P34—Lyicastw Fanning, Saturday, April 21,1984
Can drip irrigation be used in
NEWARK, Del. The same
amount of water has been on the
earth since the beginning of time
and there’s not much we can do
about it, says University of
Delaware professor emeritus and
agronomist William H. Mitchell.
Though the total supply is great,
only about 1 percent is available
for homeowners, industry and crop
irrigation probably in that or
der. Hie rest is tied up in icecaps
and saltwater.
“As we go from doughts to floods
and back to droughts again, it’s
usually the last event that sticks in
our minds,” Mitchell says. “This is
what makes planning for
responsible water use so difficult.
Many parts of the eastern U.S.
have experienced serious droughts
in the past decade, but progress
toward more efficient water use
drops to a trickle as soon as it
starts raining. We seem unable to
accept that it will probably be
worst the next time around, even
though acknowledged authorities
predict that by the year 2000 a
mere 16 years from now national
water consumption will increase
by 33 percent.”
Irrigation represents the largest
single use of freshwater in the U.S.
In 1955 it consumed half the total
available water, and the propor
tion continues to grow. “As
demands for water increase and
supplies tighten, will agricutlure
be able to get what it needs?” asks
Mitchell. “Studies have shown that
in some parts of the U.S., industry
can afford to pay SO times as much
for water as can agriculture. It’s
clear who will get the water in a
competitive market.”
These are sobering facts, facts
that lead many to believe the
country’s next resource crisis will
involve water especially water
for food production.
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Mitchell and others familiar with
the benefits of drip or trickle
irrigation believe this system can
offer at least a partial solution to
such problems. Their high hopes
are based largely on its potential
for efficient water use and the
reduced energy costs associated
with low operating pressures. In
addition, it is well suited to small,
irregular fields, the agronomist
says. Pivot irrigation is the first
choibe on large symmetrical fields
and is likely to remain so, at least
for the present.
Currently, trickle irrigation is
used primarily on high value
vegetable, fruit and nursery crops.
When tubing must be replaced
annually, this cost is considered an
acceptable tradeoff with these
crops, given the system’s many
positive features, which include
earlier and higher yields. For the
future, however, Mitchell believes
the system’s greatest potential will
lie with more extensive crops such
as field corn particularly in
small fields.
Some technological im
provements must be made before
trickle systems will be economical
on lower value crops, the
agronomist says. For one thing,
drip irrigation must be able to
function without lateral line
replacement for 10 years or more.
“This will reduce the annual
capital investment cost,” he says,
“though it will add new challenges.
The lateral tubing must be plug
free, and suitable for subsurface
placement. It should also be able to
deliver plant nutrients and
pesticides to the root zone.’,’
Coming up with such a system is
a formidable assignment, the
agronomist admits. Components
already exist, but there are
missing parts and it will take
dedicated research and
development to put the package
together. He believes the effort will
be well repaid if the payoff is
reduced unit production costs and
a more conserving use of water.
Shortly before his retirement
last December, Mitchell com
pleted a 10-year irrigated field
com study on the Delaware
Agricultural Experiment Station’s
Newark research farm, using drip
tubing buried at a depth of 14 in
ches. Lateral lines were about 200
feet long, laid out on 36-inch cen
ters riming perpendicular to a
prevailing 3 to 5 percent slope.
Unfiltered municipal water was
applied through the system at a
pressure of 5 psi. The chlorinated
water contained a moderate
amount of iron which was clearly
visible on the interior walls of the
tubing but did not appear to limit
its performance.
The study included both
broadcast fertilizer and anhydrous
ammonia subsurface fertigation
treatments. All feed lines were
well below the depth of tillage
operations, which included annual
moldboard plowing. The soil was a
highly fertile silt loam with a
water-holding capacity of about 2
inches per foot of soil.
“The most striking fact to
emerge from the study,” reports
Mitchell, “was that after 10 years
the system functioned as well as it
did during the first year. It proved
to be an excellent carrier of
anhydrous ammonia. Sequential
ammonia applications to deliver
100 pounds of nitrogen through the
system increased nitrogen ef
ficiency and consistently produced
top yields.”
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In 1983, the final year of the
study, 100 pounds of N delivered
this way produced about the same
yield as 175 pounds broadcast prior
to plowing.
“With refinements,” says
Mitchell, “this system could be
scaled up to practical size and be
competitive with sprinkler
systems on small fields, using less
water and nitrogen than con
ventional irrigation.”
Some irrigation needs can’t be
met by subsurface irrigation, the
scientist admits. And, as with any
new development, there will be
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tests indicate it may also have
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unforseen problems to solve as the
system goes into more general use.
“Rocky fields, sloping land,
water impurities and restricted
movement of capillary moisture in
sandy soils place obvious limits on
trickle irrigation,” he says.
“Improved technology through
research and development will
solve many of these difficulties.
Others will be harder to handle.
But, all in all, the limitations are
few when balanced against trickle
irrigation’s potential for water,
nutrient and energy con
servation.”
intermediate resistance to Nor
thern com leaf blight. It is
susceptible, however, to an
thracnose stalk rot and common
leaf rust.
DEBII has upright leaves above
the ear, good flowering synchrony
and two-eared tendency at low
plant populations. It has purple
silks, red cob and yellowish-brown
(bronze) kernels. Pollen
production is rated good and seed
quality is average.
Limited yield trials indicate that
DEBII has satisfactory combining
ability and should be tested with
inbreds of both Lancaster and Stiff
Stalk groups.
Only three other public inbred
field corn lines have second brood
corn borer resistance, Hawk says,
and it is likely that DEBII is a new
source, since it is not related to
these lines.
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