Abstract

In rice paddy, the closed chamber method is broadly used to estimate methane (CH4) emission rate. Since rice plants can significantly affect CH4 production, oxidation and emission, rice plantation inside the chamber is standardized in IPCC guidelines. Methane emission rate is calculated using the increased concentration inside the headspace. Biomass growth might decrease the headspace volume, and thus CH4 emission rates might be overestimated. To evaluate the influence of chamber headspace decreased by rice plant development on CH4 emission rates, five Korean rice cultivars were cultivated in a typical rice paddy, and physical volume changes in rice biomass were assayed using water displacement method. The recommended acrylic closed chambers (H. 1.2 m x W. 0.6 m x L. 0.6 m) were installed, and eight rice plants were transplanted inside the chamber with the same space interval with the outside. Biomass growth significantly decreased the headspace volume of the chamber. However, this volume covered only 0.48–0.55% of the closed chamber volume at the maximum growth stage. During the whole cropping period, mean 0.24–0.28% of chamber headspace was allocated by plant biomass, and thus this level of total CH4 emissions was overestimated. However, this overestimation was much smaller than the errors coming from other investigation processes (i.e., chamber closing hour, temperature recording, inconstant flooding level, different soil environments, etc.) and rice physiological changes. In conclusion, the influence of physical biomass volume inside the closed chamber was negligible to make the error in total CH4 emission assessment in rice paddies.

Highlights

  • Methane (CH4) is the second potent greenhouse gas (GHG) after carbon dioxide (CO2) and contributed to approximately 18% of total global warming over the last 50 years [1]

  • Soil Eh values were not discriminated among rice cultivars

  • To calculate CH4 emission rates in closed chamber method (Eq 1) [21], the increased CH4 concentration and temperature for chamber closing hour were considered as the variables

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Summary

Methods

The experimental plots were installed at the agronomic rice field of Gyeongsang National University (35 ̊0805600N and 128 ̊0504600E), Jinju, South Korea. The region has a typical temperate monsoon climate. For the last 30 years, the mean temperature and annual precipitation were 13 ̊C and 1513 mm, respectively [30]. The soil was classified as Pyeongtaeg series (fine-silty, mixed, nonacid, mesic Typic haplaquent) and the field was exclusively utilized for rice. The difference of CH4 fluxes between rice included chamber and bare soil chamber cultivation for over 40 years. Soil had slightly acidic pH (5.9±0.2, 1:5 with H2O) and low fertility (21.5±2.3 g kg-1 of organic matter, 0.71±0.06 g kg-1 of total N, and 41±4.1 mg kg-1 of available P).

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