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Biometrical exercise 2 - Answers
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Explain why it was necessary to ensure that all areas of land used for the trial has been treated in exactly the same manner prior to the
trial.
It is necessary to ensure that all areas of land used for the trial had been treated in exactly the same manner prior to the trial to ensure standardisation of conditions. This means that it is easier to assess any difference in yield due to the preplant urea if this is the only thing that is varying.
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Explain why all areas of land used for the trial received identical treatment with the exception of the quantities of urea
applied.
As for question 1, if all areas of land used for the trial received identical treatment with the exception of the quantities of preplant urea applied, then any difference in the yield can be more easily accepted as being the result of the preplant urea. Again this is known as standardisation of conditions.
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What plant nutrient(s) are supplied by urea?
The plant nutrient supplied by urea is nitrogen.
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Construct a table and arrange the results in a meaningful way.
Below is an example of a meaningful table.
| Control (kg) |
Treatment A (kg) |
Treatment B (kg) |
Treatment C (kg) |
|---|---|---|---|
| 107.5 | 110 | 109.3 | 147.7 |
| 102.5 | |||
| 95 | 110.5 | 147.5 | 155 |
| 99 | |||
| 109.5 | 114.5 | 117.5 | 138.9 |
| 103.8 |
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Calculate means for each of the treatments and place them in the table constructed for them with the standard deviations.
Means and standard deviations for Control, Treatments A, B and C.
| Control |
Treatment A |
Treatment B |
Treatment C |
|
|---|---|---|---|---|
| Mean | 102.9 | 111.7 | 124.8 | 147.2 |
| Standard deviation | 5.35 | 2.46 | 20.11 | 8.06 |
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Do you think that it would be a reasonable assumption to expect that increasing the quantity of urea would increase the protein percentage of
the wheat? Explain your answer.
Yes it would be a reasonable assumption to expect that increasing the quantity of urea would increase the protein percentage of wheat, because nitrogen is an essential component of protein. If the quantity of urea supplied to the wheat plants was increased, then nitrogen supplied would be increased, hence protein percentage may be increased
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Suggest some reasons for the use of the control and why controls were positioned as they were in the trial.
The controls were used to obtain production figures for no replant application of urea. This provides production figures for comparison. Also, the control in this trial is used to decrease the border effect. In the border areas of the treatments, the effect of the respective treatment may become hazy due to some overlap or interference of one treatment into another. In this trial the control reduces this effect and so makes the treatmnet yields more meaningful.
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Why were each of the treatments replicated three times?
The treatments were replicated three times for the following reasons:- to reduce the standard deviation and hence improve the precision of the trial
- to allow the results to be accepted with more confidence, and
- to provide an estimate of experimental error.
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The standard deviation has been calculated for each of the treatments and is shown in the table above. Explain why the standard deviation is a
useful statistic.
The standard deviation is a useful statistic because it provides information about how the results varied or spread around the mean. In this trial, the results for Treatment B showed the greatest spread or variation around the mean. This is in contrast with the results for Treatment A which showed the least spread or variation around the mean.
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What evidence do you have that indicates that preplant application of urea affects the yields of wheat?
The evidence that preplant application of urea affects the yields of wheat is that with increasing preplant applications of urea, the yield of wheat increases as shown by the means for the experimental trial.
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What evidence do you have that indicates that preplant application of urea affects the yields of wheat?
It would be necessary to know the cost of the extra urea required to produce the increased yield. This would need to be compared with the extra money received due to the increase in yield. In order to make the use of the preplant urea viable, the extra money received due to the increase in yield would need to exceed the cost incurred due to the preplant urea used.
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What recommendations would you make for further investigation into the effect of preplant application of urea on the yield and protein
percentage of wheat?
Recommendations for further investigation into the effect of preplant application of urea would include:- use in other locations
- use with other varieties of wheat
- use in conjunction with other fertilisers.
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