An accurate growth model for switchgrass (Panicum virgatum L.) is needed to support decision-making on timing of harvest to predict biomass yield as a function of soil and weather conditions and to maximize resource-use efficiency. The aim was to add a second year of calibration of the ALMANAC model to simulate seasonal changes in biomass yield for Arkansas conditions. Plots were established in 2008 in Fayetteville, AR, with cv. Alamo and were sampled approximately monthly from early May 2009 to mid-February 2010, and again in 2010-2011.  We will report results in the second production year only. Biomass accumulation peaked in late August at 18.8 Mg ha^-1, then decreased by 40% by mid-February. Biomass moisture content declined from 80% to 20% from early May to mid-February. Simulations using ALMANAC will be used to test the predictive ability of the model for biomass yield using a calibration from the 2009 growing season. This will indicate whether further calibration is needed to improve accuracy across years.