Contribution of fallow periods between rice crops to seasonal GHG emissions: effect of water and tillage management

ABSTRACT

Irrigated rice cultivation is a major source of greenhouse gas (GHG) emissions from agriculture. Methane (CH₄) and nitrous oxide (N₂O) are emitted not only throughout the growing season but also in the fallow period between crops. A study was conducted for two transition periods between rice crops (dry to wet season transition and wet to dry season transition) in the Philippines to investigate the effect of water and tillage management on CH₄ and N₂O emissions as well as on soil nitrate and ammonium. Management treatments between rice crops included (1) continuous flooding (F), (2) soil drying (D), (3) soil drying with aerobic tillage (D + T), and (4) soil drying and wetting (D + W). The static closed chamber method was used to measure CH₄ and N₂O fluxes.

Soil nitrate accumulated and N₂O was emitted in treatments with soil drying. Nitrate disappeared while ammonium gradually increased after the soil was flooded during land preparation, indicating net nitrogen mineralization. N₂O emissions were highest in both transition periods in D + W (437 and 645 µg N₂O m⁻² h⁻¹). Methane emissions were significant in only the F treatment. The highest global warming potential (GWP) in the transition between rice crops occurred in F, with CH₄ contributing almost 100% to the GWP. The GWP from other treatments was lower than F, with about 60–99% of the GWP attributed to N₂O emissions in treatments with soil drying. The GWP in the transition between rice crops represented up to 26% of the total GWP from harvest to harvest. This study demonstrates that the transition period can be an important source of GHG emissions with relative importance of CH₄ and N₂O depending on the soil water regime. Therefore, the transition period should not be disregarded when estimating GHG emissions for rice cropping systems.

KEY WORDS:

• Rice
• fallow
• methane
• nitrous oxide
• soil nitrate

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Corrigendum

Acknowledgments

The Kellogg Company provided support for this research through a grant to IRRI: [Grant Number DPPC-2009-116]. The position of B.O. Sander at IRRI was funded by the Federal Ministry for Economic Cooperation and Development, Germany in 2011–2012: [Grant Number 08.7860.3-001.00]. This work was further supported by the CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS), which is carried out with support from CGIAR Fund Donors and through bilateral funding agreements. For details, please visit https://ccafs.cgiar.org/donors. The views expressed in this document cannot be taken to reflect the official opinions of these organizations. We thank Ms. Sheryll Elaine Rigua and Ms. Elizabeth Gatchalian for assistance with the statistical analyses, Mr. Ceasar Arloo Centeno for assistance with gas analysis, and Mr. Edsel Moscoso for assistance in preparation of some of the figures.

Notes

1. In this study, we have used the GWP values for CH₄ and N₂O as suggested in the 4th IPCC assessment report (IPCC AR4, Forster et al. 2007) because we compare the GHG emissions during the fallow period with emissions during the growth period described by Sander et al. (2014) who also used GWP values of IPCC AR4.

Additional information

Funding

This work was supported by the German Federal Ministry for Economic Cooperation and Development (BMZ): [Grant Number 08.7860.3-001.00];Climate Change, Agriculture and Food Security Program of the CGIAR; The Kellogg Company: [Grant Number DPPC-2009-116].