Field Plots & Agricultural Research

Dr. Bob Kemerait & Dr. Eric Prostko

University of Georgia

Cooperative Extension Service

April 2001

SAFETY FIRST

Topics

• Demonstration plots vs replicated field trials• Importance of replications• Common experimental designs

– CRD, RCBD, Split-plot, Factorial– Small plots or large plots?

• Plot maintenance• Data analysis & “significance”• Steps for a successful trial

Demonstration Plots

• Objectives– example/information for growers– simple qualitative comparisons

• Advantages– simple to coordinate– simple to assess

• Disadvantages– not very useful for quantitative study– may oversimplify issue

Demonstration Plotsexample: rates of nitrogen on a field crop

HighNitrogen

NormalNitrogen

LowNitrogen

Replicated Field Plots

• Objectives– desire to statistically compare treatments,

varieties, etc.

• Advantages– results recognized by scientific community– results suitable for making decisions

• Disadvantages– more complicated to conduct

Replicated Trialexample: effect of different rates of nitrogen

Block 1 Block 2 Block 3 Block 4

How many replications are enough?

• Generally, the more, the better!– increased “degrees of freedom”– easier to differentiate similar means– better assessment of variation within plot area

• But consider…………– land constraints– time constraints– material constrains – (chemical, plants, etc.)

You want how many reps???!!!!

• Minimum number varies with discipline and researcher

• Absolute minimum: 3 reps

• Foliar fungicide programs: we like to see at least 4 reps

• For soilborne diseases, including nematodes- we like 5 and even 6 reps– uneven distribution of organisms in the soil

Common Types of Experimental Design

• There is more than one type!– all of these designs are replicated

• completely randomized design– appropriate if no variation in plot area

• randomized complete block design– consider ONE source of variation in field!!

• split-plot design– two treatment levels, consider interactions

• factorial design

Completely Randomized Design, 4 reps

Randomized Complete Block, 4 reps

BLK 1

BLK 2

BLK 3

BLK 4

BLK 1 BLK 2 BLK 3 BLK 4

Split-Plot Design

Abound in-furrow

No in-furrow

Abound in-furrow

Abound in-furrow

No in-furrow

No in-furrow

Plot Maintenance

• Importance cannot be overlooked

• Uniformity in planting

• Careful calibration of spray equipment

• Fertility

• Weed control

• Insect control

• Disease control

• Field Tours & PRIDE

Data Analysis

• Statistical analysis can be tricky– consider specialists as references

• Statistical Packages/Software– SAS--------MSTAT--------ARM

• Analysis of Variance– are treatments significantly different?

• Mean Separations– which means are different? – (Fisher’s Protected LSD)

What’s so significant about “significance”?

• Frequent question

• Confusion over meaning

• agricultural standard: 95% (usually)

• “At the 95% confidence level, we can be sure that these means are different at least 95% of the time.”

Getting Started with a Field Trial

• Carefully determine your objectives

• Decide on (limited) treatments

• Develop an experimental design & plot plan

• Secure necessary equipment and materials

• Identify a conscientious cooperator

• Choose your field site CAREFULLY

• Remain safety oriented

• Keep careful notes

• Ask for help

GOOD LUCK!