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Using a crop/soil simulation model and GIS techniques to assess methane emissions from rice fields in Asia. I. Model development

: Matthews, R.B.; Wassmann, R.; Arah, J.


Nutrient cycling in agroecosystems 58 (2000), Nr.1/3, S.141-159
ISSN: 1385-1314
Fraunhofer IFU; 2002 in Helmholtz-Gesellschaft integriert
methane; rice; Oryza sativa; anaerobic; model; simulation; carbon dynamics

The development of the MERES (Methane Emissions in Rice EcoSystems) model for simulating methane (CH sub 4) emissions from rice fields is described. The CERES-Rice crop simulation model was used as a basis, employing the existing routines simulating soil organic matter (SOM) decomposition to predict the amount of substrate available for methanogenesis. This was linked to an existing submodel, described elsewhere in this volume (Arah & Kirk, 2000), which calculates steady-state fluxes and concentrations of CH sub 4 and O sub 2 in flooded soils. Extra routines were also incorporated to simulate the influence of the combined pool of alternative electron acceptors in the soil (i. e., NO sub 3 high -, Mn high 4+, Fe high 3+, SO sub 4 high 2-) on CH4 production. The rate of substrate supply is calculated in the SOM routines of the CERES-Rice model from (a) the rate of decomposition of soil organic material including that left from the previous crop and any additions of organic matter, (b) root exudates (modified from the original CERES-Rice model using recent laboratory data), and (c) the decomposition of dead roots from the current crop. A fraction of this rate of substrate supply, determined by the concentration of the oxidized form of the alternative electron acceptor pool, is converted to CO sub 2 by bacteria which outcompete the methanogenic bacteria, thereby suppressing CH sub 4 production. Any remaining fraction of the substrate supply rate is assumed to be potentially available for methanogenesis. The CH sub 4 dynamics submodel uses this potential methanogenesis rate, along with a description of the root length distribution in the soil profile supplied by the crop model, to calculate the steady-state concentrations and fluxes of O sub 2 and CH sub 4. The reduced form of the alternative electron acceptor pool is allowed to reoxidize when soil pores fill with air if the field is drained. The MERES model was able to explain well the seasonal patterns of CH sub 4 emissions in an experiment involving mid- and end-season drainage and additions of organic material at IRRI in the Philippines.