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Modifying DSSAT Crop Models for Low-Input Agricultural Systems Using a Soil Organic Matter–Residue Module from CENTURY

^a Centro Internacional de Agricultura Tropical (CIAT), Apartado Aéreo 6713, Cali, Colombia
^b Dep. of Biol. and Agric. Eng., Univ. of Georgia, Griffin, GA 30223
^c Nat. Resour. Ecology Lab., Colorado State Univ., Fort Collins, CO 80523

View larger version (26K): [in a new window]   Fig. 1. The pool and flow structure of the (a) CERES-based and (b) CENTURY-based soil organic matter (SOM)–residue modules of DSSAT. Each of the decomposition flows (vertical arrows) between pools (boxes) is accompanied by either N mineralization or immobilization.

View larger version (26K): [in a new window]   Fig. 2. (a) Soil temperature and (b and c) soil water factors in the (b) CERES-based and (c) CENTURY-based soil organic matter (SOM)–residue modules. For both modules, the curves of the soil water factor will be different for each soil as they vary with the soil water parameters field capacity and wilting point (CERES-based module) and soil texture plus bulk density (CENTURY-based module). The curves presented here are just examples. For the CENTURY-based module, "coarse," "medium," and "fine" have been given bulk densities of 1.6, 1.5, and 1.3 g cm-3, respectively.

View larger version (23K): [in a new window]   Fig. 3. (a) Decomposition pattern of Cajanus cajan residues as simulated with the CERES-based (dashed line) and CENTURY-based (solid line) soil organic matter (SOM)–residue modules. (b) Nitrogen mineralized from C. cajan residues as simulated with the CERES-based (dashed line) and CENTURY-based (solid line) SOM–residue modules, and N immobilized by microbes with the original parameter settings (dotted line) and with the modified parameter settings (dashed-dotted line), as simulated by the CENTURY-based SOM–residue module. Residues with a N concentration of 2.35% were applied at 10495 kg ha-1; they were incorporated at a 20-cm depth.

View larger version (16K): [in a new window]   Fig. 4. Mineral N concentration of the (a) 0- to 15- and (b) 15- to 30-cm soil layers under fallow with Cajanus cajan residues, as measured () and as simulated with the CENTURY-based soil organic matter (SOM)–residue module with the soil texture of all layers set to 100% sand (solid line) or 100% clay (dotted line). The residues applied were 10495 kg ha-1 of C. cajan tops with a N concentration of 2.35%.

View larger version (18K): [in a new window]   Fig. 5. Soil organic C content of the 0- to 23-cm layer of the soil under bare fallow in the Rothamsted Highfield bare fallow experiment, as simulated with the CERES-based (dashed line) and CENTURY-based (solid line) soil organic matter (SOM)–residue modules.

View larger version (44K): [in a new window]   Fig. 6. Mineral N concentration of the (A) 0- to 15- and (B) 15- to 30-cm soil layers under fallow, without or with various residues, as measured () and as simulated with the CERES-based (dotted line) and CENTURY-based (solid line) soil organic matter (SOM)–residue modules. The treatments applied were (a and b) bare fallow, (c and d) Cajanus cajan (10495 kg ha-1 with a N conc. of 2.35%), (e and f) Calopogonium mucunoides (7586 kg ha-1 with a N conc. of 2.17%), (g and h) Canavalia brasiliensis (8214 kg ha-1 with a N conc. of 2.41%), (i and j) C. ensiformis (9514 kg ha-1 with a N conc. of 2.68%), (k and l) Crotalaria striata (12444 kg ha-1 with a N conc. of 2.16%), (m and n) Pueraria phaseoloides (4758 kg ha-1 with a N conc. of 1.91%), and (o and p) Mucuna aterrima (5907 kg ha-1 with a N conc. of 2.37%).