Optimal Time to Replace Switchgrass Stand with a More Productive Variety

The net present value (NPV) criterion was employed to develop an economic model that can be used to determine if and when it is optimal to replace an existing switchgrass stand with an alternative higher biomass yielding cultivar. Yield data from a randomized field experiment conducted from 1994 to 2000 in Haskell and Chickasha, Oklahoma were used to represent average yields for the defender. The study assumed a constant and a declining future yield scenario for the defender. Under the assumptions used in the study, it was optimal to renovate a switchgrass stand if the improved cultivar produced a higher biomass yield of 16% or more for a 20 year planning horizon. The estimated breakeven NPV of the defender and challenger was $229 ha-1. For a plot with declining yields, the defender would have to be retained for about six years before being optimally replaced by a 10% yield increment challenger whereas a higher biomass yielding challenger would replace the defender immediately.