Plant Growth Modeling: Tools for Analysis and Management

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Plant Growth ModelingTools for Analysis and
Management
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Types of Yield Limiting Factors

• Landscape
• Soil Physical Properties
• Soil Chemical Properties
• Biological Factors
• Man-made Factors
• Weather
• Interactions of the above

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From Fundamentals of Farming and Farm Life by E.
J. Kyle and A. C. Ellis, 1922.
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YLF Interactions

• Single factors are generally less important than
  interactions between factors.
• Crop growth models are increasingly used to
  explain interactions.

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YLF Precision Management?

• Can we measure it?
• Directly or indirectly?
• Is it perennial or sporadic?
• Can we change the factor or respond to it?
• Is managing cost effective?

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Definition
Modeling is the use of mathematical, logical or
experiential relationships to predict the status
of an organism or system in response to changing
conditions.
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Models are used for

• Strategic decisions (what mix of crops to plant)
• Tactical planning (when to spray)
• Logistics (allocation of resources)
• Operational decisions (how much to apply)

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Plant Growth Modeling

• Simple regression
• Multi-variable empirical
• Rule-based
• Mechanistic

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Temporal Variability Focus

• Crop models will be used to understand the
  interactions between crop parameters

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Site-Specific Modeling

• Determining cause and effect on yield variability
  
• Ex Paz, et al, 1998
• Management of temporal variability
• Ex Gossym-Comax

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Why Do Soybean Yields VaryA Case Study of the
McGarvey Field

• Location Perry, Iowa
• 100 grids
• Grid size 0.2 hectare

• Yield, SCN egg count, weeds, soil properties,
  plant population
• Only 77 grids had 3 years of yield data

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Yield Limiting Factors
Soybean Cyst Nematodes (SCN) Weeds Water Stress
Theory exists for modeling SCN and weeds, but
water stress is the unknown factor
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Agronomic Soil Weather
Simulated Annealing
SCN
FLDSKsatRHRF
Crop Model
Set parameter value
RMSEminimized?
Yield
No
Yes
Weed Loss
Yield Optimized Parameters
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McGarvey Field Soybean Calibration
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Yield Potential for 1997
Maximum potential yield
Actual Yield
Difference Water Stress, SCN, weeds
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Turn Water Stress Off
Maximum potential yield
Actual yield
Water StressEffect
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Turn SCN Off
Maximum potential yield
Actual yield
SCN Effect
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Turn Weed Effect Off
Maximum potential yield
Actual yield
Weed Effect
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Estimated Soybean Yield Loss (1997)
Stress Yield Loss kg/ha (bu/ac)
Water Stress 709 (10.7) SCN 119 (
1.8) Weeds 20 ( 0.3) All stress 941 (14.2
) Interactions 93 ( 1.4)
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Gossym-Comax

• Cotton growth model based on plant physiology and
  soil water and chemical processes
• Use of actual and historic weather data provides
  what if scenario evaluation

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Cotton Growth Models

• GOSSYM
• CPM
• Cotton2K
• COTONS