Understanding Factors That Limit
Yield in Corn
R.L. (Bob) Nielsen
Agronomy Dept., Purdue University
West Lafayette, IN 47907-1150
ph. (765) 494-4802
Internet: rnielsen@purdue.edu
http://www.agry.purdue.edu/agronomy/ext/corn/talks/ylf/
Precision Farming: Excitement!
• Color maps are fun to look at!
• Yield monitors are fun to look at!
• Hi-tech wizardry is fun to buy and
vendors love to sell it to you!
• Landlords are impressed!
• Finally, maybe we can finally identify
and correct those problem areas in our
fields once and for all!
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Precision Farming: Tools
• The tools to manage cropland on a sitespecific basis are here or are being
developed rapidly
– Yield monitors
– Grid soil sampling
– Variable rate applicators & seeders
– Portable GPS data recorders
– Software to ‘massage’ the data
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Success With PF Technology
• Will depend on your ability to identify and
manage those yield limiting factors that are
most important in each field.
– Yield maps alone are not sufficient.
– Yield maps can clue you in on where to spend
your diagnostic efforts.
– Proactive, intentional season-long crop
monitoring will be important.
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Yield Limiting Factors (YLFs)
• Crop yields are influenced by vast array of
yield limiting factors (YLF)
– Some influence yield directly
– Some interact with others to influence yield
– Some occur every year, others do not
– Some influence different crops differently
– Weather interacts with most of them
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Major Categories of
Yield-Limiting Factors
•
•
•
•
Weather Stress
Pest Pressures
Soil Characteristics
Management Practices of...
– Farmer
– Consultant
– Applicator
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YLF Categories:
Weather Stress...
Season
Length
Temp.
Rainfall
Humidity
Sunlight
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Bragging Rights For
Top U.S. Corn Yields?
• Which states regularly take top honors for
state average corn yields?
– Surely, the answer must lie within the major
CornBelt states? Yes or no?
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Bragging Rights For Top
U.S. Corn Yields, 1997
150
140
127
133
132
134
120
100
50
USDA est’s as of Nov 1
0
IL
IA
IN
MN
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OH
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Bragging Rights For Top
U.S. Corn Yields, 1997
200
190
140
150
127
133
132
185
175
170
170
134
120
100
50
USDA est’s as of Nov 1
0
IL
IA
IN
MN
NE
OH
WA
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AZ
CA
NM
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Basis for High Corn Yields?
• Many days of high light
intensity
– Little rain
– Few cloudy days
– Little haze
• Warm days +
cool nights
– Less night respiration >>>
less dry matter loss
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YLF Categories:
Pest Pressures...
Diseases
Birds, Deer,
etc.
Weeds
Insects
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YLF Categories:
Soil Characteristics...
Tillage
Fertility
Variability
Moisture
Tilth
Temp.
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E.B. White,
farmer-poet-writer...
“A good farmer is nothing more or
less than a handy man with a
sense of humus.”
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YLF Categories:
Management Practices...
Skills
Timeliness
Hybrid
Cultural
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Cultural Practices...
Plant Date
Harv. Date
Machinery
Adj.
Seeding
Rate
Row
Spacing
Chemical
Appl'n
Stand
Establ.
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Which YLFs Are Most Important?
Tim eliness
Variety
Plt. Date
Rainfall
Last year?
Seeding Rate
Sunlight
Row Spacing
This field?
Hum idity
Stand Establ.
Air Tem p.
Chem ical Appl'n
Next year?
Soil Tem p.
Machinery Adj.
That field?
Moisture
Harv. Date
Fertility
Diseases
Tilth
Insects
Weeds
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‘Perennial’ Yield Limiting Factors
• Some yield limiting factors occur every year
– Soil fertility or pH patterns
– Soil drainage patterns
– Patterns of perennial weed growth
• These can be identified or attacked with sitespecific technology
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‘Sporadic’ Yield Limiting Factors
• Other yield limiting factors occur sporadically
over the years...
– Diseases & insects, even fertility problems are
greatly dependent on weather
• Site-specific technology can help identify
these sporadic problems when they occur,
but not necessarily prevent their
reoccurrence
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Identifying YLFs Is Difficult
• Requires season-long monitoring
– Includes both field observations
and crop diagnostics
– For precision farming, will require
monitoring on site-specific basis
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Identifying YLFs Is Difficult
• Requires season-long monitoring
• Requires good note-taking skills
– You think you’ve got reams of data from the yield
monitor now? Wait until you receive the data
from season-long site-specific crop monitoring!
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Identifying YLFs Is Difficult
• Requires season-long monitoring
• Requires good note-taking skills
• Requires good agronomic skills
– Esp. crop diagnostic skills
– Ability to integrate layers of agronomic
information and relate to yield
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Field Observations &
Crop Diagnostics
• Do your homework!
– Educate yourself.
• Meetings, seminars, demo. plots
• Publications, books, magazines, video
• CD-ROM programs
– Purdue’s Corn Diagnostics CD
• World Wide Web
– Corn Growers Guidebook
http://www.agry.purdue.edu/agronomy/ext/corn/
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Field Observations &
Crop Diagnostics
• Do your homework!
• Use “hired gun” expertise
– Professional crop consultants
– Industry agronomists
– County Extension educators
– University specialists
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Field Observations &
Crop Diagnostics
• Do your homework!
• Use “hired gun” expertise
• Identify and diagnose crop problems as early
as you can, not at the end of the season!
– Postmortem diagnoses are difficult, if not
impossible!
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Examples of Field Observations:
Planting to Emergence...
• Uneven or poor stand establishment
– Hybrid weaknesses?
– Seed zone stresses?
– Insect damage?
– Disease damage?
– Planter problems?
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Examples of Field Observations:
Emergence to Knee-High...
• Uneven plant growth?
– Soil tilth, pests?
• Poor plant color or
vigor?
– Hybrid, fertility?
• Poor weed control?
– Herbicide appl’n?
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Examples of Field Observations:
Knee-High to Tasseling...
• Poor or uneven plant growth?
– Nutrient deficiencies?
– Soil tilth?
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Examples of Field Observations:
Tasseling & Silking...
• Uneven pollination success?
– Heat/moisture stress?
– Insect pests?
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Examples of Field Observations:
Tasseling to Maturity...
• Aborted kernels or malformed ears?
– Nutrient deficiencies?
– Excessive plant populations?
– Leaf disease(s)
– Drought stress
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Examples of Field Observations:
Maturity to Harvest...
• Root and stalk rots?
– Hybrid weaknesses?
– Excessive plant
population?
– Nutrient deficiencies?
– Earlier defoliation?
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Examples of Field Observations:
Harvest...
• Yield variability across field?
– Role of yield monitors
• Excessive harvest losses?
– Hybrid weaknesses?
– Combine
adjustments?
– Grain moisture or
harvest date?
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Beware of the
Hazards of Correlations
• As you gather more and more information
about potential YLFs, be aware that apparent
relationships with yield may simply be
random chance events…...
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Ex. of Hazardous Correlation
• Every single person who ate asparagus prior
to 1865 is now dead, therefore…..
• Eating asparagus is hazardous to your
health!
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Real-Life Example #1
“That patch of foxtail sure cut the yield of those
soybeans.”
Maybe that area of the field was also a low spot
that ponded last spring, killed off some of the
soybean stand, and the foxtail took advantage of
the extra sunlight.
So, stand loss rather than foxtail could have been
the real culprit.
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Real-Life Example #2
“My best yields came from an area with twice
Purdue’s recommended soil K levels.”
Occurred during 1995 drought. Best yielding area
was also low, poorly drained area of field.
So, maybe the yield response was more due to soil
moisture availability differences than to soil
potassium levels?
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Without Season-Long Monitoring, Yield
Map Interpretation Can Be Very
Difficult
Drainage
Soil type
Insect
Disease
Fertility
Prev. crop
Variety
Compaction
etc.
Source: Pioneer Hi-Bred Int’l
http://www.pioneer.com/xweb/usa/txt/restech/precision/i971219.htm
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My Advice?
• Hire a good agronomist
to be your Sherlock
Holmes!
• You’ll need the seasonlong expertise to help
with the Precision
Farming puzzle.
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Precision Farming: Challenge
• It may be that we’ll only be able to fine-tune
our crop production to a limited extent with
site-specific technology
– Identify and correct perennial yield limiting factors
such as soil fertility, pH, drainage
– Identify and attack certain sporadic yield limiting
factors ‘on the go’
• e.g., developing pest or disease problems
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Precision Farming: Challenge
• But, we may be limited when trying to sitespecifically manage those yield limiting
factors that interact heavily with seasonal
weather patterns
– At least, until we can better predict next year’s
weather!
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Let’s Remember...
“Farming is a kind of continual
miracle wrought by the hand of
God.”
– -- Benjamin Franklin
Purdue
Agriculture
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