Straw Application Altered CH 4 Emission, Concentration and 13C-Isotopic Signature of Dissolved CH 4 in a Rice Field

Abstract

CH 4 emission and the concentration of dissolved CH 4 in soil solution and floodwater in a rice field and their stable carbon isotopic signatures as affected by straw application were investigated in 2009 in a field experiment at Jurong, Jiangsu Province, China. Straw application increased CH 4 emission and CH 4 concentration in the soil solution and floodwater. A positive seasonal correlation was also observed in the variation between CH 4 flux and CH 4 concentration in soil solution. The seasonal total CH 4 emission (51.6 g CH 4 m −2) in Treatment WS (straw applied) was about 168% higher than that in Treatment CK (without straw). The emitted CH 4 and CH 4 in soil solution were initially relatively enriched, then depleted and finally enriched again in 13C in both treatments, while CH 4 in floodwater became isotopically heavier. The carbon isotopic signature of emitted CH 4 and CH 4 in floodwater averaged around −62‰ and −45‰ for both treatments, respectively, and was not significantly influenced by the application of straw. However, straw application caused the CH 4 in soil solution to be significantly depleted in 13C during the middle of the rice season, and the mean δ 13C value was lower in WS (−57.5‰) than in CK (−49.9‰). Calculation from the isotopic data showed that straw application increased the fraction of CH 4 oxidized, causing no significant difference in the δ 13C value of the emitted CH 4 between the two treatments.