Paper finds rice paddy fields are a net source of CO2 to the atmosphere

A paper published in Soil and Tillage Research finds rice paddy fields in China act as a net source of CO2 to the atmosphere, as well as a net source of methane [CH4] and nitrous oxide [N2O]. The paper adds to several other peer-reviewed papers finding various agricultural and ocean sites act as net sources of CO2 rather than sinks as previously thought.

CO2 flux over time. Positive values indicate a net source of CO2 to the atmosphere.

Greenhouse gas emission from direct seeding paddy field under different rice tillage systems in central China

• Shahrear Ahmad^a, b, 1, 
• Chengfang Li^a, b, 1, 
• Guangzhao Dai^a, b, 
• Ming Zhan^a, b, 
• Jinping Wang^a, b,
• Shenggang Pan^a, b, 
• Cougui Cao^a, b, , 

• ^a Key Laboratory of Crop Production, Physiology and Ecology Center of Agriculture Ministry of the People's Republic of China, Huazhong Agricultural University, Wuhan 430070, PR China
• ^b College of Plant Science and Technology, Huazhong Agricultural University, Wuhan 430070, PR China

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Abstract

Agricultural tillage practices play an important role in the production and/or consumption of green house gas (GHG) that contributes substantially to the observed global warming. Central China is one of the world's major rice producing areas but a few studies have tried to characterize the mechanisms of GHG release from rice paddy field and quantify global warming (GWPs) based on GHGs emission on this region. In this study four tillage systems consisting of no-tillage with no fertilizer (NT0), conventional tillage with no fertilizer (CT0), no-tillage with compound fertilizer (NTC) and conventional tillage with compound fertilizer (CTC) applications in rice (Oryza sativa L.) cultivation were compared in terms of the carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) emissions from different tillage systems of the subtropical region of China during the rice growing season in 2008. GWPs based on CO₂, CH₄ and N₂O's cumulative emissions were also compared. Tillage and fertilization had no influence on CO₂ emissions. No-tillage had no effect on N₂O emissions but significantly affected CH₄ emissions. Application of fertilizer significantly affected CH₄ and N₂O emissions. Higher CH₄ emissions and lower N₂O emissions were observed in CTC than in NTC. Cumulative CH₄ emission flux in NTC was 51.68 g CH₄ m⁻² while it was 65.96 g CH₄ m⁻² in CTC, 28% (p < 0.05) higher than that in NTC. Cumulative N₂O emission flux in CTC was 561.00 mg N₂O m⁻², and was 741.71 mg N₂O m⁻² in NTC, 33% (p < 0.05) higher than that in CTC. There was no significant difference in N₂O emissions between NT0 and CT0 systems, but significant in CH₄ emissions. GWP [Global Warming Potential] of CTC was 26011.58 kg CO₂ ha⁻¹, which was 12% higher than that in NTC (23361.3 kg CO₂ ha⁻¹), therefore our findings show that no-tillage system was an effective strategy to reduce GWP from rice paddies in central China and thus can serve as a good agricultural system for environmental conservation.

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