e soils i11 Kentucky are classihed as having “1l)(}-
dium” texture, a11d Wll(;‘]] 11ot cove1*ed by vegetation tl1ey will
absorb water applied by a sprinkler system at a 1*ate of from 0.4
to 0.5 i11ch per hour EI.H(l will hold about 1.5 inches of water per
foot of depth. In lighter soils having more organic matter, such
as tl1ose fou11d i11 some 1'l\`(‘l` bottoms, the rate of absorption of
bare soil 1nay he i11c1*eased to 0.75 inch per l]()lll` and the water-
l1oldi11g capacity decreased slightly. \Vhere l]CU.\’lC1'-tlltllI-il\'(‘l`tl§.§(‘
V ` soils exist, such as the Eden clays. tl1c 1`ilt(3 of absorption may
be as low as 0.25 i11cl1 pe1* hour and tl1e \N2lt(¥l'-l]()l(llllg capacity
reduced to 1 inch pe1* foot of depth. Soils having an absorption
. 1*ate of as little as 0.25 inch per hour and poo1* internal and sur-
face drainage may become water-logged by a combination ol`
4 rai11fall following irrigation. There is little danger tl1at rainfall
following irrigation of well drained soils will be injurious to
l c1*ops during the growing season except possibly in the case of
tobacco fertilized with too 1nucl1 nit1*ogen. Then the tobacco
lllkly co11tinue to gl'()W whe11 it should be ripening.
Seve1*al different types of soil may be found on the sanie
farm and even in the same field. lt is not practical to design
T 01* operate an irrigation system fo1* all of these varying conditions.
An application rate of 0.3 or 0.4 inch per hour will be satisfactory
for most ba1*e soils in Kentucky. The rate of application may be

I0
increased for a given pumping condition by increasing the size
of nozzles in sprinklers and sprinkler operating pressures, pro-
vided some reserve capacity is provided for in the pumping unit.
AMOUNT OF WATER TO APPLY
The amount of water to apply at any one time will vary
with the crop to be irrigated, the depth of root system and the
.amount of moisture in the soil at root depth. The following ap-
plication at one irrigation is suggested as a general guide for
different types of crops:
Xlixed grass-legume pasture 1M2"-2"
Alfalfa 2”-B" .
Vegetables I"-1%"
Tobacco (First irrigation soon after setting) IF/Q"-I" _ I
Tobacco I"-1%" ;
Boot Crops I"-2"
New seeding of grains, grasses, and legumes I"
A common practice is to make a heavy application to a deep-
rooted crop, such as alfalfa. From 2 to 3 inches will supply the V
needs for one cutting. Truck farmers apply about one inch to
.shallow—rooted crops following a week or I() days during which
natural rainfall has not equaled {Q inch.
The feel of the soil taken from the root zone is often used
to determine the need of moisture and show when a sufficient
amount has been applied. When a sample of soil is crumbly
but will not hold together, the amount of moisture is “low.”
If the soil is cmmbly but will hold together, the moisture con-
dition is considered “fair.” \Vhen the soil forms a hall which
will stick together, the moisture condition is considered "good.” . Q
If the soil forms a ball and is pliable, sticks readily, and clear
water comes to the surface when the ball is squeezed, the mois-
ture condition is considered “excellent.” Irrigation should begin r ‘
when the moisture content lowers to “fair” and be discontinued
when it reaches "excellent."
EVAPORATION LOSS
Evaporation losses may be as high as 20 percent of the water
delivered by sprinklers in very hot, dry weather. Irrigation in
the late aftemoon or at night reduces these losses. If an exact

l I
amount of water is to be applied. the loss from evaporation may
be offset by extending the period of operation.
SOURCES OF WATER
Wells, rivers, creeks, artificial lakes, and farm reservoirs are
potential sources of water for irrigation. Even though some of
the sources may not supply enough water for irrigation during
an extended drouth period, they will supply a sufficient amount
to supplement rainfall during the average year of unevenly dis-
tributed rainfall.
A farmer should make an estimate of the number of acre-
_ inches required for his crop or crops (an acre-inch is the amount
_ of water required to cover an acre to a depth of one inch, or
- 27,154 gallons) as the preliminary step in planning for a system
of irrigation. If reservoirs are to be constructed exclusively for
storing irrigation water the cost of the reservoir should be in-
e eluded in the investment for irrigation. On an average, 6 acre-
inches will be required for each acre to be irrigated excepting
pasture. From 8 to 16 inches 1nay be required for pasture during
a very dry year. If the water is stored in reservoirs, at least 2
acre-inches should be stored for each acre-inch used. This allows
for evaporation and loss by seepage. If the reservoir is to supply
water for livestock, an additional allowance may be made for it.
The percentage of the water contained in a large irrigation
reservoir that will be consumed by the stock will be very low.
Example: To provide water for irrigating 9 acres of tobacco
with four applications of 1 inch each, a total of 36 acre-inches
- would be required. Twice 36 acre-inches or 72 aere—inches should
A be stored. A reservoir one acre in area with an average depth
of 6 feet (72 inches) would contain 72 acre-inches and supply
water for irrigating 9 acres oi tobacco with a 50 percent allow-
A ance for seepage, evaporation and lixestoek.
Even though it is possible that rainfall would replenish the
supply of water in the reservoir during the growing season, no
E dependence should be placed in this occurring. In some in-
stances, a reservoir may be refilled from a stream with irrigation
pumping equipment. ln hilly land, reservoirs built at high ele-
vations may be used to operate sprinklers at lower elevations,
by gravity How. Low pressure-low volume per minute sprinklers
l may be used. Since no motor power is required to operate

12
sprinklers they can be operated 2-1 hours per day to maintain a
high rate of coverage in acres per day.
In most of the limestone counties of Kentucky. deep or shal-
low wells do not supply water at a rate sufficient for irrigation
purposes. However, along the Ohio river beds and in the counties
west of the Tennessee River, wells with a pumping capacity
of 50 to 200 gallons per minute or more may be obtained at a
depth of from 10() to 200 feet.
A deep-well turbine pump is used to deliver water under
pressure from deep wells. In some sections of the Ohio river
counties, shallow driven wells have a capacity of about 25 gal-
lons per minute. \Vhcre the vertical lift does not exceed 15 feet, .
several of these wells may be connected at ground level and _
water delivered by one centrifugal irrigation pump to the dis- _
tribution lines. Savings in the cost of equipment and of operating —
expense may be made if sources of irrigation water and areas
to be irrigated are not far distant. Farm reservoirs to be con-
structed can frequently be located near tobacco fields. .
COST OF IRRIGATION SYSTEMS
Equipment
The cost of irrigation equipment cannot be accurately stated
on the per acre basis except for an individual system and then
only after the maximum number of acres of all crops to be irri-
gated and the cost of the irrigation system with its capacity to
cover the required acreage with a given amount of water in a
given period of time has been calculated.
The investment in complete irrigation systems has ranged ·
from about $1,000 to as high as $15,000. Several irrigation com- l
panics are available for designing irrigation systems and sub-
mitting estimates of cost. .
In checking costs submitted by various companies. one should
compare carefully the following things: the capacity of pump
and engine or motor, the munber and size of sprinklers, the
amount and size of pipe, the proposed spacing of sprinklers and ’
lateral lines. and the rate of application in inches per hour.
Operation
Irrigation is recommended for crops of a high cash value per _
acre that are grown on fertile soils. Such crops as tobacco. truck

1:3
crops, hybrid seed corn and berries can doubtless be irrigated
profitably even though the amounts of water pumped annually
by an irrigation system is not sufficient to keep costs to a mini-
mum.
The Agricultural Economics Department of the College of
Agriculture and Home Economics has summarized cost data
from farmers who irrigated tobacco and other crops in 1951.
' Total costs ranged fro1n as low as $1.67 per acre-inch for one
farmer who had an investment of $1,863 and pumped 254 acre-
inches of water to as high as $34.79 per acre-inch for another
who had an investment of $875 but who pumped only 3.6 acre-
inches.
· I A group of 12 farmers had a total cost of from $13.71 down
· to $1.67 per acre-inch. Probably the majority of farmers will
Q have total costs which fall within the range of this group.
The amount of tobacco required to pay for irrigation is indi-
_ cated by a group of 12 farmers whose total cost varied from
` $1.67 per acre-inch to $13.71 per acre-inch. Irrigated tobacco
A on all test farms sold for $61.20 per 1()0 pounds in 1951; using
this selling price, 2.75 pounds of tobacco was required to offset
the cost of an acre-inch of water on the farm having a cost of
$1.67 per acre-inch and 22.5 pounds on the farm having the high
total cost of $13.71 per acre-inch.
In 1951, no farmer used more than 4.5 acre-inches of water
per acre. If it is assumed that the farmers having the highest
and lowest costs used 4.5 inches on each acre, the cost range
in terms of tobacco sold at the average price of irrigating tobacco
in 1951 was from 12.5 pounds to 101 pounds per acre.
~ The average increase in yield of tobacco resulting from irri-
` gation on test farms in 1951 was 588 pounds per acre.
I SELECTING AN IRRIGATION SYSTEM
An irrigation system, to be of maximum service at a minimum
of cost and operating expense, should be designed for the con-
` ditions under which it is to operate. It should be designed by a
person familiar with cropping and soil fertilization practices as
well as the engineering principles involved in pumping water
in varying quantities to different elevations. The information
required for planning an irrigation system may be indicated on
` a map of the farm drawn to scale. It should show the Helds to
be irrigated, the crops to be grown, the location and sources

14
of water, with thc amotmt of water available in terms of acre-
inches, cubic feet, or gallons in the case of lakes or reservoirs,
and in gallons per minute in case of wells, streams, and springs.
The elevation in feet of the high and low points of each field
above sources of water is needed. Distances may be scaled from
the map for preliminary estimates.
If no map is available, the data above should be obtained
and shown on a sketch of the farm. "
MAJOR ITEMS OF IRRIGATION SYSTEM
The ma'or warts of an irri ration s stem are the num ), main .
1 1
pipe lines with couplers leading to fields to be irrigated, sprinkler _ ,
lines, and sprinklers. Parts including Ys, T’s, reducers, valves, ` _
end plugs and suction hose or pipe are also required. Gages
to indicate pressure in pounds per square inch at the pump and
at lateral lines are essential where a system is used under dif-
ferent pumping conditions of volume and pressure. .
Centrifugal Pump
.·\n irritation nun) is usuall a centrifural yum) cavablc
l I Y is 1 1 l
of delivering a large volume of water against high pressure. The
capacity in gallons per minute (CPM) varies with the pressure
in pounds per square inch (PSI) against which water is to be
delivered. That is, the higher the pressure needed the lower
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Ic ‘ - • .
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Fig. 2.- An irrigation pump having zi direct-comrected engine with
il\l[0IIl1l[I(` SRIKCIT (`0Il(I`()IS, A

15
will be the capacity in GPM. For example, a pump may be rated
at 225 GPM at 85 PSI, or at 400 CPM at 40 PSI. A smaller
capacity pump may furnish 80 CPM at 75 PSI, or 150 GPM at
40 PSI. The capacity varies with the speed of the pump, which
in turn is controlled by the speed of the engine or motor which
drives it where the power is connected directly to the pump
and also by the size of pulleys in other cases.
· The installation of automatic safety controls and priming de-
vices is made simple where gas engines are directly connected
to a centrifugal pump. These safety devices stop the engine in
case a shortage of oil or water causes overheating and prevents
. excessive speeds if for any reason water is not available to the
. pump.
The maximum recommended vertical lift of a centrifugal
pump is 15 feet.
‘ Turbine Pumps
Turbine pumps are used in deep wells where the lift from
low water level to ground level exceeds 15 or 20 feet. They are
usually driven by electric motors. Turbine pumps may be used
to advantage where there is a deep well of sufficient capacity
in gallons per minute, adequate electric power is available, and
the anticipated total net income from irrigation is great enough
to justify the investment.
Power
. A large majority of irrigation pumps are driven by gasoline
engines which are connected directly to the pump. All internal
combustion engines as supplied by manufacturers are of such
horsepower as to hold up under specified operating conditions
at a given speed. If they are operated at a higher speed satis-
· . factory performance over a long period of time should not be
expected. The continuous performance load placed on a gasoline
engine should not exceed 70 to 80 percent of its maximum rated
horsepower.
A deisel engine may be operated more economically than
a gasoline engine, but the investment is considerably greater.
Where 40 horsepower or more are required to operate a pump
and the irrigation system will be operated 350 hours a year or
more, a deisel engine may prove a more economical source of
A power than a gasoline engine.

16
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