Managing agricultural soils to mitigate CH4 emission from
rice-based cropping systems in China
Zucong Cai
Institute of Soil Science
Chinese Academy of Science
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
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