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 Plots example: rates of nitrogen on a field crop High Nitrogen Normal Nitrogen Low Nitrogen

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 Trial example: effect of different rates of nitrogen Block 1Block 2Block 3Block 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 1BLK 2BLK 3BLK 4

Split-Plot Design Abound in-furrow No in-furrow Abound 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!