Table 2 Significant regression coefficients for trend-surface analysis and coefficients of determination (r2) in SOC and TN, C:N, δ13C, and δ15N from three N fertilization treatments (i.e., NN, LN, and HN) in SG and GG. The regression coefficients are used to describe whether a significant decreasing or increasing trend exist. Details are in Li et al. (2010). *, ** and ***represent significance at P < 0.05, 0.01 and 0.001, respectively.

From: Nitrogen Fertilization Restructured Spatial Patterns of Soil Organic Carbon and Total Nitrogen in Switchgrass and Gamagrass Croplands in Tennessee USA

Crop

Variable

Fertilization

Plot

β0

β1x

β2y

β3x²

β4y²

β5xy

r²

SG

SOC

NN

P1

1.55***

     

0.21

   

P2

1.19**

     

0.25

  

LN

P1

1.33***

     

0.30

   

P2

1.39***

   

−0.05*

 

0.38

  

HN

P1

1.15**

 

0.31*

  

−0.10*

0.44

   

P2

1.83***

     

0.19

 

TN

NN

P1

0.17***

    

0.006*

0.39

   

P2

0.11**

     

0.23

  

LN

P1

0.13***

     

0.33

   

P2

0.14***

     

0.39

  

HN

P1

0.12***

 

0.02**

  

−0.006*

0.50

   

P2

0.17***

     

0.17

 

C:N

NN

P1

8.96***

     

0.14

   

P2

11.0***

     

0.39

  

LN

P1

10.0***

     

0.40

   

P2

10.03***

     

0.23

  

HN

P1

9.38***

    

−0.23*

0.31

   

P2

10.82***

     

0.22

 

δ13C

NN

P1

−21.90***

     

0.15

   

P2

−19.90***

     

0.11

  

LN

P1

−20.02***

     

0.22

   

P2

−19.44***

     

0.52

  

HN

P1

−24.17***

     

0.29

   

P2

−21.41***

     

0.24

 

δ15N

NN

P1

4.02***

 

0.89**

 

−0.12**

 

0.52

   

P2

6.06***

   

−0.17**

 

0.65

  

LN

P1

4.22***

 

0.58*

 

−0.08*

 

0.48

   

P2

4.83***

    

−0.13*

0.68

  

HN

P1

4.43***

 

−0.39**

  

0.10**

0.75

   

P2

3.06***

     

0.11

GG

SOC

NN

P1

1.62***

     

0.28

   

P2

1.58***

     

0.34

  

LN

P1

1.87***

     

0.19

   

P2

2.11***

     

0.46

  

HN

P1

2.07***

     

0.35

   

P2

1.19***

0.65*

    

0.39

 

TN

NN

P1

0.17***

     

0.28

   

P2

0.18***

     

0.41

  

LN

P1

0.17***

 

−0.03*

 

0.003*

 

0.30

   

P2

0.20***

     

0.49

  

HN

P1

0.19***

     

0.41

   

P2

0.14***

     

0.47

 

C:N

NN

P1

9.70***

   

0.11*

 

0.42

   

P2

8.74***

     

0.26

  

LN

P1

10.78***

 

1.10*

 

−0.20**

 

0.40

   

P2

10.71***

     

0.30

  

HN

P1

10.82***

     

0.26

   

P2

8.97***

2.02*

 

−0.60*

  

0.37

 

δ13C

NN

P1

−22.32***

     

0.37

   

P2

−23.33***

     

0.50

  

LN

P1

−20.14***

−1.86**

  

−0.14**

0.28**

0.72

   

P2

−19.35***

 

−1.34***

 

0.14*

 

0.69

  

HN

P1

−20.64***

     

0.38

   

P2

−22.03***

     

0.20

 

δ15N

NN

P1

3.29***

     

0.09

   

P2

2.91***

 

0.45*

 

−0.07*

 

0.44

  

LN

P1

3.58***

1.29*

0.50*

−0.35*

  

0.38

   

P2

5.10***

     

0.25

  

HN

P1

3.65***

     

0.17

   

P2

4.58***

     

0.49

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