Page 14-Corn Talk, Lancaster Farming, Saturday, July 17,1993
TILLAGE AND
CROP ROTATION
EFFECTS ON
CORN YIELDS
Greg Roth
A recent study published in
the Journal of Production Agri
culture by M. G. Lund, P. R.
Carter, and E. S. Oplinger eva
luated the effects of two tillage
systems no-till and mold
board plowing and crop
rotations (continuous cropping,
com/soybean, wheat/soybean/
com, and soybean/wheat/com)
on the growth and yield of com
wheat and soybeans.
The study showed that conti
nuous cropping reduced yields
of com by 10 percent and soy
bean by 15 percent compared to
when die crops were in rotation.
Generally, yield, reductions
because of continuous cropping
were greatest under no-till.
The effects of rotation and
tillage were less consistent on
wheat as the effect varied from
none in one year to a 36 percent
reduction in another. With
wheat, the tillage influence on
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the rotation effect was less con
sistent in some years the
tilled plots were most affected
and in another year when Sep
toria and leaf rust diseases were
severe, no-till treatments were
more affected by continuous
cropping.
Com yields were similar in
each of the three rotation sequ
ences except for no-till com
after wheat, where yields were
reduced by 6 percent. The
authors suggest that the same
allelopathic factors that reduce
yields of com following rye
may cause the yield reductions
following wheat, since the early
season com was about 8 inches
shorter than the no-till com fol
lowing soybeans. In this study,
the straw from the wheat was
not baled or removed and this
may have increased the poten
tial for allelopathic effects.
This study did not show any
difference in soybean yields for
a one- or two-year rotation.
Some previous research has
shown a benefit from increas
ing the time between soybeans
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in the rotation to more than just
one year, but the authors sug
gest it may need to be more than
two years as they had in this
study to be significant.
In summary, the study did
not show any consistent
improvement in com and soy
bean yields by going to a three
year rotation, including wheat.
In Pennsylvania, the advan
tages of wheat in a rotation may
be greater than in this study for
several reasons:
• In southeast Pennsylvania,
wheat yields are not reduced by
late planting following com
and soybeans as much as they
are in Wisconsin.
• In some areas, soybeans
can be double cropped with the
wheat, adding to the profitabili
ty of the wheat.
• Control of perennial weeds
in no-till programs can be suc
cessful following wheat
harvest.
A common problem with
surface applications of urea
containing fertilizers such as
urea and UAN solution is the
potential for a significant loss
of N from the fertilizer by
volatilization.
The results of a three-year
study designed to evaluate the
effect of application timing and
method of liquid nitrogen
(UAN) to com was recently
published in the Journal of Pro
duction Agriculture. The study
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NITROGEN
MANAGEMENT
OF UREA-AMMONIUM
NITRATE SOLUTION
(UAN) IN
NO-TILL CORN
Greg Roth
Doug Beegle
/
/
/
<Mor
mm TPMJK MIWS
was performed by Richard Fox
and William Piekielek, from
the Department of Agronomy
at Penn State.
In this study, UAN applica
tions were made either at plant
ing or at sidedressing. The at
planting treatments were either
dribbled or sprayed on. The
sidedress applications w«k|
dribbled between the rows or
injected.
All except the injected treat
ments were applied with one of
three urease inhibitor treat
ments none, ammonium
thiosulfate, or an experimental
compound called NBPT.
Urease inhibitors, if effective,
should inhibit ammonia volatil
ization losses from surface
applied urea fertilizer.
The three-year average
results showed that injecting
UAN at sidedressing produced
the most yield (129 bushels/
acre) and spraying UAN at
planting the least (114 bushels/
acre). The dribble at planting
(121 bushels/acre) and the
dribble sidedress yields (124
bushels/acre) were
intermediate.
The study indicates that to
obtain the highest yields, pro
ducers should consider apply
ing N at sidedressing in either a
band or injected application.
About one-half of the studies
in the literature have shown a
response to injecting UAN at
sidedressing, while the others
have shown no benefit com
pared to banding.'
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In this case, assuming
S2.SO/bushel corn, the
5-bushel-per-acre advantage
with injecting would have been
profitable.
Of the two inhibitors eva
luated. NBPT and ammonium
thiosulfate. NBPT was the most
consistent at increasing the effi
ciency of the fertilizer applica
tion. Fbr UAN sprayed on at
planting, there was a 7-bushel
per-acre advantage to adding
NBPT. Unfortunately, NBPT is
not yet commercially available.
There was no advantage in
adding ammonium thiosulfate
when spraying UAN. This is
consistent with the findings of
several other researchers.
Neither of the inhibitors
showed any advantage when
applied in banded applications.
The researchers were also
able to estimate losses from
surface-applied urea applica
tions. In the three different
years of the study, they esti
mated 29, 11, and 27 percent
loss from applying these fertil
izers to the surface.
The losses in the first and
third years occurred when there
were four days between appli
cation and 0.4 inch of rain fell.
In the second year, when the
loss was smaller, there was only
one day until 0.4 inches of rain
fell.
The researchers recommend
that the most efficient ways to
apply UAN are to dribble or
inject at sidedressing.
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