Managing agricultural soils to mitigate CH4 emission from

rice-based cropping systems in China

Zucong Cai

Institute of Soil Science

Chinese Academy of Science

Mitigation of CH4 emissions from permanently flooded

rice fields is a priority

Option 1

Crop rotation and management of rice-based agro-ecosystems

Rice season Non-rice season

Apr-JunApr-Jun Sep-Nov

Non-rice season

Drained and cropped

Winter wheat, oil-seed rape……

Drained and green manure

Fallow

under drained conditions

under flooded conditions

Rice season

Double rice crops

(Apr-Oct or Nov)

Single rice crop

(Jun-Oct or Nov)

Middle rice crop

(May-Aug or Sep

Rice fields under fallow and flooded conditions in winter

• Total area: 2.7-4.0 Mha

• Distribution: Mainly in mountainous and hilly area in Southwest China

• Poor drainage conditions

A kind of rice fields with the largest CH4 emission

Seasonal CH4 emission (g CH4 m-2) Site

Drained (A) Flooded (B) A/B

Guangzhou 15.811.7 76.035.4 0.21

Yingtan 90.439.4 158.565.8 0.57

Changsha 55.432.0 103.534.6 0.53

Chongqing 47.824.3 56.122.3 0.85

How to mitigate CH4 emission from permanently flooded rice field?

The experiment was setup in 1990

Research on CH4 emission was conducted in four treatments of the experiment from 1995 to 2000

Experimental farm of China Southwest Agricultural University, Chongqing

Design of field experiment in Chongqing

Rice season Non-rice seasonCh-FF

Ch-FFR

Rice season Winter upland crop

Ch-Wheat

Ch-RW

Winter upland crop

Temporal variation of CH4 flux during rice growing period

0

20

40

60

80

100

120

140

160

CH

4 f

lux

[m

g C

H4 m

-2 h

-1]

1995 200 01999199819971996

a

0

10

20

30

40

50

60

70

80

90

100

CH

4 f

lux

[m

g C

H4

m-2

h-1

]

1995 200019 991 99819971996

b

0

10

20

30

40

50

60

70

80

90

100

CH

4 f

lux

[m

g C

H4 m

-2 h

-1]

1995 200019991 998199719 96

c

0

10

20

30

40

50

60

70

80

90

100

CH

4 f

lux

[m

g C

H4 m

-2 h

-1]

1995 20001999199 8199719 96

d

Ch-FF Ch-FFR

Ch-Wheat Ch-RW

Mean CH4 flux during rice growing period (mg CH4/m2/h)

20.2

31.1b

16.5a

10.0a

18.5ab

31.3b

12.4a

Average

18.019.219.117.91997

14.211.116.024.61999

17.515.820.227.3Mean

18.326.923.555.92000

5.48.411.714.61998

31.624.633.535.61996

ND4.817.215.11995

Ch-RWCh-WheatCh-FFRCh-FFYear

Temporal variation of CH4 flux during winter season

0

20

40

60

80

Year

Flu

x (m

g C

H4 m

-2 h

-1)

0

10

20

30

40

So

il te

mp

era

ture

(C

)CH4 flux Soil temperature

95/96 99/0096

98/996

96/976

0

10

20

30

40

50

Year

Flu

x (m

g C

H4 m

-2 h

-1)

0

10

20

30

40

So

il te

mp

era

ture

(C

)CH4 flux Soil temperature

95/96 99/0096

98/996

96/976

Ch-FF

Ch-FFR

Correlation coefficient (r value) between CH4 flux and soil

temperature in winter season

0.7213**0.6281**1999/00

0.7309**0.6340**1998/99

0.22980.19211996/97

0.6969**0.6296**1995/96

Ch-FFRCh-FFYear

Mean CH4 flux (mg CH4/m2/h) during the winter season

5.0b8.4aAverage

6.18.81999/00

4.912.11998/99

5.28.21996/97

4.04.61995/96

Ch-FFRCh-FFYear

Annual CH4 emissions from various treatments of a permanently flooded

rice field

0

30

60

90

120

150

Ch-FF Ch-FFR Ch-Wheat Ch-RWTreatment

CH 4

em

issi

on (

CH 4

g/m

2)

Winter

Rice

100%

67%

33%36%

There was no significant difference in rice crop yield among the treatment

0

2

4

6

8

10

Ch-FF Ch-FFR Ch-Wheat Ch-RW

Treatment

Ric

e Y

ield

(t/

ha)

Mitigation potential if permanently flooded rice fields were completely drained in non-rice growing season

According to the second soil survey of China, there are 2.52 Mha of gleyic paddy soils, which are permanently flooded.

Using month-mean temperature and the relationship between temperature and CH4 flux to estimate CH4 emissions from gleyic paddy soils by province

CH4 emission from gleyic paddy soils in China is estimated to be 0.78 Tg CH4 during the non-rice growing season

Managing paddy soil as dry as possible in winter

season is able to mitigate CH4 emission from rice

fields

Option 2

Relationship between soil moisture in the non-rice growing season and CH4 emission during the following

rice growing period (greenhouse experiment)

0

5

10

15

20

25

30

25-35 50-60 75-85 107

Soil moisture, WHC

Mea

n C

H4

flux

(mg

CH

4/m

2 /h)

Yingtan

Wuxi

Moisture of surface soil in the non-rice growing season was controlled by ground water table in a lysimeter

60 cm40 cm

20 cm

Flooded

Relationship between soil moisture in the non-rice growing season and CH4 emission during the following rice gr

owing period (lysimeter experiment)

Ground water, cm

98/99 soil moisture

g/g

Mean CH4 flux

mg CH4/m2/h

99/00 soil moisture g/

g

Mean CH4 flux

mg CH4/m2/h

60 260 5.76 262 7.64

40 279 6.81 277 11.8

20 294 12.1 305 13.4

Flooding 32.7 46.0

Relationship between soil moisture in the non-rice growing season and CH4 emission during the following rice gr

owing period (field measurement in Chongqing)

y = 0.0664x - 20.271

R2 = 0.5593

0

10

20

30

40

50

60

350 550 750 950

Soil moisture (g/kg)

Me

an

CH

4 flu

x (m

g C

H4/m

2 /h)

Field flux measurement sites in China

Fengqiu

Nanjing

Jurong

Suzhou

Yingtan

Changsha

Guangzhou

Chongqing

CH4 emissions measured across China could be described by the soil moisture in the non-rice

growing season

y = 0. 2848e0. 0851x

R2 = 0. 885

0

20

40

60

80

100

10 20 30 40 50 60 70 80

Si mul ated soi l moi sture %WFPS

CH 4

em

issi

on, g

CH

4 m

-2

• At the national scale, precipitation would be a dominant factor controlling regional variation of soil moisture in the non-rice growing period.

• But to a certain rice field, soil moisture in the non-rice growing period is dependent up topography and management.

• Managing rice fields well-drained, avoiding waterlogged, and making soil moisture as low as possible in the non-rice growing season would mitigate CH4 emission during the following rice growing period.

Rotating flooded rice with upland crop(s) would also mitigate CH4 emissions from rice fields during rice gro

wing period

Option 3

Effect of wet rice and upland crop rotation (Guangzhou)

Rice season

27%

8%

Upland crop 100%

Relative CH4 emission

Application of organic manure at the start of upland crop season instead of before rice transplanting significantly decreases CH4 emission during the rice growing period

Compost before application of organic manure would also reduce the stimulation effect of organic manure on CH4 emission

Option 4

Effect of rice straw application time on CH4 emission in wet rice and upland crop rotation

system (Greenhouse experiment)

Upland season Rice season

Upland season Upland season

Upland season

Rice season

Rice season

Rice season

Straw application Mean CH4

flux: 4.52Mean CH4 flux: 3.52

Mean CH4 flux: 18.3

Mean CH4 flux: 28.6

Option 4

• Intermittent irrigation (multiple mid-aeration) during rice growing period

• Chemical fertilization

• Others

Comparisons of CH4 emissions between intermittent flooding (IF) and continuous flooding (CF) during rice growing period averaged over available data in China

Rice seasonMean CH4 flux, mg CH4/m2/h

IF CF IF/CF, %

Early rice 10.9 10.1 108

Middle rice 5.3 12.8 41

Late rice 12.4 19.2 65

Effect of nitrogen fertilizers on CH4 emission during rice growing period

Rate

kg N/ha

Mean CH4 flux

mg CH4/m2/h

Mean N2O flux

g N/m2/h

Urea (NH4)2SO4 Urea (NH4)2SO4

0 3.31 5.1

100 3.07 1.91 6.3 6.5

300 2.85 1.34 23.0 36.5