Correlating bulk density (with dockage) and test weight (without dockage) for wheat samples

Authors: BHADRA, RUMELA - KANSAS STATE UNIVERSITY; CASADA, MARK; BOAC, JOSEPHINE - KANSAS STATE UNIVERSITY; TURNER, AARON - UNIVERSITY OF KENTUCKY; THOMPSON, SIDNEY - UNIVERSITY OF GEORGIA; MONTROSS, MICHAEL - UNIVERSITY OF KENTUCKY; MAGHIRANG, RONALDO - KANSAS STATE UNIVERSITY; MCNEILL, SAMUEL - UNIVERSITY OF KENTUCKY

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2016
Publication Date: 11/1/2016
Citation: Bhadra, R., Casada, M.E., Boac, J.M., Turner, A.P., Thompson, S.A., Montross, M.D., Maghirang, R.G., McNeill, S.G. 2016. Correlating bulk density (with dockage) and test weight (without dockage) for wheat samples. Applied Engineering in Agriculture. 32(6):926-930. https://doi.org/10.13031/aea.32.11692.
DOI: https://doi.org/10.13031/aea.32.11692

Interpretive Summary: Grain stored in bins compacts due to overburden pressure created by the cumulative weight of the grain above, which increases the stored grain bulk density and, thus, storage capacity. The increase in storage capacity requires accurate pack factor values to use with measured initial bulk density for determining grain inventory. The U.S. grain industry uses standard grading guidelines from the USDA Federal Grain Inspection Service (FGIS) handbook that states test weight—the initial bulk density of grain when measured following FGIS guidelines—for hard red winter wheat should be measured and reported without dockage, where dockage is mostly non-wheat material that can be readily removed from the wheat using appropriate cleaning equipment. However, to determine the amount of compaction of stored grain in a bin it is essential to have the initial bulk density with dockage included. This study addresses this problem by developing predictive models to calculate the bulk density with dockage when test weight without dockage is known. Predictive models were validated for varying dockage levels along with an overall model that can handle any dockage level from 0% (i.e. no dockage) to 3% at normal stored wheat moisture contents (10% to 13% wb). The models were effective for normal dockage levels, less than 1%, as well as for higher levels seen in a poor harvest year. These models will be highly beneficial to elevator managers and others working with wheat compaction and inventory, making accurate inventory calculations possible without the excessive difficulty of re-sampling and measuring bulk density with dockage for the entire bin.

Technical Abstract: In grain bins the compaction of stored grain is caused by the overbearing pressure of the bulk material in the bin. To predict the amount of grain in the bin, compaction must be determined based on the average initial bulk density of the stored material. However, initial bulk density is determined following the Federal Grain Inspection Service (FGIS) guidelines for measuring test weight (TW), which require that dockage be removed prior to measuring wheat TW. This creates a problem for predicting grain compaction and conducting inventory studies, because the initial bulk density of the grain in a bin for these calculations should include dockage. Therefore, regression models between the TW without dockage and the bulk density with dockage were obtained based on the reported scale data during wheat harvest from three elevators located in Kansas and Oklahoma. A power model was used to predict bulk density with dockage when test weight without dockage and dockage levels are given. Laboratory samples of HRW and SRW wheat with dockage levels ranging from 0.05% to 5% showed a second order polynomial trend when plotted against decrease in bulk density with dockage values compared to test weight without dockage. These results will be crucial for determining grain packing inventory parameters for HRW wheat bins.