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Increased methane emissions from incorporating straw into paddy

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Increased methane emissions from incorporating straw into paddy Powered By Docstoc
					Increased methane emissions from
incorporating straw into paddy fields
outweighs carbon sequestration benefits



Zucong Cai
Institute of Soil Science
Chinese Academy of Sciences
Email: zccai@issas.ac.cn
             Contents

• Background
• Evidences
  – from field experiments
  – from literature data
  – from calculation by IPCC Guidelines
• Conclusion
Straw production in the world
     (Bi et al., 2009, Transactions of the CSAE)


   Straw production: 4.47 Gt/y in the world
                  in 2005
            2.31%
        2.33%
      2.62%                                        China
    2.85%                  18.83%                  USA
                                                   India
    7.17%                                          Brazil
                                                   Argentina
                                                   Indonesia
    10.28%                                         France
                        15.64%                     Russia
 Traditional use   Field burning




Cooking




Animal feed
                    Atmospheric pollution
        General conception on straw
           incorporation into soil

• Sequester carbon into soil
• Improve soil fertility
• Recycle-utilize nutrients, particularly for potassium

• It is a win-win strategy to benefit food security and
  mitigate climate change (Lal, 2004, Science)

• However, it stimulates CH4 emissions from rice fields.

• Question: does it really mitigate climate change?
Locations of two field experiments
Brief descriptions of two sites for field experiment
 • A very old rice field       • An on-going long-term experiment
                                 set up in 1990
 • Location
                               • Location
     31.30N, 119.90E
                                   28.90N, 110.50E
 • Crop system
                               • Crop system
     Summer rice followed by
     winter wheat                  Early rice, late rice, fallow or
                                   green manure in winter
 • CH4 emission
                               CH4 emission
     Low                                High
 • Annual mean temperature     • Annual mean temperature
     15.7C                        16.5C
 • Annual mean precipitation   • Annual mean precipitation
     1177mm                        1448 mm

   Yixing, Jiangsu                   Taoyuan, Hunan
Yixing, Jiangsu   Taoyuan, Hunan
  Field experiment in Yixing, Jiangsu

• The field experiment was supported by the IRRI
  project (IRRIRef. No.: DPPCDPPC200111)
• The treatments were selected for CH4 and N2O
  emission measurements
  – Main treatment: With and without wheat straw
    incorporation
  – Secondary treatment: N application rate at 0, 200, 270
    kg N/ha
  – Wheat straw was incorporated evenly into soils at a
    rate of 3.75 t/ha before rice transplanting
            Treatment in Taoyuan, Hunan
                  N              P                 K
Treatment                                                              Note
              (kg N/ha)     (kg P2O5/ha)      (kg K2O/ha)

   CK            0/0              0/0             0/0     1. Remove all rice straws
                                                             and fallow in winter in CK,
                                                             NP, NK and NPK
   NP        81.3/101.7         90.4/0            0/0
                                                          2. Plant green manure in
   NK        81.3/101.7           0/0         106.6/131.9    winter, which was
                                                             incorporated in situ
                                                             before early rice, in OM
  NPK        81.3/101.7         90.4/0        85.0/153.6
                                                             and HOM
                                                          3. Incorporate in situ all and
   OM        79.3/103.7         90.4/0        85.0/153.6
                                                             half of the early rice
                                                             straw in OM and HOM,
  HOM         52.1/80.0         60.4/0          0/79.5
                                                             respectively

Note: value before “/” for early rice and after “/” for late rice
        Soil organic carbon contents were not changed in
             Yixing by straw incorporation for 3 years

             20
                      No straw    With straw
             16
SOC (g/kg)




             12
                                                     P level from ANOVA
              8                                      analysis
              4
                                                     P for straw effect: 0.954
              0                                      P for N effect:     0.601
                  0           200              270   P for SN:          0.770
                       N application rate


The field is a very old rice field, which SOC content would
have reached equilibrium
        Changes in SOC contents in the long-term
        experiment in Taoyuan from 1990 to 2009

              SOC (g kg-1)    • The rice field was prepared
Treatment                       for rice production in the
             1990     2009      year starting the long-term
   CK        13.3a    18.7a
                                experiment. This might be
                                the reason that SOC
   NP        11.7a    19.5a     increased in all the treatment
   NK        11.4a    18.1a   • Taking NPK as control, bulk
                                density as 1.2 t/m3 in plough
  NPK        13.4a    20.4a     layer (0-18 cm), carbon
  OM         14.6a    27.2b     sequestration was 2.84 and
                                2.07 t CO2-eq/ha/y in OM
  HOM        14.3a    25.3b     and HOM, respectively
  Seasonal CH4 emissions from the treatments in
                Yixing, Jiangsu
                      Seasonal emission
   Treatment                                  Factor   P level
                         (kg CH4/ha)
         N rate
Straw               2003    2004     2005      P-S     0.000
        (kg N/ha)
           0        38.9    50.5      90.3     P-N     0.844
 No
          200       22.7    39.7      66.7     P-Y     0.001
straw
          270       32.7    49.7      78.6    P-SN    0.870
           0        122     244       685     P-SY    0.003
With
straw     200       219     146       659     P-NY    0.974
          270       228     197       829    P-SNY   0.969
 Seasonal CH4 emissions from the treatments in an on-going
              experiment in Taoyuan, Hunan

                Seasonal CH4 emission (kg CH4 ha-1)          Factor    P level
Treat-                                                       Early rice season
           Early rice season          Late rice season
ment
                                                             Treat-
         2007     2008    2009     2007    2008       2009             0.000
                                                             ment
 CK      203      141      194     456     352        516     Year     0.000

 NP      214      150      210     478     495        500     T+Y      0.861

 NK      210      153      213     525     433        410    Late rice season
                                                             Treat-
NPK      279      189      293     549     534        535              0.396
                                                             ment
 OM      351      272      429     862     737        882     Year     0.000

HOM      348      223      412     697     712        844     T+Y      0.951
          Seasonal N2O emissions from the
            treatments in Yixing, Jiangsu
                        Seasonal emission
      Treatment                                Factor   P level
                          (g N2O-N/ha)
           N rate
Straw                 2003    2004     2005     P-S     0.442
          (kg N/ha)
             0        46       45       51      P-N     0.008
  -         200       280     291       105     P-Y     0.142
            270       525     438       183    P-SN    0.921
             0        40       32       20     P-SY    0.991
 +          200       184     174       55     P-NY    0.605
            270       424     434       73    P-SNY   0.996
Seasonal N2O emissions from the treatments in an on-going
             experiment in Taoyuan, Hunan

                Seasonal N2O emission (g N2O-N ha-1)          Factor    P level
Treat-                                                        Early rice season
           Early rice season          Late rice season
ment
                                                              Treat-
         2007      2008    2009    2007    2008        2009             0.253
                                                              ment
 CK      70        -100     220     -37     173        137     Year     0.298

 NP      203       330      183     327     477        600     T+Y      0.561

 NK      203       313      333     413     220        173    Late rice season
                                                              Treat-
NPK       0        210      330     180     73         467              0.257
                                                              ment
 OM      333       467      157     810     460        640     Year     0.000

HOM      77        417      407     430     253        337     T+Y      0.207
                 Calculation

• Global warming potential (GWP)
  – GWP (CO2-eq/ha) =CO2+25CH4+298N2O
  – Emission is defined as positive, sequestration
    as negative
• Net GWP (GWPn)
  – GWPn=GWPs-GWPno
  – GWPs: GWP in the treatment with straw
  – GWPno: GWP in the treatment with no straw
       Net GWP induced by wheat straw
        incorporation in Yixing, Jiangsu
                                  20000
         Net GWP (kg CO2-eq/ha)
                                  18000          N0
                                  16000
                                                 N200
                                  14000
                                                 N270
                                  12000
                                  10000
                                   8000
                                   6000
                                   4000
                                   2000
                                      0
                                          2003          2004   2005
                                                        Year


Straw incorporation induced positive values of GWP, ranged from 3.92,
3.71 and 16.1 t CO2-eq/ha in 2003, 2004, and 2005
Annual GWP in the treatments OM and HOM over
    the treatment NPK in Taoyuan, Hunan

                             14
                             12                        CH4+N2O
      GWP (t CO 2-eq/ha/y)



                             10                        Carbon
                              8                        Net
                              6
                              4
                              2
                              0
                             -2
                             -4
                                  2007   2008   2009     2007    2008   2009

                                            OM                   HOM
Late rice seasonal GWP in the treatments OM and
HOM over the treatment NPK in Taoyuan, Hunan


                             10

                              8                        CH4+N2O
      GWP (t CO 2-eq/ha/y)




                                                       Carbon
                              6
                                                       Net
                              4

                              2

                              0
                             -2

                             -4
                                  2007   2008   2009     2007    2008   2009

                                            OM                   HOM
The relationship between carbon input through straw incorporation and straw-
 induced CH4 and N2O emissions from rice fields in terms of global warming
                 potential (data from literature and this study
         Calculation by IPCC guideline

• On the tier 1 method of the 2006 IPCC Guidelines, CH4
  emission from straw incorporated rice field


         Basline CH 4  (1  Straw amount ) 0.59

• The straw-induced CH4 emission was calculated as:


      Basline CH 4  (1  Straw amount ) 0.59  Baseline CH 4
                                  It is especially important to prevent straw incorporation into
                                        rice fields that have a large baseline CH4 emission

                                           a
                                                                                                                                                 b
                                  7
                                                                                                                                             7                                                      CH4/C sequestration
                                                                                            CH4/C input
                                  6                                                                                                                                                                           0.250
                                                                                                      0.250                                  6
                                                                                                                                                                                                              0.500
  -1
   Straw application rate, t ha




                                                                                                              -1
                                                                                                      0.500                                                                                                   0.750




                                                                                                              Straw application rate, t ha
                                  5                                                                   0.750                                  5                                                                1.00
                                                                                                      1.00                                                                                                    1.25
                                  4                                                                   1.25                                                                                                    1.50
                                                                                                      1.50                                   4                                                                1.75
                                                                                                      1.75                                                                                                    2.00
                                  3                                                                   2.25                                                                                                    2.26
                                                                                                                                             3
                                                                                                      2.75
                                  2
                                                                                                                                             2


                                  1                                                                                                          1

                                      50         100      150      200        250         300                                                        20      30    40    50    60        70   80   90
                                                                         -1          -1                                                                                             -1        -1
                                               Baseline CH4 emission, kg ha season                                                                        Baseline CH4 emission, kg ha season




Ratio of GWP of CH4 emission induced by straw incorporation to straw carbon input (a)
and to straw carbon sequestration, assuming that 35% of added straw C is retained in
soil (b) as a function of baseline methane emission and straw application rate
Singh et al. (2008, Adv. Agron. 98, 117-199)

In the vast majority of cases there was no significant
increase in (rice) yield or profit (from straw incorporation)
                                  Rice yield in Yixing, Jiangsu


                12000                                              Factor   P level
                                         N0
                10000                    N200
Yield (kg/ha)




                 8000                    N270                       P-S     0.324

                 6000                                               P-N     0.000
                 4000
                                                                    P-Y     0.000
                 2000
                                                                   P-SN    0.062
                    0
                        2003 2004 2005      2003 2004 2005         P-SY    0.212
                              No straw          With straw         P-NY    0.013
                                                                  P-SNY   0.367
Averaged yields of early rice and late rice over 2007-2009 in
 the long-term experiment carried out in Taoyuan, Hunan
                         Conclusions
•   Increased CH4 emissions from incorporating straw into paddy
    fields outweighs carbon sequestration benefits in terms of global
    warming potential. Therefore, from the viewpoints of GWP and
    rice yield, straw incorporation before rice transplanting should
    not be encouraged.

•   Incorporating straw into soils in the unflooded off-rice season
    in the rice-based ecosystems allows its decomposition under
    aerobic conditions and stimulates CH4 emission less during the
    succeeding rice growing period. But this option may be less
    effective in cooler regions

•   It is preferable to develop off-site uses of surplus crop straw,
    such as generating electricity, producing biogas, or feeding
    animals

				
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posted:8/8/2011
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