Scientists reveal agricultural practices increase CH4 and N2O production

A research team from the Chinese Academy of Sciences (CAS) has discovered that with appropriate agricultural management, Methane (CH4) and Nitrous Oxide (N2O) production in paddy fields is decreased under elevated Carbon Dioxide (CO2).

CAS noted that the inevitable rise of atmospheric CO2 concentration plays an important role in regulating carbon and nitrogen cycling in the rice-cropping system. Illuminating the impact of elevated CO2 concentration (ECO2) on CH4 and N2O emissions from paddy fields is crucial for assessing the agricultural production response to climate change.

How was this data collected?

This study was led by Dr Guangbin Zhang, Jing Ma, and Hua Xu, from Institute of Soil Science, Chinese Academy of Sciences. Data extraction was conducted by Haiyang Yu, Tianyu Wang, Qiong Huang, and Kaifu Song, also from the Institute of Soil Science, Chinese Academy of Sciences.

The team analysed 175 independent observations that consisted of 112 groups of CH4, and 63 groups of N2O; this involved considering study sites and agricultural management.

What did the results reveal regarding CH4 and N2O production?

The team found that elevated CO2 (ECO2) considerably increased CH4 emissions from rice fields by 23%, but it reduced N2O emissions by 22%. A longer duration of ECO2 (≧10 years), ECO2 significantly reduced CH4 and N2O emissions by 27% and 53%, respectively.

Along with the increasing levels of ECO2, the stimulating effect of ECO2 on CH4 emissions showed a trend of weakening firstly and then strengthening, while its effect on N2O emissions changed from stimulation to inhibition.

“The results suggest that the responses of CH4 and N2O emissions to ECO2 might change with its duration and concentration gradients,” commented Hua Xu.

What does this mean for agricultural practices?

The researchers also elaborated that agricultural management practices such as nitrogen application rates, and straw incorporations, impacted the responses of CH4 and N2O emissions to ECO2. With no or half amount of straw incorporation, ECO2 increased CH4 emissions by up to 49% from paddy fields, respectively.

However, non-significant effects were observed from CH4 emissions under full straw incorporation. With the increasing amount of straw incorporation, the reductions in N2O emissions from paddy fields were enhanced by ECO2.

Compared with continuous flooding, intermittent irrigation weakened the promoted effect on CH4 emissions but stimulated the inhibited effect on N2O emissions from paddy fields under ECO2.

“Therefore, under ECO2 conditions, the increase in CH4 and N2O emissions from paddy fields is decreased with the appropriate agricultural management practices,” explained Guangbin Zhang.

The reduction in CH4 and N2O emissions during the long-term ECO2 (≧10 years) is a new insight into the current scientific community because it has been generally accepted that the ECO2 increases CH4 and N2O emissions from paddy fields.

“These opposite results need further validation. In the future, it is necessary to conduct comprehensive studies at multi-scale, with multi-factor, and by multi-method to effectively reduce the uncertainty in the quantifying the response of CH4 and N2O emissions from paddy fields to the ECO2,” concluded Haiyang Yu.

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