Regional Evaluation of Switchgrass in the Central Valley of California.

In California, switchgrass has not been evaluated and therefore its potential as a source of renewable energy is still unknown. Four field trials were established at four sites in 2007 to evaluate the performance of 11 switchgrass cultivars. The objectives of this study were 1) to calibrate and validate a biogeochemical model (DAYCENT) using published data across the U.S. and data generated from the four field trials in California  and 2) to address the regional sustainability of six cultivars (Alamo, Kanlow, Cave-in-Rock, Dacotah, Sunburst, and Trailblazer) in the Central Valley of California. The model was initially calibrated using published data from sites (5 – 26 sites for each cultivar), where the stand had been maintained for 3 to 10 years with N fertilization (ranging from 0 to 896 kg N ha-1) and 1–4 harvests/year. We assumed that biomass production of switchgrass differed by intraspecific characteristics and it should be constant for the same cultivar anywhere during any growing season if there was no limiting factor. The observed yields varied considerably across the sites and by management practices. The model tends to overestimate the yields in the low range (0–5 Mg ha^-1) but underestimate in the high range (>20 Mg ha^-1) particularly for Alamo, Kanlow, and Cave-in-Rock. This suggests that the model may not simulate the effect of limiting factors realistically due to uncertainty in input parameters at several sites. Nevertheless, there is a general agreement between the simulated and observed yields. The model reproduced the variability of the observed yields reasonably by management and stand age.