Calibrating ALMANAC for Simulating Switchgrass Production in Arkansas.

An accurate growth model for switchgrass (Panicum virgatum L.) is needed to support decision-making on timing of harvest by predicting biomass yield as a function of soil and weather conditions and to maximize resource-use efficiency. The aims were to characterize seasonal trends in biomass yield and to calibrate and verify the ALMANAC model to improve crop growth simulation for Arkansas conditions. Plots were established in 2008 in Fayetteville, AR, with cv. Alamo and were sampled approximately monthly from 1 May 2009 to 17 February 2010. Biomass accumulation peaked at in late August at 13.2 Mg/ha, then decreased by almost 26% by mid-February. ALMANAC calibration included adjustments of potential heat unit and subsurface flow values. These adjustments resulted in simulated values falling within 1 SD unit of observed yields from May-November. Simulated yields overestimated observed yields by more than 1 SD unit in December-February because the model apparently did not predict wheathering losses of the standing crop. The calibrated model was verified by accurately predicting October-harvested biomass yields observed at two Arkansas locations over two years. ALMANAC can effectively predict switchgrass biomass yields, pending further verifications using additional location-years.