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Dissolved Organic Carbon and Methane Emissions from a Rice Paddy Fertilized with Ammonium and Nitrate

China National Rice Research Institute, Hangzhou, Zhejiang 310006, P.R. China;

Reiner Wassmann

Fraunhofer Institute for Atmospheric Environmental Research, Garmisch-Partenkirchen, Germany;

Heinz-Ulrich Neue

UFZ-Center for Environmental Research, Department of Soil Sciences, Theodor-Lieser Strasse 4, D-06120 Halle, Germany;

Changyong Huang

College of Resources and Environmental Sciences, Zhejiang University, China.

^* Corresponding author (lyahai{at}nuagr1.agr.nagoya-u.ac.jp).

ABSTRACT

The effect of nitrogen fertilizers on methane (CH₄) production and emission in wetland rice (Oryza sativa L.) is not clearly understood. Greenhouse pot and laboratory incubation were conducted to determine whether the effect of N type (NH₄-N and NO₃-N) and rate (30 and 120 kg N ha^–1) was related to the availability of carbon for CH₄ production in flooded rice soils. In addition to CH₄ emission rates, seasonal patterns of dissolved organic carbon (DOC) and dissolved CH₄ were determined in soil solutions of the root zone (soil surrounding rice roots) and the non-root zone (soil outside the root zone). Dissolved organic C in the root zone increased with plant growth and reached a maximum (16 to 21 mmol C L^–1) at 1 wk after flowering, whereas DOC in the non-root zone remained relatively low (1 to 5 mmol C L^–1). The increase of dissolved CH₄ concentrations was quicker and greater in the root zone (111 to 170 mol L^–1) as compared with the non-root zone (54 to 117 mol L^–1). Methane emission increased from 0 to 1.0 mmol CH₄ plant^–1 d^–1. From panicle initiation (PI) to maturation, the root zone DOC concentration was lower with NO₃-N application (8 to 13 mmol C L^–1) than with NH₄-N (13 to 21 mmol CL^–1). Similarly, NO₃-N application reduced dissolved CH₄ concentration as well as CH₄ emission. Anaerobic incubation showed that the inhibitory effect of NO₃-N addition on CH₄ production lasted only 2 wk. Thus, the inhibitory effect of NO₃-N seemed not fully accountable for the prolonged reduction in CH₄ production and emission in the fields. The root zone DOC that is enriched by plant-borne C appears to be a main source for CH₄ production and the lower DOC concentrations with NO₃-N application are accountable for the low CH₄ emissions.

Present address: Lab. of Soil Biology and Chemistry, Graduate School of Bioagricultural Sciences, Nagoya University, Chikusa, Nagoya, 464-8601 Japan.

Present address: Soil and Water Sciences Division, International Rice Research Institute (IRRI), P.O. Box 3127, 1271 Makati City, Philippines.

This research was conducted in the Soil and Water Sciences Division, International Rice Research Inst., Los Banos, Laguna, the Philippines.

Received for publication December 3, 1999.