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					Managing agricultural soils to
 mitigate CH4 emission from
rice-based cropping systems
           in China
             Zucong Cai
      Institute of Soil Science
    Chinese Academy of Science
Option 1


Mitigation of CH4 emissions
 from permanently flooded
   rice fields is a priority
 Crop rotation and management
 of rice-based agro-ecosystems
Apr-Jun               Sep-Nov                        Apr-Jun
       Rice season                 Non-rice season

 Rice season             Non-rice season
 Double rice crops      Drained and cropped
  (Apr-Oct or Nov)         Winter wheat, oil-seed rape……
 Single rice crop       Drained and green manure
  (Jun-Oct or Nov)       Fallow
 Middle rice crop          under drained conditions
  (May-Aug or Sep           under flooded conditions
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
Site          Seasonal CH4 emission (g CH4 m-2)

            Drained (A)   Flooded (B)      A/B

Guangzhou   15.811.7      76.035.4       0.21

Yingtan     90.439.4      158.565.8      0.57

Changsha    55.432.0      103.534.6      0.53

Chongqing   47.824.3      56.122.3       0.85
How to mitigate CH4 emission
 from permanently flooded
 rice field?
Experimental farm of China
Southwest Agricultural University,
Chongqing


The experiment was setup in 1990



                            

 Research on CH4 emission was conducted in
 four treatments of the experiment from 1995
 to 2000
        Design of field experiment in Chongqing
                Rice season        Non-rice season
Ch-FF



Ch-FFR


              Rice season     Winter upland crop
Ch-Wheat

                              Winter upland crop
Ch-RW
Temporal variation of CH4 flux during
       rice growing period
                             16 0                                                                             10 0

                             14 0                                                                              90    b
                                    a

                                        Ch-FF                                                                  80
                                                                                                                                           Ch-FFR
 CH 4 f lux [m g CH4 m h ]




                                                                                  CH4 f lux [m g CH 4 m h ]
-1




                                                                                 -1
                             12 0
                                                                                                               70
-2




                                                                                 -2
                             10 0
                                                                                                               60
                              80                                                                               50
                                                                                                               40
                              60
                                                                                                               30
                              40
                                                                                                               20
                              20                                                                               10
                               0                                                                                0
                                    1995   1996    1997   1998    1999   200 0                                       1995   1996    1997    1 998   19 99   2000




                             10 0                                                                             10 0

                              90    c                                                                          90    d

                              80
                                        Ch-Wheat                                  CH 4 f lux [m g CH4 m h ]
                                                                                                               80
                                                                                                                                      Ch-RW
 CH4 f lux [m g CH4 m h ]




                                                                                 -1
-1




                              70                                                                               70
                                                                                 -2
-2




                              60                                                                               60
                              50                                                                               50
                              40                                                                               40
                              30                                                                               30
                              20                                                                               20
                              10                                                                               10
                               0                                                                                0
                                    1995   19 96   1997   1 998   1999   2000                                        1995   19 96   1997    199 8   1999    2000
  Mean CH4 flux during rice
growing period (mg CH4/m2/h)
Year   Ch-FF   Ch-FFR   Ch-Wheat   Ch-RW   Average

1995   15.1     17.2      4.8       ND      12.4a

1996   35.6     33.5      24.6      31.6    31.3b

1997   17.9     19.1      19.2      18.0   18.5ab

1998   14.6     11.7      8.4       5.4     10.0a

1999   24.6     16.0      11.1      14.2    16.5a

2000   55.9     23.5      26.9      18.3    31.1b
Mean   27.3     20.2      15.8      17.5    20.2
Temporal variation of CH4 flux during
          winter season
                                        80                                                  40




                                                                                                 Soil temperature (C)
                                                                 CH4 flux

      Flux (mg CH m-2 h-1)
                 4
                                        60
                                                                 Soil temperature
                                                                                            30                          Ch-FF
                                        40                                                  20

                                        20                                                  10

                                         0                                                  0
                                                 95/96   96/97       98/99          99/00
                                                         6           6              96
                                                                    Year
                                         50                                                 40
                                                                                                                        Ch-FFR



                                                                                                 Soil temperature (C)
                                                                 CH4 flux
                -1
                    Flux (mg CH m h )




                                         40                      Soil temperature
                                                                                            30
                -2




                                         30
                               4




                                                                                            20
                                         20
                                                                                            10
                                         10

                                             0                                              0
                                                 95/96   96/97       98/99          99/00
                                                         6           6              96
                                                                    Year
Correlation coefficient (r value)
   between CH4 flux and soil
 temperature in winter season
 Year         Ch-FF        Ch-FFR

1995/96      0.6296**      0.6969**

1996/97       0.1921       0.2298

1998/99      0.6340**      0.7309**

1999/00      0.6281**      0.7213**
Mean CH4 flux (mg CH4/m2/h) during
       the winter season

  Year        Ch-FF      Ch-FFR
 1995/96       4.6         4.0
 1996/97       8.2         5.2
 1998/99      12.1         4.9
 1999/00       8.8         6.1
 Average      8.4a        5.0b
Annual CH4 emissions from various
treatments of a permanently flooded
              rice field
                         150

                               100%                                    Winter
                         120
CH4 emission (CH g/m2)




                                                                       Rice

                                       67%
               4




                         90


                         60                                                     36%
                                                            33%
                         30


                          0
                               Ch-FF   Ch-FFR               Ch-Wheat            Ch-RW
                                                Treatment
There was no significant difference in
 rice crop yield among the treatment

                     10

                     8
 Rice Yield (t/ha)




                     6

                     4

                     2

                     0
                          Ch-FF   Ch-FFR      Ch-Wheat   Ch-RW
                                       Treatment
  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
Option 2


Managing paddy soil as dry
   as possible in winter
 season is able to mitigate
  CH4 emission from rice
           fields
  Relationship between soil moisture in the non-rice
growing season and CH4 emission during the following
    rice growing period (greenhouse experiment)

                                 30
   Mean CH4 flux (mg CH4/m2/h)




                                 25       Yingtan
                                          Wuxi
                                 20

                                 15

                                 10

                                 5

                                 0
                                      25-35         50-60          75-85   107
                                                     Soil moisture, WHC
Moisture of surface soil in the non-rice growing season
was controlled by ground water table in a lysimeter




                                 20 cm
                   40 cm
     60 cm
                                             Flooded
    Relationship between soil moisture in the non-rice
  growing season and CH4 emission during the following
        rice growing period (lysimeter experiment)
Ground      98/99 soil   Mean CH4 flux   99/00 soil   Mean CH4 flux
water, cm   moisture     mg CH4/m2/h     moisture     mg CH4/m2/h
               g/g                          g/g

   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 growing period (field measurement in Chongqing)
   Mean CH flux (mg CH/m2/h)


                               60
                               50         y = 0.0664x - 20.271
                     4




                               40              R2 = 0.5593

                               30
                               20
          4




                               10
                                0
                                    350        550               750   950
                                                Soil moisture (g/kg)
Field flux measurement sites in China


                  Fengqiu


                               Nanjing

          Chongqing                Jurong
                                     Suzhou
                              Yingtan

                               Changsha

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

                      100
  -2
  m    4




                      80                  y = 0. 2848e
                                                      0. 0851x
  CH emission, g CH




                                              2
                      60                     R = 0. 885

                      40

                      20
    4




                       0
                            10   20      30      40       50     60      70   80
                                          ul            oi        W
                                      Si m at ed soi l m st ur e % FPS
• 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.
Option 3


 Rotating flooded rice with
upland crop(s) would also
  mitigate CH4 emissions
from rice fields during rice
      growing period
 Effect of wet rice and upland
  crop rotation (Guangzhou)
                      Relative CH4 emission

Rice season     Upland crop      100%



                                  27%



                                   8%
Option 4

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
     Effect of rice straw application time on CH4
    emission in wet rice and upland crop rotation
          system (Greenhouse experiment)
Straw
application    Mean CH4                   Mean CH4
               flux: 4.52                 flux: 3.52
  Upland season Rice season Upland season Rice season


                Mean CH4                  Mean CH4
                flux: 18.3                flux: 28.6
  Upland season Rice season Upland season Rice season
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

                    Mean CH4 flux, mg CH4/m2/h
Rice season
                       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    Mean CH4 flux  Mean N2O flux
kg N/ha mg CH4/m2/h    mg 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

				
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