An experiment was performed to assess whether heavy metals accumulate in plants grown in soils amended with sludge and if there is an associated accumulation of those metals in aphids feeding on those plants.6 The data in the accompanying table are cadmium concentrations (in micrograms/kilogram) in plants grown under six different rates of sludge application for three different harvests. The application rates are the treatments, and the three harvests represent blocks of time.
|
Rae
|
I
|
2
|
3
|
|
Control
|
162.1
|
153.7
|
200.4
|
|
1
|
199.8
|
199.6
|
278.2
|
|
2
|
220.0
|
210.7
|
293.8
|
|
3
|
194.4
|
179.0
|
341.1
|
|
4
|
204.3
|
203.7
|
330.2
|
|
5
|
218.9
|
236.1
|
344.2
|
a Is there sufficient evidence to indicate a difference in cadmium accumulation in plants grown in plots subjected to different levels of sludge application? Bound or determine the approximate p-value.
b What would you conclude at the α = .01 significance level?