Modeling Biomass Production

Simulating Plant Growth

Agro-BGC, ALMANAC, BIOCRO, DAYCENT, EPIC, and SWAT are six mechanistic models that have been used to simulate switchgrass productivity (Williams et al. 1989; Kiniry et al. 1992; Kiniry et al. 1996; Arnold et al. 1998; Del Grosso et al. 2005; Di Vittorio et al. 2010; Miguez et al. 2011). Each model keeps track of the number of growing degree-days to specify the developmental rate or phenological stage of switchgrass. The number of growing degree-days is determined by the average of the daily maximum and minimum temperature above the specified baseline temperature (Williams et al. 1984). ALMANAC, EPIC, and SWAT use a function relating radiation use efficiency to biomass based on the leaf area and the amount of light intercepted (Williams et al. 1989). For switchgrass, plant development is initiated when temperatures exceed 12°C (ALMANAC, EPIC, and SWAT). Senescence begins when plants exceed the maximum number of growing degree days (Williams et al. 1989; Kiniry et al. 1992).

Biomass is partitioned into roots and shoots. The DAYCENT model uses a constant energy biomass conversion factor (Parton et al. 1998). BIOCRO was developed from WIMOAC and uses an empirical derivation of the relationship between photosynthesis, stomatal conductance, and biomass production (Humphries and Long 1995; Miguez et al. 2011). Agro-BGC relies on a mechanistic formulation of carbon uptake and assimilation (Di Vittorio et al. 2010).