132 / 172
Table – 2
Analyses of Twelve Fertilizer Samples for Urea by AOAC Method 2003.14
Fertilizer
Sample
Lab ID
Total –N*
% Urea-N
Mean
Std. dev.
Lab 1
Lab 2
1
26-068-03
29.89
12.04
12.45
12.25
0.21
2
26-051-01
28.54
8.63
8.51
8.57
0.06
3
26-068-02
28.44
8.68
8.57
8.63
0.05
4
26-076-07
28.33
8.45
8.45
8.45
0.00
5
26-076-06
28.47
8.58
8.60
8.59
0.01
6
26-076-08
24.95
16.08
15.70
15.89
0.19
7
26-079-01
30.78
12.55
12.70
12.63
0.07
8
26-086-04
30.06
12.56
12.07
12.32
0.25
9
26-103-02
28.01
12.09
11.36
11.73
0.37
10
26-103-03
28.13
6.85
6.83
6.84
0.01
11
26-100-03
26.36
15.55
15.28
15.42
0.14
12
26-010-02
29.87
9.37
9.51
9.44
0.07
Average
X�
10.95
10.84
-
-
Standard Deviation
σ
x
2.97
2.87
-
-
Number of samples
n
12
12
-
-
Variance
σ
2
8.80
8.21
-
-
Pearson Correlation
0.99
-
-
-
-
T Stat
1.30
-
-
-
-
P(T<t) one-tail
0.11
-
-
-
-
t Critical one-tail
1.80
-
-
-
-
P(T<=t) two-tail
0.22
-
-
-
-
T Critical two-tail
2.20
-
-
-
-
*
Note: Total-N includes other forms of nitrogen in addition to unreacted (free) urea
A statistical comparison (Students t-test, df, and, P) indicated that the results from two labs were
statistically similar.
The results for the analyses of the Free and Unreacted urea in these twelve fertilizers by two
independent Labs using AOAC Official Method 2003.14 are shown graphically as well in Figure 2.