Agriculture Reference
In-Depth Information
three subplot management practices, and three sub-subplot varieties
(Gomez and Gomez, 1984, p. 139). Table 6.4 indicates the error terms
used for each treatment effect. Notice how the degrees of freedom
for the error terms increases from the main-plot treatments to the
sub-subplot treatments indicating the increased precision and greater
likelihood of identifying differences.
Load the dataset Splitsplitplot.dta into memory. This is a dataset
of rice yields with different levels of nitrogen (0, 50, 80, 110, and
140 kg/ha), different management practices (minimum, optimum,
and intensive), and, finally, three different varieties arranged in a split-
split plot design (Gomez and Gomez, 1984, p. 143). Enter the follow-
ing command as one line in the command window:
anova
yield rep nitro
/
nitro
#
rep manage nitro
#
manage
/
rep
#
manage
|
nitro var nitro
#
var manage
#
var
nitro
#
manage
#
var
This results in the following output:
Number of obs = 135 R-squared = 0.9204
Root MSE = 703.947 Adj R-squared = 0.8222
Source | Partial SS df MS F Prob > F
----------------+-------------------------------------------------
Model | 343808249 74 4646057.42 9.38 0.0000
|
rep | 731994.504 2 365997.252 0.66 0.5439
nitro | 61640821.8 4 15410205.5 27.70 0.0001
nitro#rep | 4451350.68 8 556418.835
----------------+-------------------------------------------------
manage | 42936107 2 21468053.5 82.00 0.0000
nitro#manage | 1102973.26 8 137871.657 0.53 0.8226
rep#manage|nitro | 5236334.81 20 261816.741
----------------+-------------------------------------------------
var | 206013160 2 103006580 207.87 0.0000
nitro#var | 14144506.3 8 1768063.29 3.57 0.0019
manage#var | 3851769.19 4 962942.296 1.94 0.1149
nitro#manage#var| 3699232.07 16 231202.005 0.47 0.9538
|
Residual | 29732489.3 60 495541.489
----------------+-------------------------------------------------
Total | 373540739 134 2787617.45
The results indicate that all three factors (fertilizer, management,
and variety) affected rice yield. In addition, there was a fertilizer
by variety interaction. There was no interaction effect for nitrogen
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