Experimental Design in Agriculture
Name:
CROP 590
First Midterm
Winter 2015
Please show your work!
8 pts
15 pts
1) A plant science student wishes to determine factors that influence the prevalence of
Medusahead (an invasive annnual grass) on rangelands in eastern Oregon. Soil test
results from 20 sites showed a positive correlation between the number of Medusahead
present and naturally occuring levels of soil nitrogen. Can he conclude that high nitrogen
fertility causes an increase in the prevalence of Medusahead? Explain your answer.
2) For each of the three examples below, circle the scenario (type of experiment) that
would favor a larger optimum plot size. In the space on the right, provide a brief
explanation for your choice.
Which will favor a larger plot
size?
Reason(s) for your choice
irrigation treatments
i.)
OR
planting density treatments
fertilizer study on
ii.)
Douglas fir trees OR
a wheat crop
testing site with
iii.)
uniform soil OR
variable soil properties
1
8 pts
3) An agricultural consultant was hired by a chemical company to determine if a new
herbicide that they have developed is safe for use on cabbage and if it effectively
controls important weed species. The consultant conducted a trial and reported that the
new herbicide caused no damage to the cabbage crop and that it effectively controlled
germination of redroot pigweed. However, in subsequent trials conducted by the
company, cabbage plants showed damage symptoms from the herbicide, and
germination of redroot pigweed was not significantly reduced by the herbicide.
In evaluating damage symptoms on cabbage, the consultant appears to have made a
(circle the best option):
a) Type 1 error
b) Type 2 error
In evaluating the effect of the herbicide on redroot pigweed germination, the consultant
appears to have made a (circle the best option):
a) Type 1 error
b) Type 2 error
12 pts
4) You have just been hired by a seed company to evaluate 8 oat cultivars for yield
potential in the Willamette Valley. Last year, the company conducted a similar
experiment using a standard plot size, and obtained a CV for yield of 10%. They would
like to be able to detect differences of 25% of the mean, 80% of the time using an alpha
level of 0.05. You plan to use the standard plot size and a Randomized Complete Block
Design. Will 4 replicates (blocks) be sufficient to attain the precision and power desired
for this experiment?
Hints: There are several ways to solve this problem – look for the easiest way!
You won’t be able to calculate power (1-) directly, but you should be able to answer the
question.
2
15 pts
5) You wish to compare the effects of five soil amendments on growth of strawberries. You
are concerned about possible shading from a row of trees on the west side of the field.
You intend to include three replicates of each treatment in 12 m2 plots. Show how you
would arrange your plots on the field diagram below, taking into consideration what you
know about plot shape and orientation. Explain why you chose this arrangement.
North
15 m
25 m
3
6) Four fertilizer formulations were evaluated for their effects on the yield of corn using a
Completely Randomized Design.
14 pts
a) Fill in the boxes to complete the ANOVA.
As CRD
Source
DF
SS
Total
19
6568
Fertilizer
8 pts
MS
F
1016
b) Based on the results, are there significant differences among the fertilizers at the
 = 0.05 probability level? What is your proof?
(use the tables at the back of this exam)
6 pts
c) Assuming that each treatment (fertilizer formulation) was replicated an equal number
of times, what is the standard error of a treatment mean?
8 pts
d) The mean corn yield of plots that received fertilizer Z is 125 bu/acre. What are the
lower and upper limits of a 95% confidence interval around the mean of Z?
6 pts
7) An experiment is conducted as a Randomized Complete Block Design (RBD). After the
experiment is completed it is determined that the relative efficiency compared to a CRD
is 1.60. Circle the answer below that provides the best interpretation of this result.
a. A CRD would have been 60% more efficient than the RBD
b. A CRD would have been 160% more efficient than the RBD
c. The RBD was 60% more efficient than the CRD
d. The RBD was 160% more efficient than a CRD
4
F Distribution 5% Points
Denominator
Student's t Distribution
Numerator
(2-tailed probability)
df
1
2
3
4
5
6
7
1 161.45 199.50 215.71 224.58 230.16 233.99 236.77
2 18.51 19.00 19.16 19.25 19.30 19.33 19.35
3 10.13
9.55
9.28
9.12
9.01
8.94
8.89
4
7.71
6.94
6.59
6.39
6.26
6.16
6.09
5
6.61
5.79
5.41
5.19
5.05
4.95
4.88
6
5.99
5.14
4.76
4.53
4.39
4.28
4.21
7
5.59
4.74
4.35
4.12
3.97
3.87
3.79
8
5.32
4.46
4.07
3.84
3.69
3.58
3.50
9
5.12
4.26
3.86
3.63
3.48
3.37
3.29
10
4.96
4.10
3.71
3.48
3.33
3.22
3.14
11
4.84
3.98
3.59
3.36
3.20
3.09
3.01
12
4.75
3.89
3.49
3.26
3.11
3.00
2.91
13
4.67
3.81
3.41
3.18
3.03
2.92
2.83
14
4.60
3.74
3.34
3.11
2.96
2.85
2.76
15
4.54
3.68
3.29
3.06
2.90
2.79
2.71
16
4.49
3.63
3.24
3.01
2.85
2.74
2.66
17
4.45
3.59
3.20
2.96
2.81
2.70
2.61
18
4.41
3.55
3.16
2.93
2.77
2.66
2.58
19
4.38
3.52
3.13
2.90
2.74
2.63
2.54
20
4.35
3.49
3.10
2.87
2.71
2.60
2.51
21
4.32
3.47
3.07
2.84
2.68
2.57
2.49
22
4.30
3.44
3.05
2.82
2.66
2.55
2.46
23
4.28
3.42
3.03
2.80
2.64
2.53
2.44
24
4.26
3.40
3.01
2.78
2.62
2.51
2.42
25
4.24
3.39
2.99
2.76
2.60
2.49
2.40
26
4.23
3.37
2.98
2.74
2.59
2.47
2.39
27
4.21
3.35
2.96
2.73
2.57
2.46
2.37
28
4.20
3.34
2.95
2.71
2.56
2.45
2.36
29
4.18
3.33
2.93
2.70
2.55
2.43
2.35
30
4.17
3.32
2.92
2.69
2.53
2.42
2.33
5
df
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
0.4
1.376
1.061
0.978
0.941
0.920
0.906
0.896
0.889
0.883
0.879
0.876
0.873
0.870
0.868
0.866
0.865
0.863
0.862
0.861
0.860
0.859
0.858
0.858
0.857
0.856
0.856
0.855
0.855
0.854
0.854
0.2
0.05
3.078 12.706
1.886 4.303
1.638 3.182
1.533 2.776
1.476 2.571
1.440 2.447
1.415 2.365
1.397 2.306
1.383 2.262
1.372 2.228
1.363 2.201
1.356 2.179
1.350 2.160
1.345 2.145
1.341 2.131
1.337 2.120
1.333 2.110
1.330 2.101
1.328 2.093
1.325 2.086
1.323 2.080
1.321 2.074
1.319 2.069
1.318 2.064
1.316 2.060
1.315 2.056
1.314 2.052
1.313 2.048
1.311 2.045
1.310 2.042