[R] ANOVA 1 too few degrees of freedom

[Rovinpiper]

I'm running an ANOVA on some data for respiration in a forest. I am having a
problem with my degrees of freedom. For one of my variables I get one fewer
degrees of freedom than I should.

I have 12 plots and I therefore expected 11 degrees of freedom, but instead
I got 10.

Any ideas? 

I have some code and output below:


> class(Combined.Plot)
[1] "character"

> levels(as.factor(Combined.Plot))
 [1] "60m"  "A1"   "B1"   "B3"   "B4"   "C5"   "C9"   "D2"   "D9"   "F60m"
"F8"   "Q7"  

> nlevels(as.factor(Combined.Plot))
[1] 12

> Anova.Trt.D.M.T.Pr.Model <- aov(Combined.Rs~Combined.Trt +
> as.factor(Combined.Plot) + as.factor(Combined.Day) +
> Combined.Trt*as.factor(Combined.Day) +
> Combined.Plot*as.factor(Combined.Day))

Warning message:
In model.matrix.default(mt, mf, contrasts) :
  variable 'Combined.Plot' converted to a factor

> summary(Anova.Trt.D.M.T.Pr.Model)
                                                               Df  Sum Sq   
Mean Sq    F value           Pr(>F) 
   
Combined.Trt                                           1   52.80      
52.805     2.0186e+30  < 2.2e-16 ***
as.factor(Combined.Plot)                         10  677.69    67.769    
2.5907e+30  < 2.2e-16 ***
as.factor(Combined.Day)                         16  2817.47  176.092  
6.7317e+30  < 2.2e-16 ***
Combined.Trt:as.factor(Combined.Day)   16   47.82      2.989      
1.1426e+29  < 2.2e-16 ***
as.factor(Combined.Day):Combined.Plot 160  611.21   3.820 1.4604e+29 <
2.2e-16 ***

Residuals                                                 204    0.00  
0.000                         

---

Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

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