Managing agricultural soils to mitigate CH 4 emission from rice-based cropping systems in China

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

2. Mitigation of CH4 emissions from permanently flooded rice fields is a priority Option 1

3. Crop rotation and management of rice-based agro-ecosystems Apr-Jun Sep-Nov Apr-Jun Non-rice season Rice season Rice season • Double rice crops (Apr-Oct or Nov) • Single rice crop (Jun-Oct or Nov) • Middle rice crop (May-Aug or Sep Non-rice season • Drained and cropped Winter wheat, oil-seed rape…… • Drained and green manure • Fallow • under drained conditions • under flooded conditions

4. 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

5. A kind of rice fields with the largest CH4 emission

6. How to mitigate CH4 emission from permanently flooded rice field?

7. 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

8. 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

9. Temporal variation of CH4 flux during rice growing period Ch-FF Ch-FFR Ch-Wheat Ch-RW

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

11. Temporal variation of CH4 flux during winter season Ch-FF Ch-FFR

12. 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** Correlation coefficient (r value) between CH4 flux and soil temperature in winter season

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

14. Annual CH4 emissions from various treatments of a permanently flooded rice field 100% 67% 36% 33%

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

16. 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

17. Managing paddy soil as dry as possible in winter season is able to mitigate CH4 emission from rice fields Option 2

18. Relationship between soil moisture in the non-rice growing season and CH4 emission during the following rice growing period (greenhouse experiment)

19. Moisture of surface soil in the non-rice growing season was controlled by ground water table in a lysimeter 60 cm 40 cm 20 cm Flooded

20. Relationship between soil moisture in the non-rice growing season and CH4 emission during the following rice growing period (lysimeter experiment)

21. Relationship between soil moisture in the non-rice growing season and CH4 emission during the following rice growing period (field measurement in Chongqing)

22. Field flux measurement sites in China Fengqiu Nanjing Jurong Chongqing Suzhou Yingtan Changsha Guangzhou

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

24. 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.

25. Rotating flooded rice with upland crop(s) would also mitigate CH4 emissions from rice fields during rice growing period Option 3

26. Effect of wet rice and upland crop rotation (Guangzhou) Relative CH4 emission Rice season Upland crop 100% 27% 8%

27. 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

28. Effect of rice straw application time on CH4 emission in wet rice and upland crop rotation system (Greenhouse experiment) Straw application Mean CH4 flux: 4.52 Mean CH4 flux: 3.52 Upland season Rice season Upland season Rice season Mean CH4 flux: 28.6 Mean CH4 flux: 18.3 Upland season Rice season Upland season Rice season

29. Option 4 • Intermittent irrigation (multiple mid-aeration) during rice growing period • Chemical fertilization • Others

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

31. Effect of nitrogen fertilizers on CH4 emission during rice growing period

32. Thank you