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Triggering of Methane Production in Rice Soils by Root Exudates

Effects of Soil Properties and Crop Management

^a The Energy and Resources Institute, Darbari Seth Block, Habitat Place, Lodhi Road, New Delhi, 110003, India
^b Center for Development Research (ZEFc), Univ. of Bonn, Walter-Flex-Str. 3, D-53113, Bonn, Germany
^c Institute for Meteorology and Climate Research-Atmospheric Environmental Research—Forschungszentrum Karlsruhe, Kreuzeckbahnstr. 19, D-82467, Garmisch-Partenkirchen, Germany
^d USDA-ARS, National Soil Tilth Lab., 2150 Pammel Drive, Ames, IA 50011

View larger version (25K): [in a new window]   Fig. 1. Daily rates of CH4 production for lowland rice soils taken from five farmers' fields for (a) the unamended control treatment during a 70-d pre-incubation plus an additional 20 d that corresponded to the post-spiking incubation, and during a 20-d incubation following spiking at 70 d with (b) glucose and (c) rice root exudates. From 0 to 70 d, trends in the control treatment were identical to those of the glucose and root exudate treatments (not shown). Vertical bars represent standard errors of three laboratory replicates. Units of the samplings from 0 to 24 h after spiking (inset graphs) are µg CH4 g –1 soil d–1.

View larger version (33K): [in a new window]   Fig. 2. Total CH4 production for five rice soils taken from farmers' fields (a) during a 70-d pre-incubation, and (b) during a 20-d incubation following spiking with glucose or root exudates compared with the unamended control treatment. Vertical bars represent standard errors of three laboratory replicates.

View larger version (33K): [in a new window]   Fig. 3. Daily rates of CH4 production for lowland rice soils taken from four crop management treatments on the IRRI research farm. IRRI-1 is double-cropped rice with removal of aboveground crop residues and anaerobic decomposition of crop roots. IRRI-2 is double-cropped rice with anaerobic decomposition of all crop residues. IRRI-3 is double-cropped rice with aerobic decomposition of all crop residues. IRRI-4 is a rice-maize rotation with aerobic decomposition of all crop residues. The graph for the unamended control treatment shows production rates during a 70-d pre-incubation plus an additional 20 d that corresponded to the post-spiking incubation. Graphs for each of the four management treatments depict CH4 production during the 20-d incubation following spiking with glucose or root exudates compared to the unamended control. Units of the samplings from 0 to 24 h after spiking (inset graphs) are µg CH4 g –1 soil d–1. Vertical bars represent standard errors of three laboratory replicates. Abbreviations: DOI, days of incubation; DAS, days after spiking.

View larger version (32K): [in a new window]   Fig. 4. Total CH4 production for rice soils taken from four crop management treatments on the IRRI farm (a) during a 70-d pre-incubation, and (b) during a 20-d incubation following spiking with glucose or root exudates compared with the unamended control treatment. Management treatments are explained in Fig. 3. Vertical bars represent standard errors of three laboratory replicates.