Study shows increased energy balance
The reason for the increase is that yields and technologies are becoming better, explained Assistant Professor Dev Shrestha, who collaborated on the project with Jon Van Gerpen, department head of biological and agricultural engineering, and graduate student Anup Pradhan. The study was based on biodiesel production from soybean oil, similar to the 1998 study. According to the National Biodiesel Board, the new analysis is more comprehensive than previous work; it even includes the energy required to manufacture the farm machinery used to produce soybeans.
For more than three years, the researchers collected data from the USDA agricultural survey reports published by the USDA Economic Research Service, as well as from some industry surveys and literature, Shrestha explained. The data was incorporated into the biodiesel plant process model developed by the USDA Agricultural Research Service and trademarked as SuperPro Designer Model.
They found national soybean yields had increased at the rate of 0.6 bushels per acre per year, based on yield data from 1975 to 2006. Meanwhile, since 2000, the fertilizer application rate has essentially remained the same, and the herbicide application rate has declined to one-fifth of its previous rate. Reduced herbicide applications mean that less diesel is required for field spraying.
Shrestha told Biodiesel Magazine he plans to update the carbon balance of biodiesel next.