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IRRIGATION

OF CORN

THE

EASTERN

UNITED STATES

Agriculture Handbook No. 140

UNITED STATES DEPARTMENT OF AGRICULTURE
CONTENTS

Page

Does irrigation Of corn pay? 2

Field corn for grain j

Sweet corn ^

IVIanagement practices change with irrigation 5

When to irrigate I

Judging from appearance of soil or plants o

Use of soil moisture meters '

Use of weather records '

Irrigation methods ^

Sprinkler method ^

Furrow method *"

Amount and rate to use - |2

Sprinkler application j^

Furrow application «2

General recommendations 13

Literature cited 13

Washington, D. C. Issued October 1958

For sale by the Superintendent of Documents, Government Printing Office, Washington 25, D. 0. Price 10 cents
IRRIGATION OF CORN

IN THE EASTERN UNITED STATES

By V. C. JAMISON and O. W. BEALE,

Soil Scientists, Soil and Water Conservation Research Division, Agricultural

Research Service

Irrigation of crops in the eastern

United States is often needed, although the area has a humid climate. However, in many sections

of the area, water for irrigation is

scarce and the farmer must consider how he can use the supply

most advantageously.

Even where the average total annual rainfall exceeds 50 inches, frequent drought periods of 2 weeks

or more occur during crop growing

seasons (6, 8, 18, 28, 29, 30)}

Much of the rainfall during the

summer comes in storms of short

duration and high intensity (31).

On the fine-textured soils with a low

rate of water intake, some rain that

falls is lost as runoft"; on coarsetextured soils, some rainfall is lost

by rapid drainage to depths below

the root zone. In addition to this,

considerable quantities of rainfall

moisture evaporate from the soil

surface regardless of soil texture.

Growing competition with industrial and domestic users can be expected to reduce available sources

of water for irrigation {20, 25),

This competition for water indicates that efficient management of

agricultural and industrial water

usage is essential if the supply is to

satisfy the needs. Whether water

for irrigation comes from streams,

reservoirs, wells, or farm ponds, it

1 Italic numbers in parentheses refer to

Literature Cited, p. 13.

465897°—58

should be used on crops that will

give highest returns per acre.

The quantity of water needed to

produce a corn crop will depend on

the climate at different locations.

In some seasons and locations when

there are long periods of cloudless

skies and the temperature is high

during dry windy days, water lost

from an acre of growing corn will

be more than when the sky is cloudy

and the air is moist and relatively

cool. In Missouri corn irrigation

tests, total water loss by evaporation from soil and transpiration

from plants (évapotranspiration) in

1954 and 1955 was estimated at 25

inches of water per acre when the

soil was kept moist throughout the

growing season. Data supplied by

Van Bavel and Lillard^s approximate values (29) indicate about 17

inches of water would be lost from

an acre of corn during a 120-day

growing season in the mountains of

Virginia.

The water used by a crop of corn

must come from rainfall stored in

the soil before planting and that

supplied by rainfall and irrigation

or by irrigation while it is growing.

In the semiarid regions of the

United States, precipitation is generally insufficient to replenish storage in the root zone, and irrigation

before planting is sometimes practiced. However, in the humid

East, the soil storage reservoir is

usually filled to near ^afield capacity" at planting time, and preseason

irrigation is not necessary. Field

capacity is the moisture retained in
AGR. HANDBOOK 140. U. S. DEPT. OF AGRICrLTURE

a soil with normal drainage about 2

days after the field has been

thoroughly wetted by rain or by

irrigation.

In order to make full use of the

available stored moisture, roots

must grow into and ramify the soil

mass. The available moisture storage capacity of a soil is usually the

maximum moisture that can be

released to plant roots from the field

capacity point to the permanent

wilting point. The permanent wilting point is the amount of soil

moisture at which most crop plants

wilt when actively growing roots

are well distributed in the soil mass.

The total quantity of water that

is available for use by the growing

crop from soil storage depends on

the storage capacity of the soil and

on the root distribution of the

plants within the soil. A sandy

soil mav store about 0.7 inch of

available water per foot of soil

depth, while a silt loam will retain

about 2.2 inches {15). Compact

layers in some soils {IS) may

reduce water intake from winter

rains and limit preseason storage

and so add to the drought hazard

in dry summers. A compact layer

may also limit root growth into the

subsoil and reduce the supply of

storage water that is available to

the crop. Corn roots are usually

distributed so that less than onefourth of the total withdrawal is

from depths below 3 feet. During

periods of extreme drought and

with no irrigation, withdrawal of

moisture below 3 feet is accompanied by slower growth and loss

in yields. Even from soils with

best storage of water, no more than

10 to 12 inches of stored water can

be drawn hj a corn crop unless

replenished by rain or irrigation.

DOES IRRIGATION OF CORN PAY?

Unirrigated corn crops were near

failures in many parts of the

eastern United States for 4 of the

10 years 1946-56, and yields were

sharply reduced in other years

(fig. 1). On the other hand, rainfall has been ample in most of the

East in some years and irrigation

has had little or no effect on corn

production. Supplemental irrigation of corn will vary from occasional use to save a crop or to tide

over short drought periods (4, 8, 9,

11, 12, IS, 16, 17, 18, 19, 2U 22,

23, 32) to use of water on corn

nearly every season when grown on

soils of low storage capacity {1,

2, 3).

The answer to the question,

''Does irrigation of corn pay?" will

depend on the market value of the

crop, the cost of production with

and without irrigations, and upon

yields. Also, if the supply of water

is limited, as it often is in dry years,

the grower must consider on what

crops the short supply can best be

used. Corn as a cash crop would

probably have a high priority over

some other crops. However, corn

may have to give way to more

advantageous use of water on such

higher value crops as tobacco and

A^ege tables.

Field Corn for Grain

Response of field corn to irrigation in the humid East depends

upon soil and weather conditions

during the growing season and other

management practices in addition

to irrigation. In growing seasons

of low or poorly distributed rainfall,

yield increases are usually greatest

with irrigation during entire growing season, adequate fertilization,

and fairly thick stands of 15 to 18

thousand stalks per acre {6, 23).

However, the best returns per inch

of water supplied are usually with
IRRIGATION OF CORN

Figure 1.—Appearance of irrisated corn (A) and unirrigated corn (ß) in a South Carolina experimental plot, after a very dry growing season when rainfall for July and August was

2.30 inches.
AGR. HANDBOOK 140, U. S. DEPT. OF AGRICULTURE

conservative use of water during

critical dry periods, particularly

during the tasseling to early dent

staged of growth (11, 12, IS, 16,

32). Published information from

some Eastern States {1, 2, 3, 4, 17,

23, 32) show more consistent

increases in corn production with

irrigation in areas of lower summer

rainfall and on soils of low available

moisture storage capacity.

Corn uses about 50 percent of the

total available moisture in Piedmont soils of South Carolina in 8

to 10 days, and in the Coastal Plain

sandy soils in 4 to 5 days {17). In

most years increases in yield more

than pay for irrigation on a soil

like Bolivar silt loam in the Ozarks

of Arkansas {1, 2, 3), but unless

long summer droughts occur on a

soil of high available moisture storage capacity like Sharon silt loam

or NicoUet loam (23), supplemental

water applied to corn will not pay.

On upland and lowland sites in

Alabama and Georgia {9, 16), economic returns for corn irrigation

apparently can be expected only in

years of severe moisture stress at

the critical 3-week period just

before, during, and after silking.

Supplemental water has been

applied to corn during 8 of the last 9

years on Mexico silt loam at

McCredie, Mo., in the period 1948-

56. The June-through-August average rainfall was 11.04 inches, or

about 1 inch below normal for a

60-year period. The average runoff

for the 3-month summer period

during the 9 years was only 0.91

inch. An average of about two

irrigations, or 4.55 inches of water,

was applied with an average in2 The critical period of maturity of

corn is variously referred to as the

"tasseling (or silking) to early dent (or

milk) stage." The ''milk stage" is a few

days earlier and less definite than "early

dent" and probably does not include the

full critical maturing period. For consistency herein, the period is called

"tasseling to early dent stage."

crease of 77.4 bushels per acre, or

a 17.0-bushel increase for each incli

of water applied. At an estimated

cost of $3.00 per inch of water used,

each bushel increase would cost

about $0.18. On Mexico silt loam

most of the moisture withdrawal by

corn roots is restricted by the claypan to the upper 2 feet of soil. The

available moisture storage capacity

of the surface silt loam is high

(about 4 inches in the upper 2 feet).

During hot summer days water use

by corn in Missouri often exceeds

0.25 inch per day. A summer

drought of 2 to 3 weeks will result

in yield reduction, and a 30-day

drought without irrigation in midsummer will result in a corn crop

failure on this soil. Wherever a

water supply can be made available

to Mexico silt loam and used with

adequate fertility and other good

management practices, irrigation of

corn at 1957 prices should pay good

returns. Information on the probable length and duration of summer

droughts to be expected in Missouri

and elsewhere in the East will be

useful in predicting under what

price and cost levels corn irrigation

will pay. Such information is being

made available in some States {28,

29, 30),

Sweet Corn

Even though the production period for sweet corn is somewhat

shorter than for field corn, it is

often grown during spring or summer months when damaging

droughts occur (4, 18, 19). vSweet

corn is usually a high-value crop,

so that even a moderate increase in

costs for irrigation may mean a

big increase in per-acre returns.

In 2 dry years (1951, 1952) an

average increase of 614 dozen ears

per acre resulted from the supplementary application of about 8

inches of water at the Mississippi

Truck Crops Branch Station (4)-

At $0.25 per dozen this would
IRRIGATION OF CORN

mean an average net return of

$153.50 per acre for these dry

years. In the first 6 months of

1953 at this station, the total

rainfall was over 45 inches {18).

However, from May 19 there was

no rain for 31 days. During this

period about 4 inches of water

applied in two irrigations on sweet

corn increased the yield by almost

800 dozen ears per acre. Such

dry periods of 2 weeks or more

occur in Mississippi and elsewhere

throughout the humid East. In

30 years of the 41-year period

prior to 1955, droughts of 14 days

or more with less than 0.24-inch

rainfall have occurred at the Mississippi Truck Crops Branch Station during May and July, and in

26 years of this period during June.

Yields of sweet corn at the New

York State Experiment Station

(Geneva) in dry years have been

increased by more than 1 ton per

acre by irrigation (19). In other

years, like 1956 when summer rainfall was adequate, no benefit resulted from supplemental irrigation.

The tests at this location show that

irrigation in dry years increased

plant growth to silking time and

that maintenance of adequate moisture thereafter until maturity increased ear size.

MANAGEMENT PRACTICES CHANGE WITH IRRIGATION

Varieties should be selected that

are adapted to specific locations

(14)- Some corn varieties that

grow well in the coastal areas

are poor producers in the Piedmont

and mountains. Other varieties

are adapted to bottom lands and

growth of these varieties may be

retarded on uplands, owing to soil

moisture stress. Generally, irrigation has little or no effect on

lodging (13). Irrigated corn usually has better rooting to withstand wind, but lodging will increase if winds occur while the

soil is wet. Ample soil moisture,

either from rain or from irrigation,

usually causes earlier maturity for

most varieties (23).

Although yields generally increase with rainfall, high summer

temperatures, particularly in the

Middle West, seem to affect corn

yields adversely (^, 23). The number of hot days in Iowa in August

1954 and 1955 appeared to affect

yield more closely than did the

amount of rainfall. In South Carolina high temperatures (93^ to 99°

F.) over extended drought periods

during 1957 caused ''baking'' of

tassels, even where crops were

irrigated. Poor pollination resulted.

Cooler weather usually accompanies

periods of rainfall, but air temperatiu*es are not greatly inñuenced by

irrigation. On the other hand, with

excessive cloudiness during rainy

periods in some growing seasons,

the reduction in sunlight mayreduce

growth.

Areas under clear summer skies

(23) respond better to thicker

stands with irrigation than areas

of more prevalent cloudy weather.

Soil moisture, whether from rainfall or irrigation, is used most

efficiently by corn growing on

adequately fertilized soil (24)' An

application of 100 to 150 pounds of

nitrogen per acre appears to satisfy

the nitrogen requirements of irrigated corn. In addition to nitrogen, any needs for potassium and

phosphorus shown by soil tests or

direct field tests should be supplied,

following the recommendations of

the State agricultural experiment

station. Lime should be appHed

as needed to maintain a pH of

6.0 to 6.5. The choice of dolomitic
6 AGR. HANDBOOK 140, U. S. DEPT. OF AGRICULTURE

or calcic limestone will depend upon

the relative need for calcium and

magnesium in the soil. Here again,

local recommendations should be

followed.

Corn populations have been adjusted at several levels by changing

row widths and spaces between

plants in the row. When the

number of plants are much greater

than 15 to 18 thousand plants, tall

spindly and weak plants develop

that lodge easily (6, 23). Ears on

plants of populations exceeding 15

thousand are usually very small,

and prolific varieties may set only

one ear per stalk. In the humid

East best yields are obtained with

about 15 thousand plants per acre

in rows about 40 inches apart.

WHEN TO IRRIGATE

Corn should be irrigated whenever necessary for continued healthy

growth and to prevent reduction

in yields as a result of soil moisture

stress (fig. 2). The optimum soil

moisture range for corn growth

appears to be at low moisture

stress {10), or from 100 percent of

the available stored water in the

soil down to about 50 percent as

measured at the 8-inch depth.

Research in Virginia ^ and

South Carolina {17) indicates some

growth reduction in early stages

will not substantially reduce corn

yields, although the available soil

moisture may drop to near the 20-

percent level. However, such low

moisture is very critical, for corn

production from the time the plants

begin to tassel until they reach the

early dent stage (fig. 3). Corn

' Unpublished data.

irrigated only during this stage

usually produces yields almost equal

to those of corn irrigated throughout the growing season. Yield increases per inch of water applied

are greater for irrigations during

tasseling to early dent stage than

by irrigations throughout the growing season {13, 16, 32).

Judging From Appearance of Soil or Plants

Corn uses about 50 percent of the

total available moisture in Piedmont soils in 8 to 10 days, and in

Coastal Plain sandy soils in 4 to

5 days {17). On some deep silt

loam soils {23) of higher storage

capacity, ample moisture is available to corn for 2 weeks or longer.

A visual aid that may be used to

estimate soil moisture conditions is

"balhng" the soil in the hand (7).

About 50 percent or more of the

SC-Kl-lOO

Figure 2.—Yields of irrisated (left) and unirrisated com (risht) from one-fiftieth acre.
IRRIGATION OF CORN 7

, 1

Figure 3.—Field of irrigaled and unirrisated corn in South Carolina when rainfall during growing season was 6.62 inches. Irrigated corn received 6.90 inches of water during tasseling to

early dent stage. It yielded 69 bushels per acre while the unirrigated crop was a failure.

available moisture has been removed from a sandj^ loam soil when

it will not ball under hand pressure ;

from a loam or silt loam when it will

ball but is crumbly; and from a clay

or clay loam when it is slightly

pliable, but cracks appear. Corn

usually wilts in the morning and

recovers overnight when the available moisture is near the 50-percent

level. However, exceptionally high

temperatures and low humidity will

cause corn to wilt temporarily when

the soil moisture is relatively high.

Criteria for determining when to

apply water can be a combination

of these observations. The soil

should be examined for balling and

the corn leaves watched for morning wilt. The sample for the soil

observation should be taken from

about the 8-inch depth. Soil nearer

the surface may be more nearly airdry. Irrigation should not be delayed when the soil and the plants

show evidence of moisture shortage.

Delaying a needed irrigation as

much as 2 or 3 days may be detrimental to plant growth.

Use of Soil Moisture Meters

Commercially available tensiometers and electrical resistance cells

will also provide estimates of soil

moisture content. Gypsum, fiber

glass, and nylon electrical resistance

cells have been used to some extent.

If carefully calibrated in the specific

soil, these units will give estimates

of degree of moisture depletion at

a given depth.

Use of Weatlier Records

The available moisture remaining

in the soil may be determined by a

"balance" system. This method is

based on the assumption that most

crops in healthy vegetative gi-owth

on soils adequately supplied with

moisture will transpire about the

same amount of water each day

under the same weather conditions.

If values for daily water lost by

evaporation and transpiration and

the amoimt of available water that

can be stored in the root zone of the

soil are known, the time to irrigate

can be estimated to the day.

Estimates of the available storage

capacities of different soil types are

given in the Soil Conservation Service Irrigation Guides (26), where

these are available. The guides are

revised from time to time in order

to present the most reliable current

information. Where no guide is

available, the approximate available

moisture-holding capacity for differ-
8 AGR. HANDBOOK 140, U. S. DEPT. OF AGRICULTURE

ent soil textxires, as given below, table 1. Use of the balance system

may be used. to determine time to irrigate is

Available water shown by the example given in

Soil texture: (inches perfoot) ^^^j^ 2. The Starting balance is

SandyToam 1.3 estabhshed after sufficient rainfall

Loam lllLlllllll--- 1.8 or irrigation fills the storage capacSiltloam 2.2 ity of the soil to the 2-foot depth.

Clay loam 1.9 j^ ^^j^i^ 2, corn will be irrigated

Clay 1.8 ^^^^ ^Q percent of the available

Values for daily evapotranspira- water in the 2-foot depth has been

tion losses have been estimated by used. The farm is located between

Van Bavel (27) and are shown in latitude 30° and 34° N.

TABLE 1.—Estimated values of daily évapotranspiration during certain

months and for different latitudes under specified weather conditions

Latitude ^ and month

Between 48° and 40° N. :

April and September.

May and August

June and Julv

Between 40° and 34° N.:

April and September.

May and August

June and July

Between 34° and 30° N.:

April and September

May and August

June and July

Daily évapotranspiration duringDull,

cloudy

weather

Inch

0.06

.07

. 12

.08

. 11

. 14

.09

. 13

. 14

Normal

weather

Inch

0. 09

. 12

. 17

. 11

. 14

. 17

. 13

. 16

.17

Bright,

hot

weather

Inch

0. 13

18

22

14

19

23

, 16

.22

.23

1 The values given in (27) have been expanded by Van Bavel to include the latitudes shown.

TABLE 2.—Example showing how to use weather records to estimate time to

irrigate corn in a sandy loamfield located between latitude S0° and 34"^ N.

[Crop to be irrigated when 50 percent of the available water in the 2-foot depth has been usedl

Date

Evapotranspiration

Rainfall

Irrigation

Balance

Inch

June 2_

June 3-

June 4_

June 5_

June 6_

June 7_

June 8_

June 9_

Inches

2.23

Inches

0.23

.23

. 17

.23

. 14

. 23

. 13

1. 50

Inches

2.00

1.77

1. 54

1.37

1. 14

1. 13

.90

2.00
IRRIGATION OF CORN 9

On June 2 the rainfall of 2.23

inches was sufficient to fill the 2-

foot soil storage capacity with 2.00

inches of water. Since the effective root-zone depth is 2 feet and

2.00 inches of water are required

to fill the storage capacity of sandy

loam to this depth, the established

balance is 2.00 inches, which was

entered in the balance column

(table 2). Evapotranspiration

values for June 3 through 8 were

taken from table 1. Time to irrigate was when 50 percent of the

available water in the 2-foot depth

was used. On June 9, 1.50 inches

of water was appHed, and the

balance was once more up to 2.00

inches. Excesses above a 2.00-

inch balance are discarded, since

they are considered lost by drainage

into the subsoil or by runoff. Day

by day, the record is kept in this

manner. A new balance is obtained

each day by adding rainfall and

water applied by irrigation and

subtracting the évapotranspiration

values from the balance.

Growth of corn will continue

after the base amount of moisture

is gone, but not without some reduction in rate. Some corn roots will

withdraw moisture from below the

second, third, or even fourth foot of

soil depth after the upper reserves

are exhausted, but growth will be

slower than if moisture is adequate.

Decrease in growth will be accompanied by losses in yield, if prolonged moisture stress and wilting

occurs during the tasseling to early

dent stage (32).

IRRIGATION METHODS

Slope, intake rate, and other

characteristics of the soil determine

the method of irrigation to be used.

Furrow methods are used on land

with slopes of less than 0.5 percent

or almost level. Sprinklers are

used on deep sandy soils of high

intake rate, on rolling land, on

steep slopes, or where grading will

remove too much fertile soil in

cutting down ridges and knolls.

Sprinkler Method

The sprinkler system should be

designed by a competent technician.

The layout should be planned to fit

all fields that are to be irrigated.

Sprinklers should be selected that

will apply water at the proper rate

and that give proper coverage.

Sprinkler irrigation of corn requires

risers up to 10 to 12 feet in length

that must be well supported.

The water source, its location

with respect to the field, and the

nature and size of the fields to be

irrigated principally determine the

layout of the system. Since power

consumed by sprinkling water under

pressure increases both with height

and distance from source to the

sprinklers, the fields to be irrigated

should be as close as possible to the

water supply.

The sizes of pipe should be chosen

for both economy and good pressure

distribution. Cost increases with

pipe diameter. Main line and lateral line sizes should be selected

with consideration for adequate

distribution with greatest economy.

Help in planning an irrigation

system may be obtained from the

Soil Conservation Service technician or the Extension Service engineer in the area concerned. The

system should be large enough to

get over the area to be irrigated as

quickly and as often as necessary

to prevent serious drought damage.

The number of hours needed to

operate the system economically

and conveniently should be considered. A smaller system can be

used if it is operated 16 to 20 hours

rather than the regular 8-hour day.
10 AGR. HAXDBOOK 14 0, U. S. DEPT. OF AGRICULTURE

Distribution with sprinkling during

windy periods is poor. Strong

winds often occur at some locations

during certain hours of the day;

if possible, operation of sprinklers

at such times should be avoided.

Also, because of lower evaporation

losses due to lower temperatures

and higher humidity, irrigation at

night may be profitable if the gain

in efficiency is not offset by higher

labor costs.

Moving sprinkler irrigation pipe

in tall corn, without special mechanical aids, is difficult and expensive. Kummer (16) has tested

the feasibility of leaving alleys in

the corn for transporting and laying

sprinkler lines. This means a sacrifice in land planted to crops to

reduce labor costs.

Furrow Method

Furrow irrigation should not be

used on slopes of more than 0.5

percent unless rows are laid on the

contour (7, 21). Slopes of more

than 2 percent should be considered

too steep for furrow irrigation even

when rows are graded to 0.5 percent

on the contour. More nearly level

land is easier to grade for furrow

irrigation. Smoothing out irregularities is desirable, but land that

requires extensive deep cuts to make

it uniform should be irrigated by

the sprinkling system. Land leveling is limited to soils that are deep

enough that the needed cuts and

fills do not permanently reduce

productivity. Also, in humid areas,

it is generally considered too costly

to move more than 600 cubic yards

of earth per acre.

The furrow method is best

adapted to nearly level land (less

than 0.5-percent slope), where little

grading is needed, or to deep

fertile soils where considerable soil

can be cut from higher ridges and

knolls without reducing productivity (7). Water for this method

is distributed to the field by gravity

from canals and ditches or by a

system of pipelines.

The cost for equipment for pipelines is greater than for ditches for

transportation of water to the field.

Unless pipes are buried, they are

difficult to cross or go around and

bring inconvenience to the operation of farm machinery. Pipelines

must be assembled where needed,

and, unless extra pipe is bought,

lines must be moved as progress is

made across a field or when moved

to new fields. During long periods

of disuse the pipes should be disassembled and stored. Buried pipelines are expensive, but the initial

cost may be more than offset by

the durability and convenience of

such system if it is properly planned

and laid out. It is best to use

gated pipe for distribution to the

furrows (fig. 4). With a wellplanned pipeline s^^stem on land

well adapted to this method, good

distribution of water can be

achieved.

Ditches may be used to transport

water to the field and distribute it

to the furrows. Initial equipment

costs are less, but extra land is

needed. Ditches entail inconvenience in crossing wdth farm machinery and equipment. Also, with

sandy or gravelly soils, water loss

in transportation to the fields will

be great unless the canals and

ditches are lined with cement,

plastic, or other materials. Seepage

and transpiration losses increase as

ditches become clogged with soil

materials and weeds. Ditches must

be maintained and kept free of

debris. The best method of distribution from field ditches to

furrows is by means of siphon hoses.

By adjusting the size and number

of siphons to each furrow the rate

of flow and distribution can be

controlled. Where it is desirable

to irrigate in furrows graded on the
IRRIGATION OF CORN 11

Figure 4.—Use of sated pipe for furrow irrigation of corn: A, More rapid flow is used until

water is nearly to the end of the furrow,- B, then the rate is cut back to a slow rate until the

desired amount is applied.
12 AGR. HANDBOOK 14 0, U. S. DEPT. OF AGRICULTURE

contour, the direction of slope

should be chosen to give convenient

access to the supply ditch.

Disposal of drainage from the

lower end of the furrows should be

considered. Also, ponding of water

in the furrows from rainfall and

irrigation often causes damage to

the crop. A furrow grade of at

least 0.05 percent with the direction of flow is needed to assure

surface drainage (21).

AMOUNT AND RATE TO USE

Sprinkler Application

The application rate of water by

sprinklers can be accurately controlled. The importance of applying water at a rate slow enough for

the soil to absorb practically all as

it falls cannot be overemphasized.

When the water intake rate of soil

is exceeded, the surface soil may

be puddled, which reduces the intake rate and seals the soil surface;

runoff occurs; aeration is impaired;

and evaporation from the soil

surface is increased.

Different soil types have varying

capacities for storage of absorbed

water. When a soil has been thoroughly wetted and excess water

has drained, the soil water storage

capacity is completely filled. Corn

will exhaust water to depths greater

than 2 feet, but irrigations will be

made to recharge the soil capacity

to the 2-foot depth, since most of

the roots are in this zone.

The Soil Conservation Service

Irrigation Guide (26) for each

State is an excellent source of technical information for developing

and operating the irrigation system.

The South Carolina guide, for

example, describes the soil profiles,

gives application rates derived from

experimental intake rates, and provides data of moisture to be replaced and amount to be applied,

based on the efficiency of the sprinkler system. Data on root zone

depths and peak use of moisture

by most plants that may be irrigated are shown. Application rates

can be increased to some extent

under mulch tillage and on some

very sandy soils on 1- to 2-percent

slopes. However, extreme caution

should be exercised in ^ selecting

other rates of application than

those given.

Furrow Application

The application rate of water in

furrow irrigation is determined by

row spacing, row length, and

amount of water turned into each

furrow (7, 21). Soils with less than

0.5-percent slope, which soak up

ji to 1 inch of water per hour, are

best suited to furrow application.

The length of the furrow that can

be irrigated from each field ditch

or pipe setting will vary with

different slopes and different soils.

Usually water should be delivered

to the lower end of the run in about

one-fourth of the time necessary to

deliver the full amount needed.

When the water nears the lower

end, the rate of flow should be

reduced to avoid excessive waste.

If gated pipe or siphons are used,

the flow rate can be controlled

easily. If openings to the furrows

are made in field ditches and

delivery laterals, adjustable weirs

formed with stakes or other restrictive devices must be placed at the

furrow intake end to control the

amount of water. These need to

be checked and adjusted frequently

to avoid washouts and erosion

damage.
IRRIGATION OF CORN 13

GENERAL RECOMMENDATIONS

Plant a corn variety that is well If there is no rain, corn will use

adapted to the specific location and about 50 percent of the total availaim at about 15,000 plants per acre, able water in silt loam bottom land

Fertilize with 100 to 150 pounds in 12 to 15 days; in soils of the

of nitrogen per acre. Apply phos- Piedmont in 8 to 10 days; and in

phoric acid and potash according sandy soil in the Coastal Plain in

to soil tests or at the rate recom- 4 to 5 days. To irrigate when

mended by the State agricultural about 50 percent of available soil

experiment station; usually about water remains: (1) Examine corn

100 pounds per acre of each. Main- for wilting about 10 a. m. and

tain a pH value of 6.0 to 6.5. check soil at plow depth for

Cultivate shallow to control ''balling^^ test (p. 6); and (2) use

^ggjg weather data balance method of

Irrigate throughout growing sea- ^^^ÏSble''^ ^^'''' **" ' ^''**'' '^

son if water sup1% is plentiful and P^¿^¿ ^^^^ ¿^1 application of

time IS not limited, or irrigate by needed water

the tassehng to early dent stage Apply enough water to refill

method if water and time are storage capacity of soil to about

limited. 2 feet deep.

LITERATURE CITED

(1) BROWN, D. A., and BENEDICT, R. H.

1953. INCREASING CORN YIELDS THROUGH SUPPLEMENTAL IRRIGATION. Ark,

Farm Res. 2 (4): [3], illus.

(2) and BENEDICT, R. H,

1954. INCREASING CROP YIELDS THROUGH IRRIGATION. Ark. Farm Res. 3 (4):

[4], illus.

(3) and BENEDICT, R. H.

1956. SUPPLEMENTAL IRRIGATION HELPS MAINTAIN CORN YIELDS. Ark. Farm

Res. 5 (4) : 4, illus.

(4) CAMPBELL, J. A.

1953. IRRIGATION FOR VEGETABLE CROPS. Miss. AgT. Expt. Sta. Cir. 182, 8 pp.

(5) DECKER, W. L.

1952. MONTHLY PRECIPITATION IN MISSOURI: CLIMATIC ATLAS OF MISSOURI

NO. 1. Mo. Agr. Expt. Sta. Bui. 572, 80 pp., illus.

(6) DicKERsoN, R. L., EDWARDS, F. E., JORDAN, H. V., and others.

1952. IRRIGATION EXPERIMENTS ON CROPS AND PASTURES. Miss. Farm Res.

15 (4): 4-5, illus.

(7) GRISSOM, P., and RANEY, W. A.

1953. SELECTION AND USE OF IRRIGATION EQUIPMENT FOR MISSISSIPPI. MisS

Agr. Expt. Sta. Cir. 181, 14 pp., illus.

(8) EDWARDS, F. E., KIMBROUGH, E. A., DICKERSON, R., and others.

1951. EFFECTS OF IRRIGATION ON CORN AND PASTURE STUDIED. MiSS. Farm

Res. 14 (5): 1, 7, illus.

(9) ENNIS, L., JR.

1955. SUMMARY OF IRRIGATION EXPERIMENTS IN OTHER SOUTHEASTERN STATES.

Ala. Agr. Expt. Sta. Water Resources and Sup. Irria;. Workshop

Proc, pp. 19-22, ^ B h^

(10) GINGRICH, J. R., and RUSSELL, M. B.

1956. EFFECT OF SOIL MOISTURE TENSION AND OXYGEN CONCENTRATION ON

THE GROWTH OF CORN ROOTS, Agron. Jour. 48: 517-520, illus.

(11) GRISSOM, P. H., RANEY, W. A., DICKERSON, R., and others.

1953. CROP RESPONSE TO IRRIGATION IN MISSISSIPPI. Miss. Agr. Expt. Sta,

Cir. 180, 12 pp.

(12) RANEY, W. A., and HOGG, P.

1955. CROP RESPONSE TO IRRIGATION IN MISSISSIPPI DELTA. Míss. Farm Res

18 (5): 1, 2-5, 8, illus.
14 AGR. HANDBOOK 140, U. S. DEPT. OF AGRICULTURE

(13) GRISSOM, P. H., RANEY, W. A., and HOGG, P.

1955 CROP RESPONSE TO IRRIGATION IN THE YAZOO-MISSISSIPPI DELTA. MlSS.

Agr. Expt. Sta. Bui. 531, 24 pp.

(14) HuBER, L. L.

1955 PENNSYLVANIA CORN PERFORMANCE STUDIES: DOUBLE CROSS TESTS

1954. Pa. Agr. Expt. Sta. Prog. Rpt. 137, 12 pp., illus.

(15) JAMISON, V. C, and KROTH, E. M.

1958. AVAILABLE MOISTURE STORAGE CAPACITY (TF SOILS IN RELATION TO SOIL

TEXTURE AND ORGANIC MATTER CONTENT. Soil Sci. SoC. Amer. PrOC.

22 (3): 189-192.

(16) KUMMER, F. A.

1955. SUMMARY OF RESEARCH ON IRRIGATION OF ROW CROPS IN ALABAMA.

Ala. Agr. Expt. Sta. Water Resources and Sup. Irrig. Workshop

Proc, pp. 18-19.

(17) LUND, C. M., LAW, W. P., and BEALE, O. W.

1955. SPRINKLER IRRIGATION OF FIELD CORN. S. C. Agr. Expt. Sta. Bui. 421,

34 pp., illus.

as) MURPHY, B. C.

1954 IRRIGATION \ND OTHER CULTURAL STUDIES WITH SWEET CORN, iviiss.

Agr. Expt. Sta. Inform. Sheet 494, 1 p.

1956^ IRRIGATION MADE THE DIFFERENCE. N. Y. State Á'^X-^^Expt. Sta. Farm

Res. 22 (2) : 6, illus.

(20) PicTON, W. L.

1956 SUMMARY INFORMATION ON WATER USE IN THE UNITED STATES, 1900-1975.

U. S. Dept. Com. Business Serv. Bui. 136, 6 pp., illus. [Processed.]

(21) QuACKENBUSH, T. H., RENFRO, G. M., BEAUCHAMP, K, H., and others.

1957 CONSERVATION IRRIGATION IN HUMID AREAS. U. S. Dept. Agr., Agr.

Handb. 107, 52 pp., illus.

(22) RICHARDSON, J. B., and BEALE, O W. T. ^ CJ+ A -D ^ r:n O^ on

1947. IRRIGATION OF CORN. S. C. Agr. Expt. Sta. Ann. Rpt. 59: 24-29,

illus. ^ -n. XT

(23) SCHWAB, G. O., SHRADER, W. D., NIXON, P. R., and SHAW, R. H.

1958. RESEARCH ON IRRIGATION OF CORN AND SOYBEANS AT CONESVILLE AND

ANKENY, IOWA, 1951-1955. lowa Agr. Expt. sta. Res. Bui. 458, pp.

245-259, illus.

(24) SMITH, D. D. ^ ^^ r^

1954 FERTILITY INCREASES EFFICIENCY OF SOIL MOISTURE. Better Crops

With Plant Food 38 (6) : 11-12, 39, illus.

(25) SNIDER, R. G. T /in I«^ ITO

1957. YOUR SHARE IN TOMORROW'S WATER. Agrou. Jour. 49: 167-17^.

(26) SOIL CONSERVATION SERVICE. r . . i x •

TENTATIVE SPRINKLER IRRIGATION GUIDE FOR [certam areas and certain

States]. [Processed.]

(27) VAN BAVEL, C. H. M.

1956. ESTIMATING SOIL MOISTURE CONDITIONS AND TIME FOR IRRIGATION

WITH THE EVAPOTRANSPIRATION METHOD. U. S. Dept. Agr. ARS41-11, 16 pp., illus. [Processed.] ^

(28) FORREST, L. A., and PEELE, T. C. a ^ A r^ 4. a., -D i

1957. AGRICULTURAL DROUGHT IN SOUTH CAROLINA, b. C. Agr. Expt. bta. Bui.

447, 36 pp., illus.

(29) and LILLARD, J. H. XT X r? 4. 04. n. . -R„I

1957. AGRICULTURAL DROUGHT IN VIRGINIA. Va. Agr. Expt. bta. iech. I5ul.

128, 38 pp., illus.

(30) _ and VERLINDEN, F. J. TVT ^ A T:^ 4- 0+

1956 AGRICULTURAL DROUGHT IN NORTH CAROLINA. N. C. Agr. Expt. bta.

Tech. Bui. 122, 60 pp., illus. _

(31) United States Weather Bureau, Hydrologie Services Division.

1955 RAINFALL INTENSITY-DURATION FREQUENCY CURVES FOR SELECTED

STATIONS IN THE UNITED STATES, ALASKA, HAWAIIAN ISLANDS AND

PUERTO RICO. U. S. Dept. Com. Weather Bur. Tech. Paper 25,

53 pp., illus.

i'\'?\ W^HITT D IVI -n

' 1954 EFFECTS OF SUPPLEMENTAL WATER ON FIELD CROPS. Mo. Agr. Expt.

Sta. Bui. 616, 8 pp., illus.

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