Techniques of Sidedressing N
Lloyd Murdock and Greg Schwab, Plant
and Soil Sciences
costs of fossil fuels are an indicator that nitrogen (N) fertilizer
prices are likely to remain high for the foreseeable future. With
higher N prices, techniques that improve fertilizer N efficiency are
more attractive. Sidedressing is one of the options.
sidedressing is the best method for applying N on corn, its
effectiveness is greatly determined by soil drainage. Well drained
soils have very little loss of N when preplant is compared to
sidedress applications. Therefore, there is no difference in the N
recommendation between the two methods for well drained soils.
drained soils commonly lose substantial amounts of N that is applied
before planting. When compared to preplant recommendations, sidedress
N recommendations are reduced by 35 lb/a, because sidedress N is more
efficient on poorly drained soils.
The method of
sidedressing determines its effectiveness and depends on the type of
tillage, N fertilizer form and placement in or on the soil.
Low Residue Cover
Soils that are
tilled causing less than 30% of soil surface to be covered by residue
makes the sidedressing decisions easier. Almost any method or
fertilizer form works well here. Although it is sometimes better to
inject N than to surface broadcast or stream it on the soil, the
differences are usually small. Since volatilization of N from surface
placement (except for Anhydrous Ammonia or urea on very high pH soils)
is usually small, about any type of N fertilizer can be used with
equal effectiveness. However, injecting the fertilizer into the soil
always has less risks of loss.
tillage is used one must carefully consider the differences in
effectiveness of N sources and placement options.
application becomes more important because this places the N below the
residue layer and prevents losses of N. It reduces the chance of
applied N being partially tied up by the microbes in the residue
decomposition process, and prevents the volatilization loss of the
urea portion of UAN liquid fertilizer. Commonly, subsurface placement
results in a 10-20% increase in the efficiency of the applied N as
compared to a surface application.
The type of
fertilizer N used for surface broadcast in high residue conditions
also has a big effect on efficiency of the sidedress operation. Any
fertilizer containing urea has a potential for N loss due to ammonia
volatilization. The other type of N loss, when some of the N is
tied-up by the microbes decomposing the residue (immobilization),
which occurs with this method, exists with any form of surface applied
losses for surface applied sidedressed urea are commonly in the 0 to
20 percent range but can be higher. The losses depend on soil
temperature, soil moisture, amount of surface residue, soil pH, and
length of time between application and the first rain event or
irrigation. Nitrogen volatilization losses from urea fertilizer
applied prior to May 1 are generally low. After May 1, N loss is
greatest with urea applied on high residue and moist soil with a warm
breezy drying period.
can be greatly reduced if a urease inhibitor is used with the surface
applied urea fertilizer. Urease inhibitors reduce the activity of the
urease enzyme for up to 14 days. As long as it rains during this
14-day period, the urea will be moved into the soil without the risk
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Nitrogen Rates For Corn: Why No Soybean Credit?
John H. Grove, Plant and Soil
nitrogen (N) prices are very high this year. Corn growers are
carefully examining their N management protocol, especially their
fertilizer N rate, looking to cut costs and conserve corn’s profit
potential. UK’s recommendations suggest growers consider soil
drainage, tillage, fertilizer N timing, nitrification inhibitor use,
winter annual legume cover crops and previous crop as they select the
fertilizer N rate for each field of corn. However, Kentucky producers
have noticed that one important previous crop, soybean, does not
result in an adjustment to the recommended corn N fertilization rate.
Previous crops of corn, soybean, wheat, and grain sorghum all result
in the same fertilizer N rate recommendation. Public universities in
states north of the Ohio River give an N credit, usually 1 lb of N per
bushel of previous soybean yield, against the fertilizer N rate for
corn after corn. Why the difference in recommendations?
research data does not support giving an N credit when corn follows
soybean, relative to continuous corn. Figure 1 illustrates some of our
latest data (average of 2004 and 2005 production years) on this
subject. No-till corn was grown on Maury silt loam after corn,
soybean, and grass/clover hay. Rates of fertilizer N ranged from 0 to
200 lb N/acre, using ammonium nitrate, and were applied just after
planting. Prior doublecrop soybean yield averaged 44 and 50 bu/acre in
2003 and 2004, respectively. Corn yield responses to fertilizer N rate
were fitted to curvilinear-plateau models. The solid vertical lines
indicate the N rate where each model found no further yield response.
The solid vertical lines for corn after corn and corn after doublecrop
soybean fall into the area between vertical dashed lines, which
represent the range in UK fertilizer N rates recommended for no-till
corn following another grain crop on well-drained soil. The solid
vertical line for corn after grass/clover hay fell well outside (and
below) that range.
benefit to crop rotation was 10 or 25 bushels/acre when corn followed
grass/clover hay or doublecrop soybean, respectively. This benefit was
independent of the yield response to fertilizer N rate. Clearly,
larger amounts of N fertilizer will not get continuous corn to yield
as well as corn grown in rotation.
Why is the N
benefit to corn following soybean so small? Unlike more northern
states, much of Kentucky’s corn and soybean residues decompose during
our mild fall and winters. The N released from soybean residue is lost
via denitrification and leaching, leaving little for an “N credit”
next spring. In continuous corn, residue breakdown reduces the amount
of this high C:N material that would immobilize (tie-up) fertilizer N
applied next spring. Thus, late fall through early winter
decomposition of our corn and soybean residues diminishes the
influence of these previous crops on the optimal rate of fertilizer N
for the following corn crop. The data in Figure 1, as well as earlier
data from the mid-1990’s, indicate that the N benefit to corn after
soybean is small (and falls within experimental error). Kentucky corn
growers need merely to adjust their fertilizer N rate within the
recommended range, using rates in the lower part of the range when
corn follows soybean.
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Habits for High
Chad Lee, Plant and Soil Sciences
Recently, I spoke
to a group of farmers on the keys and habits for producing high corn
yields. While none of the topics were necessarily new to the farmers,
the concepts were timely. The increased costs of seed, fertilizer,
fuel and land rents have caused many farmers to consider cutting costs
or corners to alleviate some of the pressure. In the rush to save
money, now is a good time to review the concepts of producing high
There are four
keys to high corn yields:
Maximize days suitable for growing
90 to 95% light interception at or close to silking (R1)
Adequate nutrients, water and air to complete plant growth and
each of these four keys, the odds for producing high corn yields are
genetics starts with a high-yielding hybrid and includes stress
tolerance and defensive traits such as disease tolerance. The best
measuring stick we currently have for stress tolerance is yield over
multiple locations. Different stresses are imposed at each location
and hybrid performance across locations is good indicator of general
stress tolerance. Disease tolerance is not necessary every year or in
every field, and disease tolerance is difficult to evaluate. Seed
companies do their best to provide accurate disease information, but
hybrids will sometimes perform differently in the field.
suitable for growing includes selecting the proper hybrid maturity,
timely planting, and hybrid stress tolerance. A hybrid that takes
about 113 to 117 days to mature is optimal for Kentucky. Hybrids in
this maturity group typically perform the best in Kentucky. Exceptions
do occur, as in 2005, when the later-maturing hybrids benefited from
the late-season rainfall. Optimal planting dates in Kentucky are
middle to late April for western Kentucky and early May for central
and eastern Kentucky. Hybrid stress tolerance was discussed earlier.
Achieving 90 to
95% light interception at or close to silking (R1) is affected by
seeding rate, row spacing, planting date, hybrid maturity and proper
weed management. Current UK recommendations will accomplish maximum
light interception close to silking. Those recommendations include
seeding rates between 22,000 and 30,000 seeds per acre, a row spacing
of 30 inches, timely planting, hybrid maturities of 113 to 117 days,
and good early season weed control. The ability of corn in 30-inch
rows to achieve 90 to 95% light interception at silking is one of the
reasons that we normally do not see yield increases from narrow rows.
adequate nutrients, water and air in the soil to complete plant growth
and seed fill includes adjusting soil pH, adding the proper amount of
N, P, K, and Zn, precipitation, water infiltration and water
availability. A soil test is required for accurate adjustments to soil
pH, P, K and Zn. While no one can control the amount of rainfall
(except by irrigation), water infiltration and water availability can
be managed by conserving soil organic matter and reducing soil
compaction. Soil compaction will limit water infiltration, reduce
water availability and reduce air available to the plant. Reduced
tillage and no-tillage are two methods that both conserve soil organic
matter and typically reduce soil compaction.
There are at
least 10 practices that will allow a farmer to optimize the four keys
to high corn yield.
Know which fields should be planted to corn.
Tillage (as little as possible): deep ripping, if necessary;
no-till where possible.
Select high-yielding hybrids.
Fertilize according to soil test.
N application: timely and adequate.
Higher seeding rates on better soils; but not too high
Effective, timely pest management control
Monitor the crop to handle problems this year and learn for
practices make sense in theory, but they are not always easy to
accomplish in practice. The window for optimal planting in Kentucky is
about a week. However, there are very few operations that can plant
all their corn acres within a week. So, while these 10 habits will
optimize the 4 keys to high yields, real life often makes achieving
these habits difficult.
researchers are looking at ways to alleviate the demand for timely
planting. See the related article in this newsletter. In conjunction
with county agents, we have investigated seed coating technology (Intellicoat
brand) to see if we can plant corn early and delay emergence until the
optimal time. Those results were mixed and we are not recommending
that technology at this time.
While the 10
habits and 4 keys presented here are not necessarily new to anyone,
they are a reminder of the basics behind corn production. By keeping
these 10 habits and 4 keys in mind when considering how to manage
inputs, each farmer can determine how to maximize returns in his or
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Jim Herbek, Plant
and Soil Sciences
The “ideal” goal
in planting corn is to choose the optimum planting date that will
result in the highest yield potential. However, various factors such
as weather (dominant factor), management capabilities, and management
risk strategies play a significant role in whether the optimum
planting date is achieved by a farmer for his total corn acreage.
The risk of planting too early or too late for optimum yield is a
compromise that many farmers face. The optimum planting date will
vary, not only by region, but can also vary among growing seasons.
Corn planting date research indicates the “normal” optimum planting
date period; but because of yearly weather fluctuations, the optimum
planting date may deviate somewhat from “normal” for any specific
year. However, over the long term, the “normal” optimum planting date
period provides the best probability for obtaining maximum corn yield
corn is normal for farmers because many feel they cannot afford to
wait for perfect conditions to begin planting. Early planted corn does
provide advantages which include: getting a “head start” on planting
to avoid weather delays that may result in yield penalties for later
plantings; and early plantings also result in the critical pollination
time occurring at a more favorable time period than later planting
dates. Planting early does not always guarantee optimum yields,
particularly if planting occurs too early under less than ideal
How early can we
start planting corn? When deciding to start, consider soil conditions
(temperature and moisture), calendar date and past experience as
guides. Soil temperature is very critical. Average soil temperatures
are lower for early plantings and can result in less than ideal stands
from delayed corn germination and emergence. Since corn will not
germinate below 50ºF, it is very risky to plant corn if soil
temperature at planting depth has not reached this minimum
requirement. It will take corn at least three weeks or more to
germinate and emerge if soil temperature does not increase much above
50ºF after the seed has been planted; which can occur if there is a
prolonged cool and wet period after planting. The longer the seed
remains in cool soils before emergence, the more subject they are to
soil diseases and insects and the greater the risk of reduced and
non-uniform stands. Planting corn early is preferred when minimum soil
temperature requirements have been met and there are good weather
forecast prospects for an increase in soil or air temperatures that
will promote more rapid emergence. Constant soil temperatures of
55-60ºF should result in expected corn emergence in about 2 weeks.
Optimum soil temperatures for emergence occur above 60ºF.
have a daily fluctuation cycle and can vary as much as 5-10 degrees
each day (day-time highs and night-time lows) in the spring near the
soil surface (planting depth). This implies that if corn seed is
planted very early, it may not be subjected to a constant soil
temperature of at least 50ºF to promote continual germination and
growth, which is critical for early planted corn. The daily soil
temperature fluctuation will be influenced by air temperature, solar
radiation, and also soil moisture. Soil temperatures reach a maximum
during mid-day. If soil temperatures have a minimum of 50ºF at
planting depth early in the morning and at least 55ºF during mid-day
for several consecutive days, this is a “reasonably good” guide to
start planting corn.
provides an approximate guide when average soil temperatures of 50ºF
normally occur in various regions of Kentucky. Based on historical
weather data, an average weekly soil temperature of 50ºF “normally”
occurs at planting depth under bare soil in mid-March in
southwest Kentucky, in late March to early April in west and central
Kentucky, and early to mid-April in eastern Kentucky. However, because
environmental conditions vary each spring, the average weekly soil
temperature of 50ºF can occur from one to two weeks earlier or later
than the “normal” dates for each region. Because of this yearly
variation, actual soil temperature and not calendar date is the best
guide to use for early planting. Keep in mind that soil temperature
for no-tillage plantings will not warm as early as tilled soils
because of residue cover. Depending on the amount of residue, soil
temperatures can be as much as 5 degrees cooler than bare soils. As a
result, no-till corn planting may have to be delayed several days as
compared to tilled soils.
Corn also has an
ending optimum planting period, based on calendar date which, if corn
is planted beyond this date, will result in less than maximum yield.
This “last” optimum planting date is based on planting date research
for an area or region and provides an “average” calendar date(s) for
corn planting to be completed to avoid a yield loss. Because of
variations in environmental/weather conditions each growing season,
the “last” optimum planting date may deviate somewhat each year from
the “average” date.
A multi-year corn
planting date study was conducted in west Kentucky at the University
of Kentucky Research and Education Center to determine an optimum corn
planting date period. This study was conducted for six years
(2000-2005) and included five planting date periods starting in early
April at intervals of about 2-2½ weeks. Two medium maturity corn
hybrids (non-Bt and Bt hybrid isolines) were used. The study was
no-till planted. The yield data for this corn planting date study is
contained in Table 1.
Over the 6-year
period, average optimum yield was obtained during the mid-late April
planting period. Optimum yield consistently occurred during this
planting period each of the six years.
The early April
planting period yielded slightly less (average of 7%) than the
mid-late April planting period. In only one of the six years (2002),
did the early April planting period have significantly equal yields to
the mid-late April planting date.
The early May
planting was the critical planting period for yield loss to occur as a
result of planting too late. There was an average yield loss of 8%
during this planting period. However, three of the six years (2001,
2004 and 2005), the early May planting period produced yields
significantly equal to the optimum planting period of mid-late April.
For the other three years (2000, 2002, and 2003), yields were
significantly reduced during the early May planting period.
made after early May, corn yield losses were even greater. For
planting periods of mid-late May and early June, average yield losses
of 18% and 38% occurred, respectively, compared to the mid-late April
planting period. An average yield loss of about 1%/day occurred if
corn was planted beyond May 1.
progress each Spring will be determined by the weather conditions
(moisture and temperature) that occur. Based on recent corn planting
progress data from the Kentucky Agricultural Statistics Service, about
15% of the corn acreage in Kentucky is normally planted by April 10.
However, this has ranged over the last five years from about 35% in
2004 to less than 10% in 2001 and 2005. Normally, 60-65% of the corn
acreage in the state is planted by May 1, but has ranged from over 75%
in 2001 and 2004 to less than 50% in 2002.
Based on current
planting date research, the “normal” optimum planting period for yield
appears to be mid-late April in west Kentucky. Planting earlier or
later than this time period resulted in less than maximum yield. Over
the long-term, planting dates of April 10 to April 30 should achieve
optimum or close to optimum yield potential. To avoid substantial
yield losses, corn planting should be completed by May 1-5 in west
Kentucky. Extrapolating to other areas of the state: corn plantings
should be completed by May 1 in far western Kentucky; by May 5-10 in
west-central Kentucky; and by May 10-15 in eastern Kentucky.
research will tell us what will most likely occur, and not what
actually will occur in any specific year. Many farmers will start
planting as soon as soil moisture conditions allow them to get into
the field. Early planting does have several advantages, as previously
stated. If intentions are to plant early, then consideration should be
given to the risks (less than ideal stands, frost damage, and loss of
potential yield) versus rewards (close to optimum yields and avoiding
the risk of possible weather delays later in the planting season).
This is a decision that farmers face each year. It is probably worth
the risk of starting to plant early (particularly with a large corn
acreage) rather than risk the subsequent chance of poor weather
causing you to finish planting in mid-late May. Yield penalties for
planting too early are usually not as severe as planting too late. By
mid-April, if soil moisture conditions are suitable, soil or air
temperatures should not have as much impact on the decision to begin
planting because of calendar date.
Another aspect of
the planting date research study discussed in this article was to
determine the economical benefit of using a Bt versus a non-Bt hybrid
at each of the planting dates. There are higher seed costs of about
$9-$10/acre associated with a Bt hybrid. The two medium maturity
hybrids used in this study were hybrid isolines (genetically the same
except for the Bt trait). The Bt trait provides resistance to the
European and southwestern corn borer which can cause yield loss damage
to corn in Kentucky. The Bt and non-Bt hybrid yield comparisons are
provided in Table 2.
There was not an
economical yield benefit for the Bt hybrid at the two earliest (April)
planting dates over the 6-year period of the study. The yields of the
Bt and non-Bt hybrids were statistically equivalent. However,
beginning with the early May planting date, there was an economic
yield benefit for planting the Bt hybrid rather than the non-Bt
hybrid. The later the planting date, the greater the yield benefit for
the Bt hybrid. Based on corn borer damage evaluation ratings, the
non-Bt hybrid had more damage than the Bt hybrid, particularly at the
later planting dates. A special thanks to Dr. Ric Bessin and Dr. Doug
Johnson of the Department of Entomology for providing the corn borer
damage evaluations for this study. The results of this study imply
that it would be economically beneficial to plant a Bt hybrid if corn
plantings are made after May 1.
Planting Date Effect on Corn Yield.
Date Range Over
(Bu/Acre)* (Six-year average) (2000-2005)
April (April 22)
• Location =
west Kentucky, (UKREC), (Princeton, Ky.).
two medium maturity hybrids (Bt and non-Bt).
Planting Date Effect on a Bt and Non-Bt Hybrid.
UKREC (Princeton, Ky.).
Hybrid = Pioneer 33G26 (2000-2004) and Pioneer 33R77 (2005).
Bt Hybrid =
Pioneer 33G30 (2000-2004) and Pioneer 33R78 (2005).
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Chad Lee, Plant and Soil Science
publications are now available to help you manage the 2006 corn crop.
Nitrogen Transformation Inhibitors and Controlled Release Urea,
by Greg Schwab and Lloyd Murdock.
Estimating Corn Yields, by Chad Lee and Jim Herbek.
Insecticide Recommendations for Corn – 2006, Ric Bessin and
publications are available online at: www.uky.edu/Ag/GrainCrops/corn.htm.
AGR-185 and AGR-187 are linked under the “Grains Production” heading.
ENT-16 is linked under the “Insects” heading.
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Managing oil and
protein levels in soybean
D.B. Egli and Todd Pfeiffer, Plant
and Soil Sciences
What can farmers
do to produce soybeans with oil and protein levels that are eligible
for the premium prices available in some markets? The short answer is,
unfortunately, not much. Worrying about oil and protein is a new
experience for Kentucky soybean producers. Soybeans are usually sold
by the bushel which makes yield the primary focus, but now seed
composition has moved into the picture in some markets.
negatives that make it difficult to manage oil and protein levels.
There is a negative relationship between oil and protein - as protein
concentration goes up, oil concentration goes down. Yield is another
negative, it usually goes down as protein concentration goes up. These
two negatives make it difficult to combine high yield with high
protein and oil levels.
Oil and protein
levels are influenced by variety and weather, primarily temperature,
during seed filling. Protein levels usually go down as air temperature
goes up (and of course, oil levels go up). Temperature could be
important when comparing regions (North vs. South) or planting dates
(especially double cropped soybeans). Year-to-year variation in
temperature makes it difficult to find clear trends in seed
composition, but in Kentucky, protein levels in double-cropped
soybeans may be a little lower and oil a little higher than soybeans
from conventional production systems, but the difference may be small
and, in some years practically non existent. Drought may also decrease
protein and increase oil levels although this response may be an
indirect effect of the high temperatures that normally come with a
The variety you
grow will also influence oil and protein levels. Plant breeders in the
past simply made sure that oil and protein levels in new varieties
were about the same as the varieties they replaced. Breeding can
increase soybean protein levels, but breeding for higher protein often
reduces yield and oil levels. Some soybean breeders are releasing high
protein varieties for specialty markets, and these novel varieties are
tested in the Kentucky Soybean Performance Tests. Yield and seed
composition data are available to compare the performance of these
varieties with conventional grain varieties, and it is easy to find
evidence of the two negative relationships in these data.
variety’s protein and oil concentration are stable relative to other
varieties. While environmental conditions will move oil and protein
levels up or down, varieties continue to rank in a similar order.
The year will
largely determine whether protein and oil standards are met. For
example, let’s choose a standard of greater than 35.5% protein and
19.2% oil. Only 27 of 133 varieties in the Kentucky Soybean
Performance Tests in 2003 met this standard, while in 2004 it was 54
of 155 (Table 1). In 2005, however, 104 out of 164 surpassed the
standard. The protein and oil genetics of the varieties changed little
during those three years, so it was the weather that caused the
Protein and oil of soybean varieties each year.
that met 35.5% protein and 19.2% oil
relationships between yield, oil and protein may make it difficult to
produce soybeans with high oil and protein concentrations and
exceptional yield. Producers can use the data in the Kentucky Soybean
Performance Tests to evaluate yield and seed composition of the
varieties offered for sale in Kentucky and decide if they can find a
variety that will, first, met the requirements of the buyers and,
secondly, make more money than the best variety without the premium.
recommendation is that you create a list of varieties that meet your
needs for agronomic characteristics: yield, maturity group, SCN
resistance, etc. Then check the oil and protein levels in the Kentucky
Soybean Performance Tests bulletin. Don’t worry about the absolute
protein and oil levels, instead, remove from consideration those
varieties with below average oil percentages. Then select from the
remaining varieties those that have the highest average protein
concentration. This approach should give a variety that has the best
chance at producing acceptable yield and meeting the oil and protein
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