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What Gap?
The gap between what's possible and what we accept...the
gap between our potential and our actual...the gap between what our
combine harvests and what some combines have harvested.
Think about it. Narrowing that yield gap is:
But, is there a real yield gap
to be explored and exploited?
You bet, and some data, such as the
Iowa corn data in Figures 1 and 2, suggest it 's getting
larger with each passing season. The yield gap between
average corn growers and Master growers has averaged
over 100 bu/A since 1938 and appears to be increasing
at a rate of 0.56 bu/A/yr. Average Iowa corn yields have
increased at a rate of 1.64 bu/A/yr, but Master grower
yields have increased at a rate of 2.20 bu/A/yr.
The yield gap is not unique to
Iowa or to corn.
Table 1 summarizes verified crop
yields for North America. They clearly illustrate the remarkable
attainable yields of today's genetic material and at the
same time, in striking fashion, reveal the huge gap between
attainable yields and the yields normally harvested.
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| Crop |
Yield |
Location |
Year |
| Alfalfa |
24.1
tons/A |
Arizona |
1982 |
| Barley,
spring |
190
bu/A |
Alberta |
1990 |
| Canola,
spring |
70
bu/A |
Alberta |
1999 |
| Corn |
393.7
bu/A |
Iowa |
1999 |
| Cotton |
5.4
bales/A |
Arizona |
1982 |
| Soybean |
118
bu/A |
New
Jersey |
1983 |
| Wheat,
winter |
205
bu/A |
British
Columbia |
1988 |
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| Table
1. Verifiable record crop yields in North America. |
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Some argue that these record-setters are
just lucky and got all the needed rains that their neighbors
missed, or that they have some "weird " soil
that does not occur anywhere else. However, the facts show
that frequently it 's the same growers who set and break
their own records and that the soil types they do it on
are often the dominant soil types in the area. A good example
is Mr. Francis Childs of Manchester, Iowa. In 1999, he
harvested a verified corn yield of 393.7 bu/A, a new world
record. He has won the non-irrigated class of the Iowa
Master Corn Grower Contest for several years and has done
so on the Kenyon-Clyde-Floyd soil association that comprises
51 percent of the soils in his county. What is unique about
Mr. Childs is his management, not his weather or his soil
type.
So what does it take for an individual
to exploit the yield gap?
In one word, management …in a phrase,
management and long-term dedication. Consider the following
characteristics relative to your own management program and
its potential for producing and sustaining high yields.
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A fundamental planning
process that estimates what the actual attainable yield
levels might be within each field, recognizing existing
controllable limiting factors and their interactions
for the cropping system. That 's a challenge. Producing
high yields often requires on-farm experimentation
in which a yield goal is set that you believe is slightly
out of reach. Then all input levels from seeding rate
to variety selection to fertilizer rates are set assuming
you can attain that yield. As you learn, practices
are applied to whole fields and farms. |
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A focus on timeliness of all operations
and a record keeping system that allows quantification
of what works and what doesn't work. |
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Use of technologies
such as genetically enhanced varieties and site-specific
management to control risk. |
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Long-term dedication to soil improvement,
including physical, chemical, and biological properties.
Individuals who produce top yields seldom do it overnight.
That's because properties such as soil tilth, water
holding capacity, and subsoil characteristics can be
improved, but only over a period of several years. |
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A constant watch for yield limiting
factors and dedication to removal of those that can
be controlled. Insufficient soil fertility is an example
of a controllable limiting factor that can be profitably
removed, given sufficient time. |
Soil fertility programs designed
to narrow the yield gap have a goal of removing the soil
supply of immobile nutrients such as phosphorus (P) and
potassium (K) as potential yield limiting factors.
Nearly all record yields have been
produced with high or very high soil test levels. In
most soils you only need to build soil levels once, so
build-up should be viewed as a capital investment or
a land improvement that can be amortized over many years.
What soil test levels are necessary? The answer starts
with relevant soil test calibration research …relevant
to the soils, tillage practices, rotation, varieties,
and yield levels for your farm. If your management system
differs significantly from that of the calibration research,
required levels could also differ.
Points to consider relevant to
the impact of yield potential on soil test level requirements:
Factors common to high-yield environments
tend to increase crop shoot growth more than root growth,
increasing the amount of nutrient that must be absorbed per
unit of root length present. This would potentially increase
soil test level requirements. Factors known to increase shoot
to root ratios include increasing nitrogen (N) or P levels,
increasing water available to the plant, decreasing light
intensity (as in high populations), and soil temperatures
in the 75 to 85 degrees F range.
Good root development in the subsoil will
often increase the supply of water to the plant, but this
also means that a higher percentage of roots might be growing
in less fertile soil, increasing the need for nutrients
in the surface soil.
If hybrids or varieties with the highest
yield potential direct more of their photosynthate to producing
shoot growth rather than root growth, their soil test level
requirements could be higher.
The fact is that we don 't know what the
minimum soil test levels are for yield levels that extend
beyond the range of our calibration research. However,
one thing is certain. If they do differ from levels required
for typical yields, they won 't be lower.
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