Study Methodology
The study’s first step was to estimate the total quantity of biomass available from agricultural sources because that sector was expected to be a leading provider. The approach was to estimate the total quantity produced, recognizing that not all biomass produced annually would be harvested. Agronomists and environmentalists advocate harvesting only a portion of total biomass available to maintain soil fertility, minimize erosion, and provide wildlife habitat. Thus, only a portion of the biomass inventory shown in the database is available for commercial use.
Annual crop production for each North Dakota county was obtained using county level data reported by the National Agricultural Statistics Service (NASS). The annual estimates were obtained by averaging production for years 2007 and 2008. Conversion factors for weights and the standard bulk density by crop were utilized to calculate metric dry tons produced. Finally, the biomass conversion equations were applied to each total to calculate the amount of residue from each crop. These conversion equations by crop type are summarized in Table-1 below.
Table-1| Crop Type | Biomass Conversion Equations (in tons) |
| Wheat Barley Oats3 |
Production*residue factor*available factor*(1- moisture content) Residue factor = 2.5 Available factor = 0.25 Moisture content = 8% |
| Corn3 | Production*residue factor*available factor*(1- moisture content) Residue factor = 1.1 Available factor = 0.25 Moisture content = 47% |
| Hay | Obtained directly from NASS |
| Potato3 | Production*processing percentage*solid waste *(1- moisture content) Processing percentage = 56.7% Solid waste of the raw potato being processed= 3.7% Moisture content = 81% |
| Soybeans Dry Beans Peas Lentils2 |
Production*crop to residue ratio*(1- moisture content) Crop to residue ratio = 1.2 Moisture content = 13% |
| Sunflowers Canola1 |
Production*crop to residue ratio*(1- moisture content) Crop to residue ratio = 3.7 Moisture content = 30% |
| Sugarbeats Flaxseed1 |
Production*crop to residue ratio*(1- moisture content) Crop to residue ratio = 0.4 Moisture content = 60% |
Sources:
1 1st World Conference on Biomass for Energy and Industry
2 Milbrandt
3 Frear et al.
NASS crop production information is developed from farm survey information. While county data for all crop classes combined are available, they create an obstacle when it comes to reconciling total county production to district and state production. For this reason, it is recommended to access individual county data for each crop class rather than data for all crop classes combined. NASS data excludes certain counties or districts when too few observations are available for individual crop classes. Thus only combined (e.g. other spring, durum, and winter wheat) estimates are available. Several counties and two districts are combined into “Combined Counties” and “Combined Districts” and their reported production vary from year to year. For example, in 2007 the amount of unallocated wheat county production was less than 0.1% (188,000BU) of the total production, while in 2008 the same mount was 2.1% (6.4 million BU). In order to reconcile total county production to the state production, the amount of production reported for “Combined Counties” is allocated back to counties based on the county-to-district contribution. The “Combined Districts” production is allocated back to county based on county-to-state contribution. For a few crops such as canola (District 60), beans (Districts 70 and 80), and potato (District 10, 80), the “Combined District” production is reported only. Since there is no any information which county contributes to the overall district production, the “Combined District” production is evenly distributed among all counties within the district.
The municipal wood –based biomass estimates for six major North Dakota Cities were obtained by contacting city managers at landfill sites. These cities include: Fargo, Bismarck, Grand Forks, Williston, Mandan, and Dickinson. City managers were asked to quantify the wood and yard waste collected by type for the most recent two year. Most cities shared their annual reports showing all categories of waste by type and quantity. A few cities such as Jamestown and Minot reported some inadequate data which had to be disregarded in this analysis. For instance, city managers in Minot estimated the quantity of wood waste based on the experience and financial cost involved in mulching and grinding yard waste. Jamestown does not have yard service available where the yard waste can be collected at the curb. Instead, they take all yard waste to a designated field in town for a disposal. City manager in Jamestown estimated the amount of waste collected at this designated field; however, it could not be separated by type. Additional details from these surveys are provided in the Appendix.
For other cities in North Dakota, it was assumed that municipal yard waste is directly related to the population count. The US Census 2007 Population estimates were obtained for all cities and counties in North Dakota. Population estimates were linked to those cities from which data on municipal yard waste was obtained in order to develop a simple linear regression model.
Y = α + βX + ε
X – population
Y – municipal yard waste
ε – error term
A statistical analysis was completed using SAS software to develop the best fitting line and determine how well the model fit the data and should it be used for predicting the year waste quantity based on the population statistics. The R-square was 86.68% indicating that the model was a good fit as such the model was used to estimate the quantity of yard waste collected for the remaining area in North Dakota based on the population data.
Logging residue estimates and dry biomass of timberland trees were queried off the USDA Forest Service Timber Product Output (TPO) Database vintage 2007. The volume of logging residue was reported in cubic feet. In order to be consistent with units of biomass presented by other resources , the conversion factor used was 30 dry pounds per cubic foot or 15 dry tons of residues per thousand cubic feet of residue reported (Perlack at al. 2005).
Finally a small amount of hay and wood based residues lay in National and State Parks across the state. A report prepared by North Dakota Forest Service was used to obtain this information.