Harvesting Bioenergy

One objective of the Wildlife & Bioenergy project is to measure the bioenergy potential of grassland biomass harvested in the Upper Midwest. Each summer subsamples of vegetation are collected to estimate the productivity of the plot. This value is compared to the biomass yields measured during the production-scale harvest to estimate harvest efficiency. Biomass yields are calculated by multiplying the number of bales produced by the average bale weight, then dividing that by the area cut. 

The treatment imposed is harvest intensive with each plot harvested in the autumn leaving a certain size and shape refuge of standing vegetation for wildlife. 

Harvesting grasslands in autumn, after the plants have senesced and migratory birds have left for the winter, appears to be the optimal time to maximize bioenergy potential of biomass. This raises logistic challenges for farmers who also manage croplands that require autumn harvest, since the window of opportunity is small due to early winter snowfall. This project provides valuable information on the time and resource requirements for conducting a grassland biomass harvest. Our team has contracted a company that utilizes the most advanced equipment designed specifically for harvested mixed forage biomass. Given that we are harvesting many small plots scattered across the western edge of Minnesota and leaving very specific refuge sizes in most plots, it has been difficult to harvest the 720 acres scheduled each season. 

After the harvest is complete, cores from a sample of bales were collected from each plot and analyzed for elements related to plant growth rates (i.e. N, P, K, S, Ca, Mg, Na, Zn, Fe, Mn, Cu, and B). Bale cores are also analyzed for energy content, forage quality and moisture content. The image on the right shows how bale cores are collected for analysis. These data sets are used to determine the quality of the biomass for energy production, and can be used as parameters in economic models.  Outlines of harvested areas were mapped with GPS units and converted to a GIS layer for mapping and precise calculations of harvest areas. Stubble height was measured at randomized locations throughout the cut areas in each plot.


Ecosystem Services 

Harvesting restored prairies may affect the ecosystem processes within the prairie, setting an off balance of the ecosystem. To explore the relationship between biomass harvest and carbon sequestration, soil cores were collected at the start of the project and will also be collected during the final year of the research to measure the influence of biomass harvest on soil composition.