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Conducting Experimental Trials

Conducting Experimental Trials. Gary Palmer. Scientific Method. Formulation of Hypothesis Planning an experiment to objectively test the hypothesis Treatments Experimental design Replication Careful observation and collecting of data from the experiment

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Conducting Experimental Trials

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  1. Conducting Experimental Trials Gary Palmer

  2. Scientific Method • Formulation of Hypothesis • Planning an experiment to objectively test the hypothesis • Treatments • Experimental design • Replication • Careful observation and collecting of data from the experiment • Interpretation of the experimental results

  3. Experiment Treatments • Prowl • Orthene • Ridomil

  4. Experiment

  5. Experiment

  6. Effects of Application of MH by Coarse vs Fine Nozzles on Yield of Burley Tobacco

  7. How many reps are needed? • <3 • 3 • 4 • 5 • 6 • >6 • It depends

  8. Why Replicate? • Treatment is repeated two or more times • In a randomized pattern • Provides an estimate of experimental error • Provides a more precise measurement of treatment effect

  9. How many reps are needed? • Number required • Depends on magnitude of detectable differences desired • 100 lb/a, 200 lb/a, 600 lb/a, ? • Inherent variability of subject matter • CV = Coefficient of Variation • Expressed in %

  10. Inherent variability Coefficient of Variation (CV) • Small Grain (6-8%) • Tobacco yields (16-18%) • Black shank (50-70%) • Johnson grass (30-40%)

  11. Inherent Variability • Actual CV% • Tobacco Location MH Residue • Clayton 44.4 • Reidsville 29.9 • Wheat Location Stand Vigor • Clayton 6.3 55.5 Reidsville 5.3 64.7

  12. Burley Tobacco No-till Variety TrialTaylor Co. – Adam Pike Farm

  13. Burley Tobacco YieldHarrison Co. – Ricci Rowland Farm

  14. How can we increase precision? • The precision of an experiment can always be increased by additional replications • Degree of improvement falls off rapidly as replication increase • Example: To double the precision with which two means can be separated in a trail with four replications, reps would have to increase to 16.

  15. Arrangement of ReplicationsConfounded with fields/soil type Field 1 Field 3 Rep 1 Rep 3 Rep 4 Field 2 Rep 2 Wet Spot

  16. Arrangement of ReplicationsConfounded with soil type Rep 1 Rep 7 Rep 2 Rep 8 Rep 3 Rep 6 Rep 4 Rep 5

  17. Arrangement of TreatmentsRandomized complete Block 1 2 3 4 5 6 7 Rep 7 Rep 2 5 3 6 2 1 7 4 Rep 3 Rep 6 Rep 4 Rep 5

  18. Arrangement of TreatmentsBalanced Incomplete Block Design 1 4 7 2 5 8 3 6 9 1 Blk 1 2 3 REP 2 Blk 4 Blk 5 Blk 6 4 5 6 Blk 2 1 5 9 7 2 6 4 8 3 REP 3 Blk 7 Blk 8 Blk 9 Blk 3 7 8 9 REP 4 REP 1 7 5 3 1 8 6 4 2 9 1 Blk12 Blk 10 Blk 11

  19. Arrangement of TreatmentsUnbalanced Incomplete Block Design 3 5 6 7 Blk 1 1 2 5 7 Blk 3 1 4 6 7 Blk 2 Blk 4 1 2 3 6 2 3 4 7 Blk 5 Blk 6 1 3 4 5 Blk 7 2 4 5 6

  20. Replication Confounded with Time • Not enough growth chambers available?

  21. Simulated Data

  22. Herbicide Treatment

  23. Herbicide Treatment

  24. The Completely Randomized Design • The CRD is the simplest of all designs. • Replications of treatments are assigned completely at random to independent experimental subjects. • Adjacent subjects could potentially have the same treatment.

  25. The Completely Randomized Design • Sample layout: Different colors represent different treatments. There are 4 (1-4) treatments with 4 replications (A-D) each

  26. Experimental Design • Randomized Complete Block Design

  27. Experimental Design • Sampling

  28. Experimental Designs • Factorial • One or more factors in one experiment • Study factors that might make cured tobacco darker • Nitrogen (200, 300, 400 lb/a) • Phosphorus (Low, soil test, high) • Potassium (Low, soil test, high) • Harvest date (3, 4, 5 weeks)

  29. Experimental Designs • Factorial • One or more factors in one experiment • Study factors that might make tobacco darker • Nitrogen (200, 300, 400 lb/a) • Phosphorus (Low, soil test, high) • Potassium (Low, soil test, high) • Harvest date (3, 4, 5 weeks) • 3x3x3x3x4=324 plots • If 4 rows by 30 ft = 3.12 acres

  30. Interpretation • What if plant response to nitrogen changes as potassium rates change? • How do you interpret? • What if plant response to nitrogen changes as harvest date increase and potassium rates decrease? • How do you interpret?

  31. Split-Plot Design • Main plot • Ex. Nitrogen Rate • Least precision • Split Plot • Ex. Harvest Date • Most precision

  32. Split-Plot Design

  33. Yield of Burley Tobacco Varieties with Different Fertility – UK Woodford Co. Farm Nitrogen was applied in the ammonium nitrate form .

  34. Experimental Unit Size • In general, variability decreases as plot size increase. • However, once a certain size is reached the increase in precision falls off rapidly. • Little gain in field plots beyond 0.1 acre • Precision is good at 0.01 to 0.02 for most crop (4 rows by 30-35 ft in tobacco) • Individuals may be used as an experimental unit • Trees, cows, goats, etc.

  35. Experimental Unit Size Covariance Removing variability of some independent variable Difference in beginning weight of cows in test Differences in plant stands

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