• TABLE OF CONTENTS
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 Copyright
 Front Cover
 Table of Contents
 Introduction
 Growth stages
 Production
 Harvesting
 Measuring
 Key management practices
 Conversion chart
 Back Cover






Group Title: Florida Cooperative Extension Service circular 486
Title: Irrigated corn production
CITATION PAGE IMAGE ZOOMABLE PAGE TEXT
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00049273/00001
 Material Information
Title: Irrigated corn production
Series Title: Circular Florida Cooperative Extension Service
Physical Description: 20 p. : ill. ; 28 cm.
Language: English
Creator: Wright, D. L ( David L )
Rhoads, Frederick Milton
Stanley, R. L
Publisher: Florida Agricultural Experiment Stations in cooperation with the Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
Place of Publication: Gainesville
Publication Date: 1980?
 Subjects
Subject: Corn -- Irrigation   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by D.L. Wright, F.M. Rhoads, and R.L. Stanley.
General Note: Cover title.
Funding: Florida Historical Agriculture and Rural Life
 Record Information
Bibliographic ID: UF00049273
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida
Resource Identifier: oclc - 08853101

Table of Contents
    Copyright
        Copyright
    Front Cover
        Front Cover
    Table of Contents
        Page 1
    Introduction
        Page 2
    Growth stages
        Page 2
    Production
        Page 3
        Site selection
            Page 4
        Soil texture
            Page 4
        Date of planting
            Page 5
            Page 6
        Plant population
            Page 7
        Fertilization
            Page 7
            Page 8
            Page 9
            Page 10
        Secondary and micronutrients
            Page 11
        Tillage
            Page 11
        Weed and pest control
            Page 12
        Rotation
            Page 13
        Irrigation and water scheduling
            Page 13
            Page 14
            Page 15
    Harvesting
        Page 16
    Measuring
        Page 16
        Page 17
        Page 18
    Key management practices
        Page 19
    Conversion chart
        Page 20
    Back Cover
        Back Cover
Full Text





HISTORIC NOTE


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
(EDIS)

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida




Circular 486


IRRIGATED CORN
PRODUCTION

































CONTENTS


Page Number
I. Introduction
II. Growth Stages
III. Production ............ .. .......... 3
1. Site Selection ....................... 4
2. Soil Texture ........................ 4
3. Hybrid Selection .................... 4
4. Date of Planting .................... 5
5. Plant Population .................... 7
6. Fertilization ........................ 7


7. Secondary and Micronutrients ..... 11
8. Tillage ........................... 11
9. Weed and Pest Control ...............12
10. Rotation ........................... 13
11. Irrigation and Water Scheduling ...... 13
Harvesting ........................... 16
M easuring ........................... 16
Key Management Practices ............. 19
Conversion Chart ........................ 20










INTRODUCTION
Drought conditions and the uncertainty of adequate
rainfall in the grainfilling period of corn has resulted
in the adoption of irrigation as a practice by many
growers who grow corn on sandy Coastal Plain soils.
Research from the past few years has shown that high
yields of corn can be grown on these soils where water
and nutrients are managed to meet plant needs.
Many of the risks of growing corn are reduced when
irrigation is used. However, a higher level of manage-
ment is needed with irrigation, and fertility, plant
population, weed control and other factors may be dif-
ferent from those used with non-irrigated corn. The
purpose of this publication is to provide information to
growers that have little information on aspects of
growing irrigated corn and the value of these practices
when deciding to use irrigation.

Irrigated Corn Production Guide
Growth Stages
Planting-depth of corn influences the length of time
from planting to emergence. Deep-planted seedlings
require a longer time to penetrate the soil surface than
seedlings that are planted shallow. Cool temperatures
also slow growth and development further. Therefore,
early plantings should be shallow. Planting depth de-
termines the depth at which the primary roots radiclee
and seminal roots) develop, but does not influence the
depth at which the nodal (permanent) roots develop.
Fertilizer placed in a band to the side and slightly
below the seed may make contact with the primary
roots before the plant emerges. This stimulates early
growth on soils not heavily fertilized, or that have a soil
test level of medium or less. Too much fertilizer near
the seed can result in salt injury to the plant, but close
placement of fertilizer to young plants will enhance
uptake since the primary roots radiclee) are the main
uptake route. Roots are not attracted to a fertilizer
band, so the fertilizer must be placed near the roots or
the roots must grow into the band.
Corn is one of the most energy efficient major crops
grown. The rate of development is directly related to
temperature, so the length of time between growth
stages varies as the temperature varies. Increased day
lengths in the early development of corn results in
more leaves per plant, which results in taller plants
that are more likely to lodge; therefore, long days in the
Northern United States or late planting in the South-
east may result in taller plants. At the four leaf stage
of development or about 2 weeks after emergence, the
tassel is initiated in the tip of the stem which is still
below the soil surface. A frost at this time may damage
exposed leaves but will do no harm to the growing


point below the soil surface, and results in little if any
yield reduction.
Mid-February plantings of corn receive very little
damage from cold and often produce higher yields than
late-planted corn because they escape severe insect
and weed problems. They also have a more favor-
able environment during pollen shed and ear filling
periods.
If flooding occurs while the growing point of the
plant is below the soil surface, corn may be killed in a
few days, especially if high temperatures are preva-
lent. At 4 weeks after emergence, corn is near the
eighth fully expanded leaf stage and the growing tip
moves 2 to 3 inches above the soil surface. Flooding is
not as detrimental to the crop when the growing point
stays above the water.
Five weeks after emergence, or when the tenth leaf
has fully emerged, moisture and nutrient deficiencies
markedly influence the growth and development of the
ears. After this period, corn should not be cultivated or
tilled because of damage that may be done to the exten-
sive root system of the plant. Broadcast applications of
nitrogen are effective at this time due to the size of the
root system.
Potential size of the harvested ear is related to the
time interval from full emergence of the twelfth leaf
until silking. The twelfth leaf is usually fully emerged
about 6 weeks after seedling emergence. Early-ma-
turing hybrids progress through this period faster than
later-maturing varieties and usually have smaller ears.
As a result, they should be planted in higher plant pop-
ulations than full season varieties to obtain maximum
yields and for weed control.
Moisture stress or nutrient deficiency at the six-
teenth fully emerged leaf stage (about 9 weeks after
planting) delays silking more than tassel emergence
and pollen shedding. These stresses tend to intensify
from the top to the bottom of the plant. Therefore, most
of the pollen may be shed before the silks emerge, or
the silk may dry up before pollination.
Silks elongate until they are pollinated. This occurs
when leaves and tassel have fully expanded at about 9
weeks after emergence. Hot, dry weather may result
in poor pollination and seed set. Potassium uptake
during this period is almost complete while nitrogen
and phosphorus uptake is rapid. At this stage, the re-
sults of the leaf analysis would be highly correlated to
the grain yield and expected yield responses from fer-
tilizer applications.
The period from silking to 3 weeks after silking is
the most critical for adequate water. Corn should be ir-
rigated to maintain adequate moisture during this pe-
riod for high grain yields.
Two weeks after silking, the cob, husks, and shank
develop fully. A rapid increase in dry weight occurs










INTRODUCTION
Drought conditions and the uncertainty of adequate
rainfall in the grainfilling period of corn has resulted
in the adoption of irrigation as a practice by many
growers who grow corn on sandy Coastal Plain soils.
Research from the past few years has shown that high
yields of corn can be grown on these soils where water
and nutrients are managed to meet plant needs.
Many of the risks of growing corn are reduced when
irrigation is used. However, a higher level of manage-
ment is needed with irrigation, and fertility, plant
population, weed control and other factors may be dif-
ferent from those used with non-irrigated corn. The
purpose of this publication is to provide information to
growers that have little information on aspects of
growing irrigated corn and the value of these practices
when deciding to use irrigation.

Irrigated Corn Production Guide
Growth Stages
Planting-depth of corn influences the length of time
from planting to emergence. Deep-planted seedlings
require a longer time to penetrate the soil surface than
seedlings that are planted shallow. Cool temperatures
also slow growth and development further. Therefore,
early plantings should be shallow. Planting depth de-
termines the depth at which the primary roots radiclee
and seminal roots) develop, but does not influence the
depth at which the nodal (permanent) roots develop.
Fertilizer placed in a band to the side and slightly
below the seed may make contact with the primary
roots before the plant emerges. This stimulates early
growth on soils not heavily fertilized, or that have a soil
test level of medium or less. Too much fertilizer near
the seed can result in salt injury to the plant, but close
placement of fertilizer to young plants will enhance
uptake since the primary roots radiclee) are the main
uptake route. Roots are not attracted to a fertilizer
band, so the fertilizer must be placed near the roots or
the roots must grow into the band.
Corn is one of the most energy efficient major crops
grown. The rate of development is directly related to
temperature, so the length of time between growth
stages varies as the temperature varies. Increased day
lengths in the early development of corn results in
more leaves per plant, which results in taller plants
that are more likely to lodge; therefore, long days in the
Northern United States or late planting in the South-
east may result in taller plants. At the four leaf stage
of development or about 2 weeks after emergence, the
tassel is initiated in the tip of the stem which is still
below the soil surface. A frost at this time may damage
exposed leaves but will do no harm to the growing


point below the soil surface, and results in little if any
yield reduction.
Mid-February plantings of corn receive very little
damage from cold and often produce higher yields than
late-planted corn because they escape severe insect
and weed problems. They also have a more favor-
able environment during pollen shed and ear filling
periods.
If flooding occurs while the growing point of the
plant is below the soil surface, corn may be killed in a
few days, especially if high temperatures are preva-
lent. At 4 weeks after emergence, corn is near the
eighth fully expanded leaf stage and the growing tip
moves 2 to 3 inches above the soil surface. Flooding is
not as detrimental to the crop when the growing point
stays above the water.
Five weeks after emergence, or when the tenth leaf
has fully emerged, moisture and nutrient deficiencies
markedly influence the growth and development of the
ears. After this period, corn should not be cultivated or
tilled because of damage that may be done to the exten-
sive root system of the plant. Broadcast applications of
nitrogen are effective at this time due to the size of the
root system.
Potential size of the harvested ear is related to the
time interval from full emergence of the twelfth leaf
until silking. The twelfth leaf is usually fully emerged
about 6 weeks after seedling emergence. Early-ma-
turing hybrids progress through this period faster than
later-maturing varieties and usually have smaller ears.
As a result, they should be planted in higher plant pop-
ulations than full season varieties to obtain maximum
yields and for weed control.
Moisture stress or nutrient deficiency at the six-
teenth fully emerged leaf stage (about 9 weeks after
planting) delays silking more than tassel emergence
and pollen shedding. These stresses tend to intensify
from the top to the bottom of the plant. Therefore, most
of the pollen may be shed before the silks emerge, or
the silk may dry up before pollination.
Silks elongate until they are pollinated. This occurs
when leaves and tassel have fully expanded at about 9
weeks after emergence. Hot, dry weather may result
in poor pollination and seed set. Potassium uptake
during this period is almost complete while nitrogen
and phosphorus uptake is rapid. At this stage, the re-
sults of the leaf analysis would be highly correlated to
the grain yield and expected yield responses from fer-
tilizer applications.
The period from silking to 3 weeks after silking is
the most critical for adequate water. Corn should be ir-
rigated to maintain adequate moisture during this pe-
riod for high grain yields.
Two weeks after silking, the cob, husks, and shank
develop fully. A rapid increase in dry weight occurs









and starch begins to be stored in the endosperm. Ni-
trogen and phosphorus are taken up rapidly and other
parts of the stem begin giving up nitrogen and phos-
phorus to the developing grain. The soluble sugars
stored in the stalk, ear shanks, and leaf sheath are
translocated to the grain as soon as the kernels begin
to develop, and continues until the dent stage.
In the late dent stage or when corn dries to around
30 to 35%, a black layer is formed at the base of the
kernel, and it is physiologically mature. It should be
harvested at this time and dried to avoid further insect
and disease damage, and to prevent sprouting of ker-
nels and lodging of plants due to wind or rain.

Production
Corn yields are highly correlated with water hold-
ing capacity of Coastal Plain Soils. Common droughts
of three or more weeks during the growing season sub-


Table 1. Estimated costs and returns for one
Hewitt, Quincy)


ject row crops to moisture stress almost yearly. There-
fore, in Florida where irrigation water is not available,
corn can not be profitably grown on a yearly basis.
Nationwide, the average corn yield per acre is near
100 bushels. Florida's average yield for 1979 was 55
bushels, 58 for 1978, 35 for 1977 and 60 in 1976. Good
management with irrigation has been economical in
Florida in good years and insures against losses in
poor crop years. Table 1 shows costs and returns from
irrigated versus non-irrigated corn. Irrigated corn
produced 165 bushels per acre compared to 75 bushels
per acre without irrigation.
Corn without irrigation is often grown in rotation
with soybeans in the southeast. However, since soy-
beans have shown limited response to irrigation, ex-
cept in emergence and drought conditions, corn is being
grown after corn in fields where irrigation is available.
Many of these fields may also have soybeans grown


acre of corn, North Florida, 1979. (Westberry and


Irrigated Non-Irrigated
Item Unit Price Quant. Value Quant. Value

Revenue bu. .2.75 165 453.75 75 206.25
Variable Costs:
Seed Ib. .85 18 15.30 12 10.20
Fertilizer (5-10-15) cwt. 5.60 8.0 44.80 5.5 30.80
Nitrogen lb. N .24 150 36.00 125 30.00
Lime ton 17.00 .33 5.61 .33 5.61
Insecticide Ib. .78 15 11.70 15 11.70
Herbicide Ib. 3.35 4.0 13.40 4.0 13.40
Tractor (125 hp) hr. 6.19 1.25 7.74 1.25 7.74
Truck, pickup mi. .10 20 2.00 20 2.00
Truck 2-Ton mi. .14 20 2.80 20 2.80
Other machinery hr. 1.48 1.25 6.20 1.25 6.20
Combine hr. 11.50 .6 6.90 .4 4.60
Labor hr. 3.50 2.13 7.45 2.13 7.45
Irrigation costs acre 29.62 1.0 29.12
Interest on above expy .06 189.02 11.34 132.50 7.95
Total Variable Costs 200.36 140.45
Return over variable costs 253. 39 65.80
Fixed Costs
Tractor hr. 7.79 1.25 9.74 1.25 9.74
Truck, pickup mi. .10 20 2.00 20 2.00
Truck, 2-Ton mi. .125 20 2.50 20 2.50
Combine hr. 36.83 .6 22.10 .4 14.73
Other machinery hr. 2.67 1.25 3.34 1.25 3.34
Irrigation acre 54.99 1.0 54.99
Total Fixed Costs 99.67 32.31
Total Costs 295.03 172.76
Returns to land and management 158.72 33.49









after soybeans for several years. Rotation is still needed
and should be planned into the cropping system with
irrigation.

Site Selection
The two main types of irrigation systems in use in
the southeast are the self-propelled or cable tow sys-
tem and the center pivot. The center pivot system is
normally designed to irrigate a larger acreage with
less labor than cable tow systems. Systems are avail-
able to irrigate several hundred acres, but field size
and probability of breakdown should limit most sys-
tems to not more than 200 acres. Small or irregularly-
shaped fields can raise the cost of operation for either
system, and are especially expensive for the center-pi-
vot system. The area selected for an irrigation system
should be free of large ditches, trees, and other obsta-
cles before installation and operation if possible. The
site must also have an adequate source of water. Corn
requires from.4 to 20 inches of irrigated water per sea-
son depending upon rainfall, or about 20 million gal-
lons for 7 inches on a 100 acre field. Additional water
is needed if a second crop is grown on the same field.


Soil Texture
North Florida has many soils classified as either
loamy sands or sandy loams where corn or other row
crops are grown. Table 2 illustrates the available water
per foot depth, land value, and expected yield with and
without irrigation on different soils.
Costs of non-irrigated corn is about $120 less per
acre than with irrigation. However, the best yields on
the best soils without irrigation allow little chance for
profit. Irrigation of sandy soils can produce yields near
those of the best loam soils. However, a higher level of
management and more timely water and fertilizer ap-
plications are necessary for sandy soils. Production


costs are also higher for irrigated as compared to non-
irrigated corn. Irrigation schedules may not permit
watering as needed and, therefore, short periods of
stress may be encountered during hot, dry periods.
Then the sandier soils will suffer more and need to be
irrigated first and more often when soil moisture lev-
els are low.


Hybrid Selection
Selection of high-yielding hybrids under high plant
population and fertility is very important. A list of rec-
ommended field crop varieties is released by the Flor-
ida Extension Service to determine hybrids each year
and other row crop varieties that excel in each area of
the state. It is imperative to choose high-yielding hy-
brids with the following characteristics:
1. Have high seed quality to give good emergence
for late February plantings.
2. Have good stalk strength under high popula-
tions.
3. Have resistance to leaf blight under high humid-
ity.
4. Have few barren stalks.
5. Have a good shuck cover to prevent entry of in-
sects and disease organisms.
6. Have a heavy ear that turns down when not har-
vested immediately after maturity to prevent weath-
ering and sprouting of mature unharvested corn.
7. Mature at a time that fits in with other farming
operations or be a short season variety for multiple
cropping purposes.
Use of early- or full-season corn varieties will de-
pend upon: (1) whether the land is to be double cropped,
(2) the planting date, and (3) if drying facilities are
available. An early-season corn variety matures from
12 to 20 days before a full-season variety (Fig. 1).
Early-season corn is from 3 to 4% lower in moisture at


Table 2. Approximate available water, estimated land value (1979) and corn yields
under good management as related to soil texture.


Land Estimated
Available Value Yield
Soil Water/foot Non- Without With
texture of depth Irrig. Irrig. Irrigation Irrigation
inches bu/acre


Sands
Loamy sands
Sandy loams
Loams
Clay loams


.25- .75
.75-1.25
1.25-1.75
1.75-2.25
2.25-2.75


600
900
1000
1200
1500


450
600
650
900
1000


State average 54 150









after soybeans for several years. Rotation is still needed
and should be planned into the cropping system with
irrigation.

Site Selection
The two main types of irrigation systems in use in
the southeast are the self-propelled or cable tow sys-
tem and the center pivot. The center pivot system is
normally designed to irrigate a larger acreage with
less labor than cable tow systems. Systems are avail-
able to irrigate several hundred acres, but field size
and probability of breakdown should limit most sys-
tems to not more than 200 acres. Small or irregularly-
shaped fields can raise the cost of operation for either
system, and are especially expensive for the center-pi-
vot system. The area selected for an irrigation system
should be free of large ditches, trees, and other obsta-
cles before installation and operation if possible. The
site must also have an adequate source of water. Corn
requires from.4 to 20 inches of irrigated water per sea-
son depending upon rainfall, or about 20 million gal-
lons for 7 inches on a 100 acre field. Additional water
is needed if a second crop is grown on the same field.


Soil Texture
North Florida has many soils classified as either
loamy sands or sandy loams where corn or other row
crops are grown. Table 2 illustrates the available water
per foot depth, land value, and expected yield with and
without irrigation on different soils.
Costs of non-irrigated corn is about $120 less per
acre than with irrigation. However, the best yields on
the best soils without irrigation allow little chance for
profit. Irrigation of sandy soils can produce yields near
those of the best loam soils. However, a higher level of
management and more timely water and fertilizer ap-
plications are necessary for sandy soils. Production


costs are also higher for irrigated as compared to non-
irrigated corn. Irrigation schedules may not permit
watering as needed and, therefore, short periods of
stress may be encountered during hot, dry periods.
Then the sandier soils will suffer more and need to be
irrigated first and more often when soil moisture lev-
els are low.


Hybrid Selection
Selection of high-yielding hybrids under high plant
population and fertility is very important. A list of rec-
ommended field crop varieties is released by the Flor-
ida Extension Service to determine hybrids each year
and other row crop varieties that excel in each area of
the state. It is imperative to choose high-yielding hy-
brids with the following characteristics:
1. Have high seed quality to give good emergence
for late February plantings.
2. Have good stalk strength under high popula-
tions.
3. Have resistance to leaf blight under high humid-
ity.
4. Have few barren stalks.
5. Have a good shuck cover to prevent entry of in-
sects and disease organisms.
6. Have a heavy ear that turns down when not har-
vested immediately after maturity to prevent weath-
ering and sprouting of mature unharvested corn.
7. Mature at a time that fits in with other farming
operations or be a short season variety for multiple
cropping purposes.
Use of early- or full-season corn varieties will de-
pend upon: (1) whether the land is to be double cropped,
(2) the planting date, and (3) if drying facilities are
available. An early-season corn variety matures from
12 to 20 days before a full-season variety (Fig. 1).
Early-season corn is from 3 to 4% lower in moisture at


Table 2. Approximate available water, estimated land value (1979) and corn yields
under good management as related to soil texture.


Land Estimated
Available Value Yield
Soil Water/foot Non- Without With
texture of depth Irrig. Irrig. Irrigation Irrigation
inches bu/acre


Sands
Loamy sands
Sandy loams
Loams
Clay loams


.25- .75
.75-1.25
1.25-1.75
1.75-2.25
2.25-2.75


600
900
1000
1200
1500


450
600
650
900
1000


State average 54 150










harvest than full-season varieties planted on the same
date (Fig. 2). When properly managed, early-season
varieties yield as high as full-season varieties. In-
creased fuel costs for drying high-moisture full-season
corn make the early hybrid more popular to grow, but
a full-season corn can be left in the field longer if a sec-
ond crop is not going to be grown. Where double crop-
ping is planned, an early hybrid frees the land about
two weeks earlier than a late hybrid.
At least 90 percent of each field should be in two or
three well tested hybrids, and the remainder planted
to untried hybrids if desired. To provide a longer pe-
riod of pollination and allow for better ear tip fill, hy-
brids should have 3 or 4 days difference in maturity
date. When using a 4-row plate planter the main or
early hybrid may be used in 3 boxes with the later hy-
brid in the end box. This gives a planting pattern of 6
rows of main hybrid and 2 rows of the other for better
pollination.


Date of Planting
Years-of research data in the southeast and corn belt
states have shown that early planted corn yields higher
than late planted corn. Some possible reasons for this
are:
1. Higher yield potential
2. Shorter plant allowing higher populations
3. Less insect damage
4. Greater fertilizer response
5. Less summer weed competition


Both early and late season varieties show an in-
creased yield with early planting (Fig. 3). However,
plant populations of corn will be lower with early
planting, due to increased seed rotting in cool, wet
soils. Seeding rates should be adjusted upward by 10
to 15% to allow for seedling mortality and should be
increased another 5 to 10% if no-till planting is used
(Fig. 4).
Late planting of early or full season corn varieties
decreases the days to silking, shortens the early filling
period, and results in smaller ears and lower yields.
Seed size has little to do with final yield, but may have
an effect on rate of emergence. With good planting
conditions, small seed are more economical than large
seed and should be considered under high fertilization
and irrigation (Table 3). Table 4 illustrates the differ-
ence in emergence and final yield obtained from the
various seed sizes.
In North Florida, planting can begin in late Febru-
ary as soon as the seedbed is prepared and soil is dry
enough. However, soils are often too wet until after
March 1 to begin planting.


90

8c
n
o 80


4-15 4-25 5-5 5-15 5-25
Planting Date

Fig. 1. Effects of planting date on days from
planting to maturity (Kansas).


25

24
Full-season
23

22

,21

2 20 -




169
------

I 7- -
16--

15--

14 -


4-15 4-25 5-5 5-15
Planting Date
Fig. 2. Effects of planting date on grain mois-
ture (Kansas).









3 Year Averaae 1976-1978


Bu/Acre
140

130-

120

110

100-
90-

80

70


% Emergence
4 YEAR AVERAGE
100 DATE-RATE-VARIETY SUMMARY


90


SAve All Hybrids
' \ ------Short Season Hybrids
\ ........... Full Season Hybrids











I I I ~ I


I I I I I I I I
2-26 3-7 3-17 3-264-6 4-16 4-26 5-7
Fig. 3. Date of planting study (DeKalb).


i I I I I I I
3-7 3-17 3-27 4-6 4-16 4-26 5-6


Fig. 4. Emergence percentage of corn over a
4-year period (DeKalb).


Table 3. Approximate number of acres planted per 50 pound bag at various populations and seed size.


Kernels per Acres Planted per Bag at Recommended Rates
bag 16,00018,000 20,000 22,000 24,000 26,000 30,000 36,000


104,000 6.5 5.8 5.2 4.7 4.3 4.0 3.5 2.9
96,000 6.0 5.3 4.8 4.4 4.0 3.7 3.2 2.7
80,000 5.0 4.4 4.0 3.6 3.3 3.1 2.7 2.2
69,000 4.3 3.8 3.5 3.1 2.9 2.7 2.3 1.9
57,000 3.6 3.2 2.9 2.6 2.4 2.2 1.9 1.6

94,000 5.9 5.2 4.7 4.3 3.9 3.6 3.1 2.6
86,000 5.4 4.8 4.3 3.9 3.6 3.3 2.9 2.4
70,000 4.4 3.9 3.5 3.2 2.9 2.7 2.3 1.9
58,000 3.6 3.2 2.9 2.6 2.4 2.2 1.9 1.6
49,000 3.1 2.7 2.5 2.2 2.0 1.9 1.7 1.3


80









Table 4. Influence of seed size on emergence and yield (DeKalb) 1977.
XL78 XL394 Avq.


%
Emergence
86.7
85.0
94.8


Bu/
Acre
74.4
76.1
87.0


%
Emergence
89.6
88.3
89.0


Bu/
Acre
100.6
89.3
89.6


%
Emergence
87.7
86.6
92.8


Plant Populations
Plant population in the range of 26,000 to 32,000
plants per acre generally give highest yields in 30" to
36" with irrigation. Tables 5 and 6 show yields ob-
tained with various plant populations and row widths.
Best yields were obtained with 18" rows and 35,000
plants per acre (Table 5). At a constant population of
29,000 plants per acre, higher yields were obtained
from 18" rows and 12" drill spacings (Table 6). Most
population trials and farm operations have 30" or 36"
rows to accommodate modern farm equipment. A pop-
ulation of 30,000 plants in 30" rows with ears averag-
ing 0.5 pound would produce about 200 bushels of corn
per acre. General row widths of 36" to 38" will produce
6 to 12 percent less corn than 30" rows. Close row spac-
ing is advisable for short and early maturing hybrids
because it suppresses late germinating weeds. Table 7
provides information on plant spacing in different row
widths necessary to obtain different population levels.


Fertilization
Proper fertilization with irrigation is important for
high yields and irrigation efficiency (Table 8). Timing
and placement of the application is as critical as the
amount. Nitrogen, phosphorus, and potassium are
generally needed in large amounts with calcium, mag-
nesium and sulfur being used by the plant in smaller
amounts. Nutrient removal by the plant from a 200
bushels corn crop is shown in Table 8 below.
Soil tests should be made well in advance of planting
to determine lime and nutrient needs. Application of
phosphorus and potassium just prior to planting is
usually adequate for plant needs throughout the grow-
ing season. Proper fertilization with N, P, and K re-
sults in earlier silking and maturity of corn, and lower
grain moisture content at harvest. Lower grain mois-
ture results in earlier combining and lower drying
costs (Table 9). Lime should be applied 3 to 5 months
in advance of planting to correct the pH to 5.8 to 6.4
(Fig. 5).


Table 5. Effect of plant populations on corn grain yields. (Quincy)

Plants Per Yield Ave. 1973-74
Acre bu/A

19000 132
23000 147
28000 156
29000 171
35000 183
44000 177


Seed
Size
Small
Medium
Large


Bu/
Acre
85.0
85.0
86.6









Table 4. Influence of seed size on emergence and yield (DeKalb) 1977.
XL78 XL394 Avq.


%
Emergence
86.7
85.0
94.8


Bu/
Acre
74.4
76.1
87.0


%
Emergence
89.6
88.3
89.0


Bu/
Acre
100.6
89.3
89.6


%
Emergence
87.7
86.6
92.8


Plant Populations
Plant population in the range of 26,000 to 32,000
plants per acre generally give highest yields in 30" to
36" with irrigation. Tables 5 and 6 show yields ob-
tained with various plant populations and row widths.
Best yields were obtained with 18" rows and 35,000
plants per acre (Table 5). At a constant population of
29,000 plants per acre, higher yields were obtained
from 18" rows and 12" drill spacings (Table 6). Most
population trials and farm operations have 30" or 36"
rows to accommodate modern farm equipment. A pop-
ulation of 30,000 plants in 30" rows with ears averag-
ing 0.5 pound would produce about 200 bushels of corn
per acre. General row widths of 36" to 38" will produce
6 to 12 percent less corn than 30" rows. Close row spac-
ing is advisable for short and early maturing hybrids
because it suppresses late germinating weeds. Table 7
provides information on plant spacing in different row
widths necessary to obtain different population levels.


Fertilization
Proper fertilization with irrigation is important for
high yields and irrigation efficiency (Table 8). Timing
and placement of the application is as critical as the
amount. Nitrogen, phosphorus, and potassium are
generally needed in large amounts with calcium, mag-
nesium and sulfur being used by the plant in smaller
amounts. Nutrient removal by the plant from a 200
bushels corn crop is shown in Table 8 below.
Soil tests should be made well in advance of planting
to determine lime and nutrient needs. Application of
phosphorus and potassium just prior to planting is
usually adequate for plant needs throughout the grow-
ing season. Proper fertilization with N, P, and K re-
sults in earlier silking and maturity of corn, and lower
grain moisture content at harvest. Lower grain mois-
ture results in earlier combining and lower drying
costs (Table 9). Lime should be applied 3 to 5 months
in advance of planting to correct the pH to 5.8 to 6.4
(Fig. 5).


Table 5. Effect of plant populations on corn grain yields. (Quincy)

Plants Per Yield Ave. 1973-74
Acre bu/A

19000 132
23000 147
28000 156
29000 171
35000 183
44000 177


Seed
Size
Small
Medium
Large


Bu/
Acre
85.0
85.0
86.6











Table 6. Effects of row and drill spacing on corn grain yields at a constant population (Quincy).

Row Spacing Drill Spacing Population Yield
(in.) (in.) Plants/A Bu/A

18 12 29000 204
24 9 29000 180
36 6 29000 178


Table 7. Plant population at various row spacings.
Plant Row width (Inches)
Spacing (inches) 20 30 36 38 40


5.5
5.7
6.0
6.2
6.5
6.8
7.0
7.3
7.5
7.8
8.0
8.3
8.5
8.8
9.0
9.3
9.5
10.0
10.3
10.5
10.7
11.0
11.5
12.0
12.5
13.0
13.5
14.0
15.0


56,500
54,500
52,300
50,200
48,100
46,000
44,800
42,900
41,800
39,700
39,200
37,600
36,600
35,600
34,500
33,500
33,000
31,400
30,300
29,800
29,300
28,500
27,200
16,100
25,100
24,000
23,200
22,400
20,900


37,600
36,200
34,800
33,400
32,100
30,700
29,900
28,600
27,900
26,500
26,200
25,100
24,400
23,600
23,000
22,300
22,000
20,900
20,200
19,900
19,500
19,000
18,100
17,400
16,700
16,000
15,500
14,900
13,900


31,400
30,200
29,000
27,900
26,700
25,600
24,900
23,800
32,200
22,100
21,800
20,900
20,300
19,700
19,200
18,600
18,000
17,400
16,800
16,600
16,300
16,000
15,100
14,500
13,900
13,400
12,800
12,200
11,600


29,700
28,600
27,500
26,400
25,300
24,200
23,600
22,600
22,000
20,900
20,600
19,800
19,200
18,700
18,100
17,600
17,400
16,500
16,000
15,700
15,400
15,000
14,200
13,800
13,200
12,700
12,200
11,800
11,000


28,200
27,200
26,100
25,100
24,000
23,000
22,400
21,400
20,900
19,900
19,600
18,800
18,300
17,800
17,300
16,700
16,500
15,700
15,200
14,900
14,600
14,300
13,600
13,100
12,500
12,000
11,600
11,200
10,500











Table 8. Nutrients utilized by grain and
(Potash/Phosphate Institute).


stover of a 200 bushel corn crop


Nutrient Grain Stover Total


N 160 80 240
P205 65 45 110
K20 40 200 240
Ca 3 42 45
Mg 22 33 55
S 19 16 35


"Pop-up" or high nitrogen and phosphorus fertil-
izers generally give a good yield response on relatively
new crop land or when planting in cold soils. Common
"pop-up" fertilizers (18-46-0 and 10-34-0) are usually
banded near the row at planting for immediate up-
take. Where land has been cropped for several years
and the fertility level is high, little response would be
expected from banded "pop-up" fertilizers with the
normal fertility program. Table 10 illustrates the low
nutrient requirements of corn during the first 25 days.
Timing of nitrogen applications is critical for contin-
ued fast growth and results in less leaching losses
since less than 5% of the nitrogen needed for the crop
is used in the first month. More than 90% of ammo-
nium nitrogen can be nitrified during this period at
soil temperatures of 600 (F) or higher. Some potassium
may be lost during the first month, but almost 70% of
the crop needs are met by the second month and defi-
ciences are not often seen when adequate levels of
potash have been applied at planting time. Application
of 240 pounds of nitrogen per acre is adequate for 200


bushel/A corn when applied in split applications us-
ing a 28,000 to 30,000 plant population.
About 80 lbs/A of nitrogen applied in split applica-
tions produced maximum yields for each 12,000 plants
per acre (Fig. 6). With 30" rows and 36,000 plants per
acre, 240 lbs of nitrogen was required for optimum
yields. If an irrigation injection system is not avail-
able, nitrogen should be applied in a minimum of 3 or
4 applications (depending on the soil type and source
of nitrogen used). Nitrogen should be banded near the
row at planting in a solid or liquid form. As much as
60% of a broadcast application of nitrogen may be lost
due to leaching and movement below the shallow root
zone. A second application can be applied as anhy-
drous ammonia when the plants are knee-high, and a
third application can be flown on as urea prior to tas-
seling. Anhydrous ammonia is available to the plants
for about 2 weeks longer than other nitrogen forms
that are water soluble. Anhydrous ammonia is more
effective on corn that is 3 to 5 weeks old than on newly
planted corn, and should be injected under the row if
applied at planting.


Table 9. Fertility effects on moisture and corn maturity. (North Carolina)

Days to Grain
N P K 80% Silk Moisture

0 70 0 91 50.2
0 70 132 84 44.9
160 70 0 80 50.3
160 70 132 77 43.9











Yield
100

90-

80-

70 -


60-

50


pH YIELD CURVE


30 -

20-

10-


1 I I i I I I
pH 4.5 5.0 5.5 6.0 6.5 7.0
Fig. 5. Influence of pH on yield of corn.



Table 10. Nutrients taken up by a 200 bushel/A
corn crop in periods after emergence
(Potash/Phosphate Institute).
Total
Ist 2nd 3rd 4th Last Ibs
25 days 25 days 25 days 25 days 15 days Uptake
Uptake, %
N 8 35 31 20 6 240
P 05 7 29 39 27 8 110
K20 9 44 31 14 2 240


Nitrogen may be banded as ammonium nitrate, urea,
or other water soluble forms at planting. This can then
be followed by equal applications at knee-high, waist-
high and pretassel. Four applications (planting, knee-
high, waist-high and pretassel) usually result in higher
yields than 2 or 3 applications. Nitrogen may be ap-
plied through the irrigation system, by air or by what-
ever method equipment is available for. With irrigation,
some nitrogen may be lost from the sprinkler head to
the ground. However, optimum use may be attained if
nitrogen and micronutrients are applied 6 or more
times through the irrigation system. This would re-
quire very little extra labor, and would minimize
leaching after heavy rainfalls.


Nitrogen applied through an irrigation system is
often a 28% nitrogen solution (ammonium nitrate in
water with either ammonia or urea). Anhydrous am-
monia cannot be applied in this manner because of
precipitation problems and loss of ammonia into the
air. Liquid nitrogen is usually more expensive than
anhydrous ammonia, and if the difference is substan-
tial, an application of anhydrous ammonia may be
practical.
Liquid fertilizers applied with an injection pump
can be metered into the irrigation system at any de-
sired rate. If liquid fertilizers are used, gallons needed
per acre is calculated as follows:
gal/A = lbs of N/A desired
wt/gal x analysis


If 50 pounds of nitrogen per acre is desired and a
28% nitrogen solution weighing 10.6 pounds per gal-
lon is used,
gal/A = 50 lbs N/A = 16.8 gal/A
10.6 x 0.28



Gallons of nitrogen solution needed per hour is de-
termined by multiplying the acres irrigated/hr by the
gallons needed/A. If 1.10 acres are irrigated per hour
then 1.10 x 16.8 gal/A = 18.48 gal/hr to be metered
into the system.
A high level of management is necessary on both ir-
rigated and non-irrigated corn, but a higher level of
management is required for irrigated corn in order to
time both water and nutrient applications to meet
plant needs.


0 40 80 120 160 200 240 280 320 360 400
N-lbs/Acre
Fig. 6. Effects of several N rates on yields of three
(3) populations of corn in 30 inch rows.
(Quincy)









Frequent tests or spot analyses for nutrient defi-
ciencies of corn tissue may detect nutrient stress be-
fore appearance of deficiency signs. Kits are available
from several sources to determine levels of nitrate,
phosphate and potassium in the tissue for immediate
diagnosis and correction of a nutrient deficiency. Un-
der intensive management such tests are important
for conservation of water and nutrients. These tests
should never substitute for soil testing and a good fer-
tility program before the crop is planted.


Secondary and Micronutrients
Calcium, magnesium and sulfur are considered sec-
ondary nutrients. Levels of calcium and magnesium
for good corn growth are usually available when pH is
corrected to 6.0 or higher with dolometic limestone.
Sulfur is easily leached in sandy soils and should be
applied at the rate of 35 pounds per acre annually in
split applications as with nitrogen. Generally half of
the sulfur may be applied preplant with the remainder
applied through the irrigation system with nitrogen.
Increases in yield have been noted for corn when
zinc and boron were applied. A micronutrient mixture
may be applied at planting time to satisfy zinc and
copper needs. A total of 5 pounds of zinc is needed for
good yields. Boron may be applied through the irri-
gation system in 3 to 4 applications at rates of 12 lb per
application for a total of 2 pounds. Boron applied at 2
week intervals from 4 to 10 weeks has given optimum
yield responses.


Tillage
Tillage procedures for irrigated corn are similar to
those for non-irrigated corn. Growers who disc or chisel
as the primary tillage practice for seedbed preparation
often have more late season weeds than those who
plow. However, a good herbicide program may nullify
that problem. Preplant applications of herbicides are
usually incorporated and can be used on fields with
little or no crop residue. Large quantities of residue on
fields require the use ofpre-emergence or post-emerg-
ence herbicide programs. Where trash is encountered
with no-till or chisel tillage practices, seed should be
planted deeper with a seeding rate of 10% higher.
Many Coastal Plains soils have a tillage pan from
about 4 to 14 inches below the soil surface. This zone
physically impedes root penetration and restricts ex-
ploration for nutrients and water. Frequently this zone
contains high amounts of aluminum which can further
restrict roots chemically. Subsoiling these soils has
resulted in yield increases attributable to root pene-
tration below the tillage pan and enhanced uptake of


additional water and nutrients. Root resistance from
tillage pans may be twice as high on a relative scale
for non-subsoiled as compared to in-row subsoiled fields
at 8 to 12 inches below the surface (Fig. 7). Fields
where corn was harvested in late June and cut with a
disc harrow had more resistance in the subsoiled row
on November 15 than on June 10, but less than the
non-subsoiled rows (Fig. 8). However, with both corn
and soybeans, no yield response was noted when rows
were replanted over the previous years subsoiled fur-
row. Soil resistance in the subsoiled furrow was only
slightly less in the spring of the second year than
where it was not subsoiled, indicating that the plow
pan or tillage pan had reformed (Fig. 8). The area was
harrowed before planting the second year. Corn yields
were not significantly different from the non-sub-
soiled plots, indicating that root penetration was a lim-
iting factor. About 19 months after subsoiling, no
difference was detected between penetrometer read-
ings on the subsoiled or non-subsoiled areas indicating
complete reforming of the plow pan (Fig. 8).
It appears that normal tillage operations cause the
tillage pan to reform each year. This means annual in-
row subsoiling to a depth of about 14 inches is neces-
sary where tillage pans are known to occur. One of the
most common mistakes is subsoiling too shallow to
break the plow pan. This results in increased fuel usage
with no increase in crop yield. Coastal Plains soils are
more subject to tillage pan formation than soils of
other regions because of inadequate freezing and thaw-
ing to break up the pan. The 1:1 type clays of the
Coastal Plain do not expand and contract like the 2:1
type clays in other regions to break up tillage pans
upon wetting and drying.
Subsoiling should not be a routine practice without
confirmation of the presence of a plow pan. This can be
checked by pushing a sharpened metal rod through the
soil during a wet season. A plow pan can be detected by
increased resistance from the 4 to 14 inch depths. If a
plow pan is present, then subsoiling may be profitable,
and should be done in-row with no tillage operation oc-
curring between subsoiling and planting. A spider
wheel may be used directly behind the subsoiler to
close the furrow and keep the seed from falling too
deeply to emerge.
Profitable subsoiling in Coastal Plain soils can be
accomplished by the following: (1) Confirm that a till-
age pan exists, (2) subsoil in-row only, (3) use a spider
wheel or similar equipment to cover the subsoil furrow
to prevent deep placement of seeds, (4) subsoil at
planting time, (5) minimize tillage operations be-
tween subsoiling and planting, (6) subsoil annually
where tillage pan exists and (7) subsoil to a sufficient
depth to penetrate through the tillage pan, usually 14
inches or deeper.









Frequent tests or spot analyses for nutrient defi-
ciencies of corn tissue may detect nutrient stress be-
fore appearance of deficiency signs. Kits are available
from several sources to determine levels of nitrate,
phosphate and potassium in the tissue for immediate
diagnosis and correction of a nutrient deficiency. Un-
der intensive management such tests are important
for conservation of water and nutrients. These tests
should never substitute for soil testing and a good fer-
tility program before the crop is planted.


Secondary and Micronutrients
Calcium, magnesium and sulfur are considered sec-
ondary nutrients. Levels of calcium and magnesium
for good corn growth are usually available when pH is
corrected to 6.0 or higher with dolometic limestone.
Sulfur is easily leached in sandy soils and should be
applied at the rate of 35 pounds per acre annually in
split applications as with nitrogen. Generally half of
the sulfur may be applied preplant with the remainder
applied through the irrigation system with nitrogen.
Increases in yield have been noted for corn when
zinc and boron were applied. A micronutrient mixture
may be applied at planting time to satisfy zinc and
copper needs. A total of 5 pounds of zinc is needed for
good yields. Boron may be applied through the irri-
gation system in 3 to 4 applications at rates of 12 lb per
application for a total of 2 pounds. Boron applied at 2
week intervals from 4 to 10 weeks has given optimum
yield responses.


Tillage
Tillage procedures for irrigated corn are similar to
those for non-irrigated corn. Growers who disc or chisel
as the primary tillage practice for seedbed preparation
often have more late season weeds than those who
plow. However, a good herbicide program may nullify
that problem. Preplant applications of herbicides are
usually incorporated and can be used on fields with
little or no crop residue. Large quantities of residue on
fields require the use ofpre-emergence or post-emerg-
ence herbicide programs. Where trash is encountered
with no-till or chisel tillage practices, seed should be
planted deeper with a seeding rate of 10% higher.
Many Coastal Plains soils have a tillage pan from
about 4 to 14 inches below the soil surface. This zone
physically impedes root penetration and restricts ex-
ploration for nutrients and water. Frequently this zone
contains high amounts of aluminum which can further
restrict roots chemically. Subsoiling these soils has
resulted in yield increases attributable to root pene-
tration below the tillage pan and enhanced uptake of


additional water and nutrients. Root resistance from
tillage pans may be twice as high on a relative scale
for non-subsoiled as compared to in-row subsoiled fields
at 8 to 12 inches below the surface (Fig. 7). Fields
where corn was harvested in late June and cut with a
disc harrow had more resistance in the subsoiled row
on November 15 than on June 10, but less than the
non-subsoiled rows (Fig. 8). However, with both corn
and soybeans, no yield response was noted when rows
were replanted over the previous years subsoiled fur-
row. Soil resistance in the subsoiled furrow was only
slightly less in the spring of the second year than
where it was not subsoiled, indicating that the plow
pan or tillage pan had reformed (Fig. 8). The area was
harrowed before planting the second year. Corn yields
were not significantly different from the non-sub-
soiled plots, indicating that root penetration was a lim-
iting factor. About 19 months after subsoiling, no
difference was detected between penetrometer read-
ings on the subsoiled or non-subsoiled areas indicating
complete reforming of the plow pan (Fig. 8).
It appears that normal tillage operations cause the
tillage pan to reform each year. This means annual in-
row subsoiling to a depth of about 14 inches is neces-
sary where tillage pans are known to occur. One of the
most common mistakes is subsoiling too shallow to
break the plow pan. This results in increased fuel usage
with no increase in crop yield. Coastal Plains soils are
more subject to tillage pan formation than soils of
other regions because of inadequate freezing and thaw-
ing to break up the pan. The 1:1 type clays of the
Coastal Plain do not expand and contract like the 2:1
type clays in other regions to break up tillage pans
upon wetting and drying.
Subsoiling should not be a routine practice without
confirmation of the presence of a plow pan. This can be
checked by pushing a sharpened metal rod through the
soil during a wet season. A plow pan can be detected by
increased resistance from the 4 to 14 inch depths. If a
plow pan is present, then subsoiling may be profitable,
and should be done in-row with no tillage operation oc-
curring between subsoiling and planting. A spider
wheel may be used directly behind the subsoiler to
close the furrow and keep the seed from falling too
deeply to emerge.
Profitable subsoiling in Coastal Plain soils can be
accomplished by the following: (1) Confirm that a till-
age pan exists, (2) subsoil in-row only, (3) use a spider
wheel or similar equipment to cover the subsoil furrow
to prevent deep placement of seeds, (4) subsoil at
planting time, (5) minimize tillage operations be-
tween subsoiling and planting, (6) subsoil annually
where tillage pan exists and (7) subsoil to a sufficient
depth to penetrate through the tillage pan, usually 14
inches or deeper.








RESISTANCE
LOW MEDIUM HIGH


Soil resistance in the plow layer for corn
under conventional tillage and with subsoil-
ing. (Quincy).


I I
SUBSOILED IN
^ MMARCH-1976
S NOT SUBSOILEC


I /
- I
- /
/


- /



. APRIL-15-1977


RESISTANCE
LOW MEDIUM HIGH


I I
\ NOT SUBSOILED


K /

- -
SUBSOILED IN\
- MARCH-1976 \









OCT-4-1977
-/
- I



- OCT-4-1977


Fig. 8. Left, dotted line shows resistance in the
plow layer after subsoiling in 1976 and sol-
id line not subsoiled in 1976 or 1977, right,
dotted line shows resistance 19 months af-
ter subsoiling in 1976 and solid line not
subsoiled in 1976 or 1977. (Quincy)


Weed and Pest Control

Weed control is critical during the first 5 to 6 weeks
after planting corn (Table 11). After this, corn is fairly
competitive where high populations are used under ir-
rigation. Mechanical cultivation can be used to kill
weeds, and is very effective when combined with an


MEDIUM HIGH


a
0
o 8
I
a-

12
-J
C)


I I I I
NOT NOT SUBSOILED
I SUBSOILE --

4' SUBSOILED



/ K'
/ /
SSUBSOILED I

7-


I /



- UNE-10-1976 NOV-15-1976

- JUNE-10-1976 NOV-15-1976


10 I


20
Fig. '


application of a herbicide or herbicide-nitrogen solu-
tion. Herbicides should be applied when corn is knee-
high. Early weed control is important for high yields
and ease of harvesting. The "Florida Weed Control
Guide" lists several herbicides which may be tank
mixed alone or with liquid nitrogen for this purpose.
This method may also reduce wind erosion because it
does not loosen soil. Several herbicides have a residual
life of 3 weeks or longer when applied at knee-high or
later. This, together with shading effects from corn
provide good weed control until harvest. Most of the ir-
rigated soils in the Coastal Plains are sandy and low
in organic matter. Therefore, caution must be used
with rates and materials. Sutan butylatee), or Sutan
and Atrazine are the usual preplant herbicides used.
Many herbicides such as Atrazine, Lasso (alachlor),
Dual 6E (metolachlor), Bladex (Cyanazine), Prowl
(pendimethalin), or combinations are used as pre-
emergence. Post-emergence herbicides such as Basa-
gran (bentazon, 2, 4-D Banvel (dicamba), Evik (ame-
tryn), Lorox (linuron), Paraquat and Atrazine or
combinations of these may be used in various weed sit-
uations. The "Florida Weed Control Guide" provides
excellent information on rates and types of weeds con-
trolled, and soils on which the herbicides can be used
safely. Herbicides applied through an irrigation sys-
tem may be determined in the same manner as for liq-
uid fertilizers. Herbicides registered to be used on corn
through the irrigation system may be more effective
than surface applied herbicides due to immediate ac-
tivation of the herbicide when applied to the soil with
water. Herbigation may also be advantageous for time
saving during material application and optimization
of soil-water relationships during planting.
Poor calibration, stopped-up nozzles, and faulty in-
jection equipment may cause phytotoxicity to the corn
crop, and injury to subsequent planted crops. Poor
weed control may be noted in other areas, especially if
sprinklers are not calibrated to put out uniform
amounts across the system.
The irrigation system should be checked out thor-
oughly before herbicide application, since this may
normally be the first time it is used in a season.
Nematodes are a major problem in corn fields that
have been used continuously to grow corn. Figure 9 il-
lustrates that fumigation of these soils can result in in-
creased yields. Rotations and nematicide use can also
help counteract their presence. Major insects that at-
tack corn are armyworms, corn earworms, cutworms,
wire-worms, lesser cornstalk borers, aphids, and white
fringed beetles. No-till farming usually results in in-
creased infestation so a control program is required.
Where corn is grown continuously for several years,
buildup of rootworms is common. Florida's "Insect
Control Guide" gives measures for control of insect


7.


LOW MEDIUM HIGH


0
0
u
SS
8
I-

w 12
o

0o
-
u 16


L








pests. Late planted corn is usually more susceptible to
insect attack than early planted corn.
Increased incidence of leaf blights, smut, and stalk
rot are noted with irrigation because of higher plant
population, humidity, and smaller stalk diameter.
Varietal resistance is the most common measure for
disease control in corn.
Table 11. Effect of weeds on corn yields. (Univ. of.
Illinois).


Weed


weeds allowed to grow
for period indicated


free control 2 weeks 3 weeks 5 weeks

Bu/A 130 120 112 108

Quint/ha 82 75 70 68


Rotation
Corn gives the highest yield response to high levels
of nutrients and scheduled water applications of any
of the row crops. Because of its marked response to ir-
rigation, a grower may continue to grow corn on many
fields to make high. t returns from the system. Corn
-grown in rotation with soybeans or peanuts will often
give 5% or more yield increase and even higher yields
after 4 to 5 years in rotation. This is due to fewer ne-
matode, leaf and root diseases, and insect problems. It
is also due to the recovery of some of the nutrients ap-
plied to the legume crop in rotation. These rotations
will supply some of the needed nitrogen for grain pro-
duction, while lessening the cost of insect and nema-
tode control. However, few growers have large acreages
of peanuts that can be used in rotation with corn. Also,
soybeans show little or no response to irrigation, which
makes continuous corn profitable under irrigation.


220


200
m
S180
_j
w
5: 160
z
' 140
0.


120
I00
looh


LOW MEDIUM HIGH
RELATIVE FERTILIZATION LEVEL
Fig. 9. Fertilization and soil fumigation effects on
yields (Florida).


/
/
/


Irrigation and Water Scheduling
Corn is a shallow rooted plant until it nears tassel-
ing. Highest yields have resulted from frequent irri-
gations of 0.8" per application. Over a 5 year period at
Quincy, yield increases from 35 to 400% have resulted
from the use of irrigation on a variety of soils.
Soils in North Florida and South Georgia hold about
1" of available water in the plow layer. Therefore, rains
or irrigation in amounts exceeding 1" may cause ex-
cess leaching of nutrients or nutrient loss in runoff.
Water requirements for corn, whether from rain or ir-
rigation, are as follows: (1) about 1" of water every 12
days for the first 40 days of growth, (2) about 1" every
5 to 7 days between 40 days and tasseling, and (3) 1"
every 3 to 4 days from tasseling to maturity. Total ir-
rigation or rainfall requirement for corn during the
first 60 days is about 7.7 inches (Table 12). Demand for
water from 60 days to maturity is high, totaling about
13.0", and is especially high and important during the
tasseling and grain filling period. The grain filling pe-
riod is the 3 weeks following tasseling (Fig. 10).
Sandy soils have lower water holding capacities than
loam soils, and require more frequent and lighter ap-
plications of water for highest yields. Applications of
/2 to 3" are adequate. Corn should never be allowed to
wilt since short season corn will mature in about 100
days under some environmental conditions. A drought
period of a few days can significantly lower yields by
shortening plant growth stages.
Table 13 shows results from a field in 1977 where ir-
rigation made a difference of $100 in income over non-
irrigated corn after irrigation costs were accounted for
in a dry year. Since the total cost of installing an irri-
gation system runs from $260 to $300/A, one would
have nearly paid for itself during the 1977 season with
increases above those of non-irrigated corn. Irrigation
equipment is important in producing consistent high
corn yields. A cable tow system may cover many acres
of corn in the first half of the growing season, but not
be adequate to meet water needs of the same acreage
at tasseling and ear filling periods. Therefore, fertil-
izer applications to obtain high corn yields should be
applied only to the corn that can be adequately irri-
gated in the last 40 days. The initial number of acres
irrigated can usually be maintained when using a
center pivot irrigation system.
Scheduling irrigation and nutrient applications ac-
cording to plant needs can minimize nitrogen and po-
tassium losses while supplying needed nutrients
through the irrigation system. This conserves nu-
trients that might otherwise be lost from a single large
application. Timing applications of fertilizer increases
the efficiency of irrigation water and results in in-
creased yields (Table 14). Yields can sometimes be


_








pests. Late planted corn is usually more susceptible to
insect attack than early planted corn.
Increased incidence of leaf blights, smut, and stalk
rot are noted with irrigation because of higher plant
population, humidity, and smaller stalk diameter.
Varietal resistance is the most common measure for
disease control in corn.
Table 11. Effect of weeds on corn yields. (Univ. of.
Illinois).


Weed


weeds allowed to grow
for period indicated


free control 2 weeks 3 weeks 5 weeks

Bu/A 130 120 112 108

Quint/ha 82 75 70 68


Rotation
Corn gives the highest yield response to high levels
of nutrients and scheduled water applications of any
of the row crops. Because of its marked response to ir-
rigation, a grower may continue to grow corn on many
fields to make high. t returns from the system. Corn
-grown in rotation with soybeans or peanuts will often
give 5% or more yield increase and even higher yields
after 4 to 5 years in rotation. This is due to fewer ne-
matode, leaf and root diseases, and insect problems. It
is also due to the recovery of some of the nutrients ap-
plied to the legume crop in rotation. These rotations
will supply some of the needed nitrogen for grain pro-
duction, while lessening the cost of insect and nema-
tode control. However, few growers have large acreages
of peanuts that can be used in rotation with corn. Also,
soybeans show little or no response to irrigation, which
makes continuous corn profitable under irrigation.


220


200
m
S180
_j
w
5: 160
z
' 140
0.


120
I00
looh


LOW MEDIUM HIGH
RELATIVE FERTILIZATION LEVEL
Fig. 9. Fertilization and soil fumigation effects on
yields (Florida).


/
/
/


Irrigation and Water Scheduling
Corn is a shallow rooted plant until it nears tassel-
ing. Highest yields have resulted from frequent irri-
gations of 0.8" per application. Over a 5 year period at
Quincy, yield increases from 35 to 400% have resulted
from the use of irrigation on a variety of soils.
Soils in North Florida and South Georgia hold about
1" of available water in the plow layer. Therefore, rains
or irrigation in amounts exceeding 1" may cause ex-
cess leaching of nutrients or nutrient loss in runoff.
Water requirements for corn, whether from rain or ir-
rigation, are as follows: (1) about 1" of water every 12
days for the first 40 days of growth, (2) about 1" every
5 to 7 days between 40 days and tasseling, and (3) 1"
every 3 to 4 days from tasseling to maturity. Total ir-
rigation or rainfall requirement for corn during the
first 60 days is about 7.7 inches (Table 12). Demand for
water from 60 days to maturity is high, totaling about
13.0", and is especially high and important during the
tasseling and grain filling period. The grain filling pe-
riod is the 3 weeks following tasseling (Fig. 10).
Sandy soils have lower water holding capacities than
loam soils, and require more frequent and lighter ap-
plications of water for highest yields. Applications of
/2 to 3" are adequate. Corn should never be allowed to
wilt since short season corn will mature in about 100
days under some environmental conditions. A drought
period of a few days can significantly lower yields by
shortening plant growth stages.
Table 13 shows results from a field in 1977 where ir-
rigation made a difference of $100 in income over non-
irrigated corn after irrigation costs were accounted for
in a dry year. Since the total cost of installing an irri-
gation system runs from $260 to $300/A, one would
have nearly paid for itself during the 1977 season with
increases above those of non-irrigated corn. Irrigation
equipment is important in producing consistent high
corn yields. A cable tow system may cover many acres
of corn in the first half of the growing season, but not
be adequate to meet water needs of the same acreage
at tasseling and ear filling periods. Therefore, fertil-
izer applications to obtain high corn yields should be
applied only to the corn that can be adequately irri-
gated in the last 40 days. The initial number of acres
irrigated can usually be maintained when using a
center pivot irrigation system.
Scheduling irrigation and nutrient applications ac-
cording to plant needs can minimize nitrogen and po-
tassium losses while supplying needed nutrients
through the irrigation system. This conserves nu-
trients that might otherwise be lost from a single large
application. Timing applications of fertilizer increases
the efficiency of irrigation water and results in in-
creased yields (Table 14). Yields can sometimes be


_









doubled by proper timing, with little leaching of ap-
plied nutrients.
The need for irrigating row crops and especially
corn has been well demonstrated in the past years
where drought conditions occurred for a period of two
or more weeks during the tasseling and silking stage.
In those cases, the results were a complete loss of the
crop or a severe reduction in yield. The irrigation sys-
tem and an adequate water supply constitute a major
capital outlay for any farmer. After the system is in-
stalled, the main investment has been made and the
efficiency of the system will depend to a large extent
on how closely water is supplied to meet plant needs.
For maximum production, water should be managed
in the plow layer. The major portion of a plant root sys-
tem is in the plow layer, so the supply of water to this
area is critical. Overwatering or watering too fre-
quently can leach nutrients out of the root zone which
may slow root growth and create nutrient deficiencies
by reducing uptake. Too little water can also result in
plant stress and slow growth.
Portable models of tensiometers to determine soil
moisture tension are available for a little over $100.00.
They are basically a water filled tube with a porous cup
at the lower end with sealed vacuum gauge on the up-
per end (Fig. 11). It is placed in the soil vertically after
a soil test tube has cored a hole similar to the size of
the tensiometer tube. The porous cup at the end of the
tensiometer should be placed at the depth that soil-
water is to be monitored.
As soil-water is depleted by evaporation, drainage,
and plant uptake, water is pulled from the porous cup
of the tensiometer, creating a vacuum inside which is
shown on the vacuum gauge. As water is added by ir-
rigations, soil suction is reduced and water is drawn
from the soil into the porous cup of the tensiometer and
the reduced vacuum is shown on the vacuum gauge. In
a completely saturated soil the vacuum gauge should
-read zero. One of the most common causes of inaccu-
racy is that the tensiometer is not read often enough so
that the range of the tensiometer is exceeded. This
breaks the vacuum, which starts the reading at zero
again, resulting in false interpretations. Soil-water
tension can be measured in two minutes or less and
read directly from the gauge in centibars of suction.
Other methods involve the installation of soil moisture
blocks than can be maintained in the field throughout
the growing season. With these, moisture readings can
be made in a matter of seconds. These blocks may be
installed at various depths in the soil with wires that
run from the blocks to the surface. The wire can be
clipped to a meter at any time to give a moisture read-
ing. Since this gauge does not operate by vacuum, it is
less likely to give false readings than tensiometers.
If rainfall were adequate and evenly distributed


Table 12. Water use of a short season corn calcu-
lated from rain and irrigation water.
(Quincy)
Days after Inches Total water use
planting per day for period (inches)
0-20 0.05 1.25
20-30 0.07 0.87
30-40 0.12 1.50
40-56 0.16 2.00
50-60 0.17 2.10
60-100 0.26 13.00
0-100 20.75


%
Yield
Reduction
0 r d-


20

30

40

50-


60




EMERGENCE FU POLLI-SOFT
TASSEL NATION DOUGH
Fig. 10. Corn yield as influenced by
stress. (Minnesota)


MATURE

moisture


Table 13. Yield response of corn to irrigation in a
dry year (1977) on a sand with cost
and return figures for sprinkler irrigation.
(Quincy)
Control Irrigation (15cb)
(no irrigation) 45.3 cm (17.8 in)


Yield Kg/ha
bu/A
Increase due
to irrigation bu/A/inch
Irrigation cost $/A-inch
Value of corn at$2.00/bu
Net gain/A inch
Total Cost for 17.8 inch
Net Season gain/17.8 inch


10,035
160


8.3
5.31
16.60/A-inch
11.29
94.52
200.96


i






Table 14. Effect of fertilizer management on water-yield efficiency of corn irrigated with a drip system.
(Quincy)
Conventional Bi-weekly
fertilization Application
kg/ha/cm*
73 150
bu/A/in.
2.96 6.07


*Yield increase per unit of applied water.


V ac uu m G a uge ,,



Fig. 11. A tensiometer consists of an air-tight, water-filled
tube with a porous ceramic tip at the bottom and a
vacuum gauge near the top.The porous ceramic tip
has small pores which allow water to flow in and
out, but which, because of their very small size, pre-
vent air from entering the wetted tip. The unit is in-
stalled with the porous ceramic tip in firm contact
with the soil.

SENSOR CUJ


SOIL LEVEL


SIZE OFUNIT
DEFINES DEPTH
TO ROOT ZONE
1


~1









throughout the growing season, irrigation would be
unnecessary. However, as plants grow and mature,
water requirements often exceed the soil-water avail-
able for plant use and the plants become stressed.
Measuring soil-water throughout the growing season
can help in efficient utilization of irrigation water.
However, the relationship between soil-water content
of individual soils and tensiometer readings must be
known.
Figure 12 shows that% moisture in the soil changes
little from 20 to 100 centibars. Water schedules should
be determined from moisture tension rather than %
moisture in the soil.
The relationship between soil-water content and
tensiometer readings as shown for a loamy fine sand
plow-layer should be well understood. The full point for
this soil is at 5 centibar tensiometer reading or 25%
water content hv volume which is 3 in. per foot of
depth. An 8-in. plow layer would contain 2 in. of water
at the full point. If a tensiometer reading of 20 is se-
lected as the refill point (which corresponds to 15%
water by volume or 1.20 in. in the plowlayer) the amount
required to refill the plowlayer is 2 in. (full point), mi-
nus 1.20 in. (refill point) = 0.80 inches of irrigation
water needed. Frequency of irrigation will be deter-
mined by selection of soil refill point and age of plants.
By reading tensiometers daily the crop manager can
determine when and how much to irrigate from full


- 50

..J
0
o

>-

z 30
z
to
, Z
0
1-,




0
, 10


Fig. 12


and refill points for his particular soil conditions. When
soil reaches the refill point, irrigation should begin
immediately. Crops may be placed under stress condi-
tions for 3 or 4 days waiting for rains. This can reduce
yields, and eliminate yield increases from other good
management practices. Each field should contain at
least three tensiometers located at different positions
with respect to sprinklers.
Table 15 shows irrigation response of corn at three
selected refill points in a loamy fine sandy soil. High-
est yield was produced when the refill point was at a
tensiometer reading of 20. The peak water demand for
corn is about 0.25 in. per day during silking, tasseling
and grain filling periods; therefore, a 3-to-4-day irri-
gation frequency is required for optimum corn produc-
tion with inadequate rainfall.
When using tensiometers to determine the point to
begin irrigating, start early enough that areas covered
at the end of the cycle are not allowed to be above the
20 centibar level or water refill point for a very long
period. If 20 centibars is selected as the point to begin
irrigating, the first area could be watered at 15 centi-
bars. Soil moisture should be maintained by rainfall
and irrigation until plants have reached physiological
maturity and the black layer at the base of the kernel
begins to form. This point is reached at about 35% ker-
nel moisture. A moisture meter may give accurate in-
dication of physiological maturity when noted that
meter changes are slowed from one day to the next.


Harvesting
-SATURATION Harvesting should begin soon after physiological
maturity. Machinery should be in good repair and well
adjusted. Figure 13 illustrates the value of timely har-
vests in the midwest. Timely harvests are more impor-
ULL POINT tant in Florida on corn harvested in July and August
because of high populations of insects, and high tem-
t t t t peratures and humidity. High temperatures and hu-
10% 12% 13% 15% midity are ideal for diseases and sprouting of mature
I WATER REQUIRED corn.
FOR REFILL Corn combined at high moisture should be taken to
RE a dryer immediately and dried down to 13% moisture
I in a few hours or as fast as is practical. At 25 to 30%
moisture and high temperatures (90-1000F) common
during corn harvest in Florida, corn can only be kept
I I I I 80 safe from mold for a couple of days or less (Table 16). It
0 20 4 0 60 80 100 should be stored in clean, dry bins on the farm if avail-
TENSIOMETER READING (CB) able. On-farm storage can speed harvest by reducing
2. Relationship between soil-water content
d tension er reading for a loay fine hauling distance and command a high price by holding
and tensiometer reading for a loamy increases.
until the price of corn increases.


sanu plow layer. r ull poul 1s water cotn-
tent 24 hours following rain or irrigation.
Refill points are selected according to
crop needs and capacity of irrigation sys-
tem. (Quincy)


Measuring Yields
Yield measurements under various cultural prac-
tices is meaningful to producers for planning cultural









throughout the growing season, irrigation would be
unnecessary. However, as plants grow and mature,
water requirements often exceed the soil-water avail-
able for plant use and the plants become stressed.
Measuring soil-water throughout the growing season
can help in efficient utilization of irrigation water.
However, the relationship between soil-water content
of individual soils and tensiometer readings must be
known.
Figure 12 shows that% moisture in the soil changes
little from 20 to 100 centibars. Water schedules should
be determined from moisture tension rather than %
moisture in the soil.
The relationship between soil-water content and
tensiometer readings as shown for a loamy fine sand
plow-layer should be well understood. The full point for
this soil is at 5 centibar tensiometer reading or 25%
water content hv volume which is 3 in. per foot of
depth. An 8-in. plow layer would contain 2 in. of water
at the full point. If a tensiometer reading of 20 is se-
lected as the refill point (which corresponds to 15%
water by volume or 1.20 in. in the plowlayer) the amount
required to refill the plowlayer is 2 in. (full point), mi-
nus 1.20 in. (refill point) = 0.80 inches of irrigation
water needed. Frequency of irrigation will be deter-
mined by selection of soil refill point and age of plants.
By reading tensiometers daily the crop manager can
determine when and how much to irrigate from full


- 50

..J
0
o

>-

z 30
z
to
, Z
0
1-,




0
, 10


Fig. 12


and refill points for his particular soil conditions. When
soil reaches the refill point, irrigation should begin
immediately. Crops may be placed under stress condi-
tions for 3 or 4 days waiting for rains. This can reduce
yields, and eliminate yield increases from other good
management practices. Each field should contain at
least three tensiometers located at different positions
with respect to sprinklers.
Table 15 shows irrigation response of corn at three
selected refill points in a loamy fine sandy soil. High-
est yield was produced when the refill point was at a
tensiometer reading of 20. The peak water demand for
corn is about 0.25 in. per day during silking, tasseling
and grain filling periods; therefore, a 3-to-4-day irri-
gation frequency is required for optimum corn produc-
tion with inadequate rainfall.
When using tensiometers to determine the point to
begin irrigating, start early enough that areas covered
at the end of the cycle are not allowed to be above the
20 centibar level or water refill point for a very long
period. If 20 centibars is selected as the point to begin
irrigating, the first area could be watered at 15 centi-
bars. Soil moisture should be maintained by rainfall
and irrigation until plants have reached physiological
maturity and the black layer at the base of the kernel
begins to form. This point is reached at about 35% ker-
nel moisture. A moisture meter may give accurate in-
dication of physiological maturity when noted that
meter changes are slowed from one day to the next.


Harvesting
-SATURATION Harvesting should begin soon after physiological
maturity. Machinery should be in good repair and well
adjusted. Figure 13 illustrates the value of timely har-
vests in the midwest. Timely harvests are more impor-
ULL POINT tant in Florida on corn harvested in July and August
because of high populations of insects, and high tem-
t t t t peratures and humidity. High temperatures and hu-
10% 12% 13% 15% midity are ideal for diseases and sprouting of mature
I WATER REQUIRED corn.
FOR REFILL Corn combined at high moisture should be taken to
RE a dryer immediately and dried down to 13% moisture
I in a few hours or as fast as is practical. At 25 to 30%
moisture and high temperatures (90-1000F) common
during corn harvest in Florida, corn can only be kept
I I I I 80 safe from mold for a couple of days or less (Table 16). It
0 20 4 0 60 80 100 should be stored in clean, dry bins on the farm if avail-
TENSIOMETER READING (CB) able. On-farm storage can speed harvest by reducing
2. Relationship between soil-water content
d tension er reading for a loay fine hauling distance and command a high price by holding
and tensiometer reading for a loamy increases.
until the price of corn increases.


sanu plow layer. r ull poul 1s water cotn-
tent 24 hours following rain or irrigation.
Refill points are selected according to
crop needs and capacity of irrigation sys-
tem. (Quincy)


Measuring Yields
Yield measurements under various cultural prac-
tices is meaningful to producers for planning cultural










practices for the coming year. Economics can be ap-
plied to yield increases from cultural practices to de-
termine if the practice should be adopted by farmers in
their area.
When making comparisons between various treat-
ments, several rows should be planted with each treat-
ment in uniform areas of the field. The exact area with
each treatment should be marked immediately after
treatment and recorded. A single variety of corn should
be used across all treatments unless varieties are being
compared. Twelve or more rows of each treatment
should be compared to eliminate border effects. After
marking the location of each treatment, treat all areas
alike during the growing season.
At harvest time, equal areas of each treatment
should be marked off and harvested into individual
wagons. Weigh each load minus the weight of the wa-


gon and make yield calculations as follows:
1. Weight of crop in the wagon
2. Square feet of corn harvested (Row width in feet
x row number x row length in feet).
3. Acres harvested -
Row width x row number x row length (from above)
43,560 (square feet/acre)
4. Pounds of crop per acre -
Weight of crop in wagon
acres in test (from 3 above)
5. Percent moisture in crop (Determined with a
moisture meter)
6. Bushels per acre corrected for moisture con-
tent -
Wet weight corn (from 4)
lbs corn at moisture level
Table 17 gives corrected weights for shelled corn.


Bu/Ac
170
5 YEAR AVERAGE 8 HYBRIDS
TOTAL YIELD-------
160- HARVESTABLE YIELD
152.6
150 -. 145.4 146.4

140- 139.0 140.3

130-

120- 118.1

110

100
96.5
90 -| I I-
Sept I Oct I Nov I Dec I
HARVEST DATE
Fig. 13. Yields as influenced by date of har-
vest (DeKalb).


Table 16. Safe storage time for wet corn at various temperatures
and moistures, (with aeration) (Ga.).


Temperature F


Corn Moisture Content
15% 20% 25% 30%


1140
906
725
466
337
259
207
155
116


118Days
94
94
48
35
27
21.5
16.1
12.1


42
34
34
17
12.5
9.6
7.8
5.8
4.3


25
20
20
10
7.5
5.8
4.6
3.5
2.6


Table 15. Grain yields of irrigated corn at three
selected soil-water refill points placed
6" deep. (Quincy)

Tensiometer Number Total irri-
reading when of gation water Yield
irrigated irrigations applied (in.) bu/A
20 11 8.7 190
40 6 7.1 175
60 4 4.7 160
0 0 115


--









Table 17. Bushel weight, in pounds, of corn at given grain moisture corrected to 15.5% moisture.


Moisture

11.0%
.1
.2
.3
.4
.5
.6
.7
.8
.9
12.0
.1
.2
.3
.4
.5
.6
.7
.8
.9
13.0
.1
.2
.3
.4
.5
.6
.7
.8
.9
14.0
.1
.2
.3
.4
.5
.6
.7
.8
.9
15.0


Shelled

53.17
53.23
53.29
53.35
53.41
53.47
53.53
53.59
53.65
53.71
53.77
53.83
53.89
53.96
54.02
54.08
54.14
54.20
54.27
54.33
54.39
54.45
54.52
54.58
54.64
54.71
54.77
54.83
54.89
54.96
55.02
55.09
55.15
55.22
55.28
55.35
55.41
55.48
55.54
55.61
55.67


Moisture

15.3%
.4
.5
.6
.7
.8
.9
16.0
.1
.2
.3
.4
.5
.6
.7
.8
.9
17.0
.1
.2
.3
.4
.5
.6
.7
.8
.9
18.0
.1
.2
.3
.4
.5
.6
.7
.8
.9
19.0
.1
.2
.3


Shelled

55.87
55.93
56.00
56.07
56.13
56.20
56.26
56.33
56.40
56.47
56.53
56.60
56.67
56.74
56.81
56.87
56.94
57.01
57.08
57.15
57.22
57.29
57.36
57.43
57.70
57.57
57.64
57.51
57.78
57.85
57.92
57.99
58.07
58.14
58.21
58.28
58.35
58.42
58.49
58.57
58.64


Moisture
19.6
.7
.8
.9
20.0
.1
.2
.3
.4
.5
.6
.7
.8
.9
21.0
.1
.2
.3
.4
.5
.6
.7
.8
.9
22.0
.1
.2
.3
.4
.5
.6
.7
.8
.9
23.0
.1
.2
.3
.4
.5
.6


Shelled
58.86
58.93
59.00
59.08
59.15
59.23
59.30
59.
59.45
59.53
59.60
59.68
59.75
59.83
59.90
59.98
60.05
60.13
60.21
60.29
60.36
60.44
60.52
60.59
60.67
60.75
60.83
60.90
60.98
61.06
61.14
61.22
61.29
61.37
61.45
61.53
61.61
61.69
61.77
61.86
61.94


Moisture
23.9
24.0
.1
.2
.3
.4
.5
.6
.7
.8
.9
25.0
.1
.2
.3
.4
.5
.6
.7
.8
.9
26.0
.1
.2
.3
.4
.5
.6
.7
.8
.9
27.0
.1
.2
.3
.4
.5
.6
.7
.8
.9
28.0


Shelled
62.18
62.26
62.34
62.43
62.51
62.59
62.68
62.76
62.84
62.92
63.01
63.09
63.17
63.26
63.34
63.43
63.52
63.61
63.69
63.78
63.86
63.95
64.04
64.12
64.21
64.30
64.39
64.67
64.56
64.65
64.73
64.82
64.91
65.00
65.09
65.18
65.27
65.36
65.45
65.64
65.63
65.72


Moisture
.2
.3
.4
.5
.6
.7
.8
.9
29.0
.1
.2
.3
.4
.5
.6
.7
.8
.9
30.0
.1
.2
.3
.4
.5
.6
.7
.8
.9
31.0
.1
.2
.3
.4
.5
.6
.7
.8
.9
32.0
.1
.2


Shelled
65.91
66.00
66.09
66.19
66.28
66.37
66.46
66.56
66.65
66.75
66.84
66.94
67.03
67.13
67.22
67.32
67.41
67.51
67.60
67.70
67.80
67.90
67.99
68.09
68.19
68.29
68.38
68.48
68.58
68.68
68.78
68.88
68.98
69.09
69.19
69.29
69.39
69.49
69.59
69.69
69.80


Moisture
.5
.6
.7
.8
.9
33.0
.1
.2
.3
.4
.5
.6
.7
.8
.9
34.0
.1
.2
.3
.4
.5
.6
.7
.8
.9
35.0
.1
.2
.3
.4
.5
.6
.7
.8
.9
36.0


Shelled
70.11
70.21
70.32
70.42
70.53
70.63
70.74
70.84
70.95
71.06
71.17
71.27
71.38
71.49
71.59
71.70
71.81
71.92
72.03
72.14
72.25
72.36
72.47
72.58
72.69
72.80
72.91
73.03
73.14
73.26
73.37
73.48
73.60
73.71
73.82
73.94









Key Management Practices
1. Select the most productive land on your farm that
has been in a grass sod or a well fertilized legume
crop.
2. Plant corn in rotation with legume crop such as
peanuts or soybeans to reduce nematode, insect,
and disease losses. Where corn is planted after
corn, apply a nematicide in a furrow in a 7 to 12
inch band over the row. Nematodes are fast be-
coming the number 1 problem in crop production.
3. Use a soil test for both fertility and nematodes.
Soil and nematode tests may be obtained in Octo-
ber and November. Apply recommended kinds and
amounts of fertilizer and nematicides.
4. Apply a minimum of 50 lbs of elemental magne-
sium per acre if soil tests indicate low levels, and
apply micronutrients as needed. Lime should be
applied 2 to 4 months before the crop is planted to
obtain a pH of 5.8 to 6.4 for best results. Micro-
nutrients, except for boron which is easily leached,
may be applied 2 weeks before planting.
5. Use high quality seed of adapted varieties that
have proven yield potential.
6. Use at least two hybrids with no more than 1 week
difference in pollination date that have good lodg-
ing and disease resistance.
7. Subsoil where a hardpan exists. Subsoil in-row
after the pan has been confirmed by use of a
sharpened metal rod.
8. Plant as early as possible after February 15 when
soil temperature reaches 55.
9. Plan on having about 30,000 corn plants in 30"
rows under irrigation.
10. Seed rates with early planting and no-till plant-
ing need to be increased by 15% to obtain the
highest recommended population with these prac-
tices on either irrigated or non-irrigated fields.


11. Control weeds by proper crop rotations, deep plow-
ing, herbicides, cultivation, and crop competition.
12. Control nematodes by using rotations with other
crops and nematicides.
13. Nematode tests should be a routine practice to de-
termine levels on a yearly basis after crop harvest.
14. Scout fields for insect, disease, nutrient, or weed
problems. Fields should be checked twice weekly
to detect problems in an early stage.
15. Use disease resistant varieties.
16. Fertilize according to soil tests. About 240 lbs of
nitrogen is adequate for high yields when applied
in split applications.
17. The initial nitrogen application should be banded
to the side and below the seed.
18. Where soil tests indicate high levels of phospho-
rus and potash, response to starter fertilizer would
be little especially if nitrogen was banded at
planting.
\'I9. Irrigate to prevent moisture stress.
20. Tensiometers should be used to schedule irriga-
tion at 20 cb of moisture tension.
21. Harvest as soon as the moisture content of the
grain is at 30%.
22. Dry promptly and store at 13% moisture.
23. Adjust the combine to obtain maximum harvest-
ing efficiency.
24. Keep accurate records of all production inputs and
any special problem that arises during the grow-
ing season.
25. Set aside 5 to 10 acres each year to try new prac-
tices that have given yield increases and use pro-
duction records to determine if they are economical
for your farm operation.
26. Consult your county extension agent for up-to-date
information on varieties and other specific infor-
mation that is needed to produce high corn yields.


Use of trade names in this publication is solely for the purpose of providing specific information. It is not a
guarantee or warranty of products named and does not signify approval to the exclusion of others of suitable
composition.














Conversion Chart (approximate)
Multiply ounces by 30 = milliliters
Example: 16 ounces = 16 x 30 = 480 milliliters
Multiply pints by .47 = liters
Example: 1.5 pints = 1.5 x .47 =.71 liters
Multiply quarts by .95 = liters
Example: 2 quarts = 2 x .95 = 1.9 liters
Multiply gallons by 3.8 = liters
Multiply liters by 2.1 = pints
Multiply liters by 1.06 = quarts
Multiply liters by 0.26 = gallons
Multiply ounces by 28 = grams
Multiply pounds by 0.45 = kilograms
Multiply short tons by 0.9 = metric tons
Multiply grams by 0.035 = ounces
Multiply kilograms by 2.2 = pounds
Multiply inches by 25 = millimeters
Multiply feet by 30 = centimeters
Multiply yard by 0.9 = meters
Multiply miles by 1.6 = kilometers
Multiply meters by 1.1 = yards
Multiply kilometers by 0.6 = miles
Multiply square feet by 0.09 = square meters
Multiply acres by 0.405 = hectares
Multiply hectares by 2.47 = acres
Multiply kilogram/hectare by 0.89 = pounds/acre
Multiply inches by 2.54 = centimeters
Multiply centimeters by 0.39 = inches

Weights and Measures
1 Rod = 16V2 feet
1 mile = 320 rods
1 mile = 5280 feet
1 cubic foot = 1728 cubic inches
1 cubic yard = 27 cubic feet
1 cord (wood) = 128 cubic feet
1 standard bushel = 2150.42 cubic inches
1 cubic foot = about 4/5 of a bushel
1 peck = 8 quarts
1 bushel = 40 pecks
1 gallon = 269 cubic inches
1 gallon = .005761 cubic yards
1 bushel = 35.24 liters
1 acre = 43,560 square feet











DEC 1 0



FEB i.8 8 FEB 1 8131


This public document was promulgated at a cost of $819.46, or 41 cents per copy, to provide information on irrigation
in corn production. 9 2M 80


COOPERATIVE EXTENSION SERVICE, UNIVERSITY OF FLORIDA, INSTITUTE OF FOOD AND AGRICULTURAL
SCIENCES, K. R. Tefertiller, director, In cooperation with the United States Department of Agriculture, publishes this infor-
matlon to further the purpose of the May 8 and June 30, 1914 Acts of Congress; and is authorized to provide research, educa-
tional Information and other services only to individuals and Institutions that function without regard to race, color, sex or
national origin. Single copies of Extension publications (excluding 4-H and Youth publications) are available free to Florida
residents from County Extension Offices. Information on bulk rates or copies for out-of-state purchasers is available from
C. M. Hinton, Publications Distribution Center, IFAS Building 664, University of Florida, Gainesville, Florida 32611. Before publicizing this
publication, editors should contact this address to determine availability.




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