Lloyd Murdock, Plant and Soil
Fields rutted by
wheel tracks during soybean harvest are a common sight in the grain
producing areas of Kentucky. The ruts look bad but may not be as
damaging as they look.
combines can compact soil, the physical condition of the soil must be
right for compaction to be severe. When soils are dry enough that they
could be tilled properly, little compaction is likely to occur because
shear strength of soil is great enough to withstand the pressure. This
is the usual condition under which we harvest.
As the soil
becomes wetter, they are easier to compact because the soil aggregates
and individual particles become lubricated with water which reduces
the shear strength. The large pores are filled with air and the small
ones filled with water. The large pores collapse with pressure and
compaction is formed. Compacted ruts are formed.
As the soils
become wetter, all pores are filled with water and the soils can not
be compacted but the shear strength of the soil is reduced to near
zero. This causes large, deep, muddy ruts with little or no
So there are two
kinds of ruts, compacted and uncompacted. Both of these can exist in
the same field.
These look the
worst and have large raised ridges on each side of the track. There is
a lot of mud. There is no compaction in these ruts or a small amount
at the bottom of the rut. The soil structure was damaged but can be
The rutted areas
need to be smoothed for future production. No-tillage helps
reestablish the soil structure. The ruts can be smoothed two ways. One
is with a roller (such as a rice roller) when the soil is still
saturated. The soil moves back into place and the saturated soils
prevent any compaction from the process. It does negatively affect the
structure but can be quickly corrected. For most people, it will
require waiting until the area has dried and using surface tillage to
fill and smooth the ruts.
These ruts don’t
look too bad. They have little or no lip on the rut and are mostly a
compressed track. In these ruts the compacted zone usually starts 1 to
2 inches below the bottom of the rut and is compacted for several
inches. The depth of the compaction can range from 4 to 10 inches.
Compaction can also be severe and deep on the ends of edges of the
fields where grain hauling was done. These areas may need special
The amount and
depth of compaction can easily be checked by probing with a
penetrometer, ½ to ¾ inch steel rod or long screwdriver. When pushed
into the soil, the compaction can be easily felt by resistance. With
this information (depth and amount of compaction), you can select the
tillage tool needed for repair.
The rutted areas
need to be smoothed and the compaction area broken. If the bottom of
the compacted layer ends within 8 to 9 inches of the soil surface then
a tillage tool such as a chisel plow could be used. For deeper
compaction, a subsoiler would need to be used. If only the top 6
inches of soil was tilled to remove the compaction and the compaction
below 6 inches remains, the area would produce 80 to 85% of its
If we get too
anxious about this tillage in the spring, we could cause additional
compaction. Compaction caused by spring tillage of wet soils can be
severe and more costly than that caused by the combine at harvest. Any
time soils are tilled wet, the potential for serious compaction
exists. It is important that we wait for the soils to dry enough for
proper tillage and shattering.
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Record Yields –
What Have We Learned?
D.B. Egli and Chad Lee, Plant and
The year 2006
produced another record soybean yield. A farmer in Southwest Missouri
produced 139 bushels per acre to win the Missouri Soybean Association
Yield Contest. What can we learn from this farmer’s accomplishment
that will increase the yields of all farmers? What have we learned
from record yields in the past?
Farmers are no
different from anyone else – they like to brag about their
accomplishments. If you don’t believe that, just visit a small-town
coffee shop before 7:30 AM on a weekday. In fact, it is easy to
imagine one of the first farmers bragging to his neighbor about his
high yields 10,000 years ago when people stopped gathering their food
supply from what was available and began planting and harvesting
crops. The record yield syndrome in soybean is not new.
In the mid -
1960’s a farmer won the Illinois soybean yield contest with 82.7
bushels per acre. A few years later farmers in Missouri, Indiana,
Nebraska and Illinois topped a national yield contest sponsored by a
chemical company with yields above 100 bushels per acre. Winning
yields from state contests in Iowa, Nebraska and Missouri were often
in the 80 bushel range (one irrigated contest approached 100 bushels
per acre) in the late 1990s according to a summary by Jim Specht (a
soybean researcher at the University of Nebraska) and his co-authors
in the journal Crop Science. They also reported that two
scientists equaled or exceeded 100 bushels per acre in their research
plots in the mid - 1980s. The record quoted by Lloyd Evans in his 1993
Crop Physiology book is 110 bushels per acre. The record average state
yield in the US is 52.5 bushels per acre (2005 in Iowa, an average for
10 million acres) which is higher than the Kentucky record (45 bushels
per acre in 2006 from 1.36 million acres).
What have we
learned from these record yields? On one hand the answer is not much
because we haven’t found a “silver bullet” that will produce high
yields on all farms in Kentucky. On the other hand, we have learned
that it is the tried and true recommended management practices that
provide the foundation for record yields. Close analysis of many
record yields often reveals that the farmer simply followed
recommended best management practices.
several years of record yields in experimental plots in New Jersey
(five year average of 103 bushels per acre) were attributed to high
yielding, lodging resistant varieties; high quality planting seed;
well drained, fertile soil (adequate levels of micro- and
macro-nutrients); firm seedbed and precision planting; optimum soil
moisture conditions throughout the growing season (irrigated if
needed); control of weeds, diseases and insects; minimizing harvest
losses; and doing everything on time.
In Kentucky we
would probably add the use of cyst nematode resistant varieties and
crop rotations to this list. There is certainly nothing radically new
on this list, no practices that good farmers are not already using.
The value of these practices is backed by years of research and
experience through out the soybean belt. We know that they work and
are essential, but no one would feel confident that these practices
(even when rain is guaranteed with irrigation) would always produce
record yields in excess of 90 to 100 bushels per acre.
Zeroing in on the
cause of record yields is difficult. In fact, there is often debate
about whether record yields are even real. Is it possible to produce
soybean yields well in excess of 100 bushels per acre? Many Crop
Physiologists and Agronomists would probably say no, but others in the
soybean business would surely disagree. This debate is fueled by the
failure to find clear reasons for the records. Key measurements, such
as seed size (weight per seed or seeds per pound), the number of pods
per unit area and key growth stages, could help determine the cause of
the high yield. These measurements require extra effort and are not
often made in yield contests, and, there is no guarantee that they
would help pinpoint what aspect(s) of the plant, the soil or the
environment triggered the record. Causes are hard to find, especially
when the record occurs only in a single field surrounded by fields
with normal yields.
yields and searching for the silver bullet has not, in our opinion,
added very much to soybean yields in Kentucky. If producers
concentrate on the silver bullet and don’t pay enough attention to
best management practices, yields could be reduced. It is not easy to
apply best management practices to all of your production – it
requires a lot of planning and paying attention to detail (and maybe a
little luck with equipment and weather), leaving little room for
distractions by silver bullets and records.
What have we
learned from record yields? We have learned that there is no silver
bullet that you can apply in your fields next year – focusing on the
best management practices gives you the best odds for high yields. The
challenge is to get it done, and then the rest depends on the weather.
We cannot neglect best management practices in our search for high
yield; remember that “facts do not cease to exist because they are
ignored” (Aldous Huxley).
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Chad Lee, Plant and Soil Sciences
The top three
yields from non-irrigated fields in the Kentucky Corn Contest for 2006
were 274.05, 256.32 and 253.41 bushels per acre. The Schwenke Brothers
of Boone County, James C. Bickett/Bickett Farms in Muhlenburg County
and John Martin/Martin Farms in Todd County placed 1st, 2nd,
and 3rd, respectively.
Brothers placed 2nd in the nation in the National Corn
Growers Association Corn Contest in the “A-No Till/Strip Till
Non-Irrigated” division. Seven Springs Farms in Trigg County received
2nd and 3rd place in the nation in the
“A-Non-Irrigated” division with yields of 277.7896 and 272.9541 bu/acre.
These two entries were received late for the Kentucky contest,
preventing them from winning awards.
Brothers and John Martin both planted corn into 30-inch rows in
no-till conditions following soybean. Seven Springs Farms planted corn
in 20-inch rows in a minimum tillage situation and sprayed Headline
fungicide. Older research at the University of Kentucky shows greater
disease problems in 20-inch rows.
applied a range of 0.75 to 1.0 pound of nitrogen per bushel of corn.
We often hear about Midwest recommendations of applying 1.2 pounds of
nitrogen to get one bushel of corn. Under good growing conditions on
well-drained soils, we can use less nitrogen in Kentucky.
None of these
farmers used a magical potion to get high yields. Several of these
farmers do not have “contest fields”. These farmers were blessed with
good soils and timely rains, and they paid attention to the
fundamentals of growing corn. Some of those fundamentals included
selecting good hybrids, planting on time, establishing a good stand,
applying adequate fertilizer, providing excellent weed control,
applying additional pest management where needed, and harvesting on
time. In addition to all of this, each was willing to take a day or
two from their harvest schedule to harvest corn for a yield contest.
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Corn and Soybean
Yield Ratios – What Should we Expect in 2007?
D.B. Egli, Plant and Soil Sciences
Which crop will
make the largest profit in 2007 – corn or soybean? The answer depends
in large part on the relative yield of the two crops. We know corn
yield is always higher than soybean, but the question is – how much
higher and how much does the ratio vary?
To answer these
questions I calculated the ratio of corn and soybean yield for each
year from 1950 through 2005. The ratio started at about 2.0 in 1950
and it increased to about 3.1 in 1980 (Figure 1). The yields in 1950
were 37.0 bushels per acre for corn and 17.5 bushels per acre for
soybean, giving a ratio of 2.1. The ratio increased because corn yield
increased faster than soybean yield during this period, probably
Ratio of corn
and soybean yield in Kentucky, 1950 to 2003. The ratio was
calculated using yield data (bushels per acre) from the National
Agricultural Statistics website (http://www.nass.usda.gov/index.asp).
Ratio of corn and soybean yield in three Kentucky counties, 1972
to 2005. Yield data (bushels per acre) from the National
Agricultural Statistics Service.
as a result
of improved hybrids, higher N rates and plant populations, and
better weed control options.
there has been no trend, up or down, in the ratio since 1982; it
just fluctuated around an average of 3.3. There was no trend in
the ratio during this period because corn and soybean yields were
increasing at the same relative rate. I also looked at
corn/soybean ratios in Iowa, Illinois, Indiana, Tennessee, and
Missouri and they also showed no trend for the past 20 or so
years. The average ratio varied from 3.1 to 3.5. All this means
that corn and soybean yields are increasing at the same relative
rates in all of these states.
varied a lot from year-to-year in Kentucky (Figure 1) and in the
other states. A lot of the variation may be related to which crop
got timely rains during flowering, seed set and seed filling in a
particular year. The highest ratio in Kentucky was 5.0 in 1999
(see Figure 1) when soybean yields were low (21.0 bushels per acre
compared with 105 bushels per acre for corn). On the other hand,
the lowest ratio since 1980 was 2.7; a result of a low corn yield
(89 bushels per acre) and relatively high soybean yield (32.5
bushels per acre) in 1991. In the 25 years since 1980 the
statewide ratio was never less than 2.7 and it was above 3.5 for
only five years.
calculated ratios for some counties in Kentucky. The variation for
Christian and Calloway counties was larger than at the state
level, but the variation in Union county was
Figure 2 with Figure 1). Counties with lower yields, on the average,
(Christian and Calloway counties) seemed to show more variation in the
ratio than counties with higher yields (Union county).
In fact, the
ratio in Union county was almost always between 2.5 and 3.5 but in
Calloway and Christian counties it was often above 3.5 with some of
the ratios approaching 10 in 1999, reflecting exceptionally low
soybean yield. The average ratio for the last 20 years (1986 to 2005)
in Union county was 3.2 vs. 3.6 for Calloway county (3.4 ignoring the
unusually high ratio in 1999). The average ratio in Christian county,
where soybean is commonly double-cropped behind wheat, was 3.7 (when
the abnormally high ratio in 1999 was excluded), the highest ratio of
any county, probably reflecting the lower soybean yields typically
associated with double cropping.
What have we
learned from looking at these corn/soybean yield ratios? Most years
the ratio was above 3.0 at the state and county level and it was
usually below 4.0, with some exceptions. The year-to-year variation in
the ratio was pretty large, unfortunately, and it’s not predictable.
This is nothing new for farming where every crop involves a gamble
with the weather. You have a choice when planning for your 2007 crop,
you can gamble by assuming a high or a low ratio and hope that you
guessed right. Or you can take a more traditional approach and
minimize the gamble by assuming an average ratio (3.3 for example) and
avoiding the extremes.
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