E 38—Lancaster Farming, Saturday, August 18,1984
Try checkbook method for scheduling corn
NEWARK, Del. With record
high prices possible by harvest
time, com producers will want to
have plenty to sell. Since irrigation
is the best way to ensure a bumper
crop on Delmarva, many growers
put in new center-pivot systems
this year.
Last summer at least three
farms in Sussex County grew over
200 bushels of com per acre under
irrigation, so this is a realistic goal
on sandy soils, according to
University of Delaware extension
agricultural engineer Tom
Williams. The state record is 291
bushels on an irrigated silt loam.
It takes a lot of water to grow
200-bushel com, though-about 25
inches or 700,000 gallons per acre
total, applied as irrigation and ram
at the right tune throughout the
growing season.
Research at the University of
Delaware Agricultural Ex
periment Station has shown that
corn water use starts slowly in
May (1.7 inches), accelerates in
June (5.4 inches), peaks in July
(9.5 inches), declines in August
(7.5 inches) and ends at maturity
in September (1.3 inches).
July is the most critical month,
with corn water use peaking at
about 0.32 inches a day during
pollination. To keep up with this peak
demand when no ram falls and
there’s limited soil moisture stored
in the root zone, Williams says an
irrigation system with 75 percent
efficiency would have to supply 8
gallons per minute per acre con
tinuously (24 hours a day, 7 days a
week).
“Scheduling irrigation is a real
challenge in the East where rain
can mess up your schedule but
save on pumping costs,” he says.
“Too little water reduces yields;
too much leaches out valuable
plant nutrients.”
He recommends growers use
what he calls a “checkbook
method” to keep track of available
water, so that they know when to
turn their systems on and off for
maximum benefit to the crop.
Rainfall and irrigation water are
the deposits to the account. Com
water use is the withdrawal. Orte
point to remember is that the
account can’t exceed the soil’s
water-holding capacity in the root
zone. So growers must know how
much water their soil will hold and
how much is available for plant
growth. This can vary from less
than 1 inch per foot to over 2.5
inches per foot. Coarse textured
soils hold the least amount of
available water. The Soil Con-
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servation Service and the
Cooperative Extension Service can
both provide information on soil
type and moisture-holding
capacity in individual fields.
Next, a farmer using this water
accounting method should
determine the crop rooting depth.
According to Williams, corn
usually reaches its maximum
rooting depth by tasselhng time.
“Roots may reach down 4 feet,” he
says, “but our studies have shown
that most of the water is drawn
from the top foot of soil. If you
don’t want to dig a few holes and
look for roots, assume a 2-foot
rooting depth. This sets the limit on
how large your soil water account
can get. Rooting depth times
available moisture per foot equals
the maximum amount of water
available to the crop.”
When the water account is down
to half this amount, it’s time to
irrigate. In other words, irrigate
when the soil moisture deficit is 50
percent of the available soil
moisture capacity within the
major root zone.
Growers can estimate how fast
water is being withdrawn by the
com crop in a number of ways, but
one of the easiest methods is to
simply read it off the graph of com
water use developed at the
University of Delaware. (Copies of
this graph are available at county
extension offices in Newark, Dover
or Georgetown, or by calling
Williams directly at 451-2468).
Here’s an example of how to
estimate the rate of water use.
Assume it’s the second week in
July and com is pollinating, using
0.32 inches of water per day. If the
soil mosture-holding capacity is 1
inch per foot and the major rooting
depth is 2 feet, when the soil is at
field capacity after a heavy ram or
irrigation, the maximum water
available will be 2 inches. Under
these conditions, the crop should
be irrigated when 1 inch of water
has been withdrawn or used.
That means the com needs to
receive 1 inch of water every 3
days until the end of July, when
water use starts to decline.
“If you set the system to apply 1
inch of water,” says Williams, “an
efficiency of 60 to 90 percent will
leave a margin of safety in your
water account for some rain. If the
system is 70 percent efficient, then
you’re still 0.30 inches short of
filling the soil back up to field
capacity.”
The probability of receiving 0.30
inches of rain within a 3-day period
in July in southern Delaware is
CALL OR WRITE:
about 40 percent. So, in four years
out of 10, rainfall will make up the
difference. But in six years out of
10, the irrigation system will have
to make up the difference. “Take
this into consideration in
managing your water account,”
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PENNSYLVANIA
Barrett Equipment Co.
Smicksburg, Pa
814-257-8881
Clapper Farm Equip., Inc,
Alexandria, Pa
814-669-4465
Fred Criveliaro
Easton, Pa
215-258-7584
Tom Dunlap
Jersey Shore, Pa
717-398-1391
Erb & Henry
New Berlmville, Pa.
* 215-367-2169
Fickes Silo Co.
Box 7
Newville, Pa. 17241
717-776-3129
Hines Equipment
Cresson, Pa.
814-886-4183
J & M Machinery Co., Inc.
Greensburg, Pa
412-668-2276
S.G. Lewis & Son, Inc
West Grove, Pa
215-869-9440
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With a little programming, he
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Every bookkeeping system
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Marshall Machinery, Inc,
Honesdale, Pa
717-729-7117
MKS Enterprises, Inc
Hanover, Pa
717-637-2214
Northeast Equipment Co.
Northeast, Pa
814-725-1888
Soilenberger Silos Corp. .. - .
Chambersburg, Pa Sharon Springs Garage, Inc.
717-264-9588 Sharon Springs, NY
518 284 2346
Swope & Bashore, Inc
Myerstown, Pa
717-933-4138
Roller Mixer
Name
City
R.T. Markle
Farm Equip., Inc.
State College, Pa
814-237-3141
North Penn Sealstor
Bloomsburg, Pa
717-387-1422
Atlee Hebert
Littlestown. Pa.
717-359-5863
Rovendale Supply
Watsontown, Pa.
717-538-5521
Stouffer Bros., Inc.
Chambersburg, Pa
717-263-8424
irrigation
balanced. In irrigation schedulini
soil tensiometers serve that fum
tion. They will indicate when th
bookkeeping is getting ahead of c
behind actual soil moisture coi
tent.
(Turn to Page E 39)
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State
Tam Agri Corp.
Dillsburg, Pa
717-432-9738
Terre Hill Silo Co., Inc
Terre Hill, Pa
215-445-6736
Uniontown Farm Equipment
Umontown, Pa
412-437-9851
MARYLAND
Arnett’s Garage
RR 9 Box 125
Hagerstown, Md.
301-733-0515
NEW JERSEY
Brookhill Equipment
& Supply Co.
Pittstown, NJ
201-735-4142
lEW YORK
ESI VIRGINIA
Ed Lipscomb’s Equip
Eglon, WV
304-735 5239