According to reports, a company service technician discovered the blade on the ground on Friday.
Siemens has launched an investigation of the incident. "We don't know yet why this happened, but we are committed to conducting a detailed engineering analysis to determine the root cause," Siemens said in a statement.
There were no reports of injuries. The blades for the Eclipse project were manufactured at the company's facility in Fort Madison, Iowa. MidAmerican announced completion of the project on 31 December 2012, as the previous production tax credit expired.
Siemens was handed the contract from MidAmerican for Eclipse in February last year. The deal was part of a 407MW supply contract that includes two other projects.
Incidents involving the Siemens 2.3 turbine are relatively few. However, in 2010 a blade broke off a 2.3MW turbine at the 322MW Whitelee wind farm in Scotland, UK.
Following that incident, Siemens said an examination of the broken blade revealed a "material defect in the laminate". The company said these could be the result of changes to the manufacturing process.