Table 4: Methane (CH4) and nitrous oxide (N2O) fluxes from a silt-loam soil at the Rice Research and Extension Center near Stuttgart, AR among years (2018 and 2019), tillage [conventional tillage (CT) and no-tillage (NT)], sampling times (1600, 2000, 2400, 0400, 0800, and 1200 hours), and site positions (up-, mid-, down-slope). Reported values are least square means.

Year

Tillage

Time

CH4

N2O

Up

Mid

Down

Up

Mid

Down

 

 

 

___________________________ mg m-2 h-1 ______________________________

2018

NT

1600

0.15* R-W†

0.04* V-Y

2.27 E-K

9.43* A

1.02 B-H

0.08* M-W

 

 

2000

0.17* Q-V

0.03* XY

3.20* D-I

2.85 BC

0.28* G-P

0.01* b-e

 

 

2400

0.10* S-Y

0.25* N-U

2.78 E-J

1.53 B-F

0.34 F-M

0.14* K-S

 

 

400

0.30* M-T

0.08* T-Y

2.34 E-J

0.74 C-I

0.17* I-R

0.02* V-c

 

 

800

< 0.01* Z

0.21* O-U

3.78* C-H

0.37 E-M

0.09* L-V

< 0.01* f

 

 

1200

0.03* W-Y

< 0.01* Z

1.52 F-K

0.41 D-K

0.18* I-R

0.05* S-Y

 

CT

1600

0.48 K-S

0.31* M-T

1.51 F-L

1.61 B-F

3.74* AB

< 0.01* e

 

 

2000

1.32 G-M

0.26* N-U

1.29 G-M

0.32* G-N

1.77 B-D

0.12* L-T

 

 

2400

0.18* Q-V

0.02* Y

1.14 G-N

0.10* L-V

1.25 B-G

0.09* L-V

 

 

400

0.17* Q-V

0.13* S-X

0.64 J-R

0.31* G-O

0.67 C-J

0.01* a-e

 

 

800

0.69 I-R

0.76 I-Q

0.78 I-Q

0.25* H-Q

0.40 E-M

0.03* S-Z

 

 

1200

0.07* T-Y

0.17* Q-V

1.31 G-M

0.36 E-M

0.56 D-J

0.05* S-Y

2019

NT

1600

1.13 G-N

0.31* L-T

35.88* A

0.03* S-a

0.08* M-W

< 0.01* f

 

 

2000

0.31* M-T

0.11* S-X

29.14* AB

0.05* Q-Y

0.03* T-a

0.01* T-d

 

 

2400

0.06* U-Y

0.19* P-V

21.99* AB

< 0.01* c-e

0.02* U-b

0.05* S-Y

 

 

400

2.55 E-J

0.07* T-Y

17.76* A-C

0.01* Z-e

0.02* X-d

< 0.01* f

 

 

800

0.25* N-U

< 0.01* Z

15.49* A-C

0.03* T-b

< 0.01* f

1.70 B-E

 

 

1200

0.03* XY

0.15* R-W

14.39* A-D

0.02* W-d

0.05* S-Y

< 0.01* de

 

CT

1600

0.92 G-P

0.88 H-P

14.40* A-E

0.03* S-a

0.19* I-R

0.09 C-I

 

 

2000

0.06* U-Y

0.02* Y

6.98* C-F

0.03* T-a

0.10* L-V

0.06* O-X

 

 

2400

0.08* T-Y

0.15* R-W

4.25* C-G

< 0.01* e

0.12* L-T

0.03* S-a

 

 

400

0.08* T-Y

0.18* Q-V

2.82 E-J

0.06* P-X

0.12* L-U

0.07* N-X

 

 

800

0.95 G-O

1.02 G-N

1.78 F-K

0.10* L-V

0.11* L-V

0.20* I-R

 

 

1200

0.08* T-Y

0.15* R-W

1.61 F-K

0.06* Q-Y

0.15* J-S

0.03* T-a

† Means across years, tillage, and site positions with different letters are different at P < 0.05. Due to the large number of treatment combinations, letter notations started with a set of capital letters and continued to a set of lower-case letters if necessary. *An asterisk (*) indicates mean value is different than zero (p < 0.05).