Effect of urea on CH_4 flux under the oil palm (Elaeis guineensis) on tropical peatland in Sarawak, Malaysia

摘要

Methane flux was measured monthly from August 2002 to July 2003 at an oil palm plantation on tropical peatland in Sarawak, Malaysia using a closed chamber technique. Urea was applied twice in November 2002 and May 2003. The monthly CH_4 flux ranged from -32.78 to 4.17 μg C m~(-2) h~(-1). Urea applications increased CH_4 emissions in the same month of application and slightly a month later before the effect disappeared in the 3rd month after application i.e. back to CH_4 uptake. This short-term effect was due to the increased soil NH_4~+ content that was not immediately absorbed by the oil palm following urea application, which reduced the oxidation of CH_4 resulting in its enhanced emission. By using the Cate-Nelson linear-plateau model, the critical soil NH_4~+ content causing CH_4 emissions in the oil palm ecosystem was 42.75 mg kg~(-1) soil. However, the inhibitory effect of NH_4~+ on the oxidation of CH_4 was mitigated by low rainfall and pyrophosphate solubility index (PSI) which may probably be due to increased oxidation of the CH_4 and low soluble substrate for methane production. Thus, splitting and timing of urea applications are important not only to optimize oil palm yield but also reduce soil NH_4~+ content in order to minimize CH_4 emissions and therefore, its potential negative impact on the environment.