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United States Department of Agriculture

Agricultural Research Service

Research Project: Establishing New Grain Packing Factors: Field Data from the Western U.S.

Location: Engineering and Wind Erosion Research Unit

2012 Annual Report


1a.Objectives (from AD-416):
Obtain new field data to refine and calibrate a science-based model for determining the packing of grains within upright storage structures. The Cooperator will obtain field measurements of grain packing from the major grain producing regions of the U.S. with collaborators at ARS, the University of Kentucky, and the University of Georgia who will also make field measurements. Field data will be collected for wheat, corn, soybeans, grain sorghum, oats, and barley. The effect of aeration systems on packing factor will also be investigated.


1b.Approach (from AD-416):
This research is part of a larger, nationwide project to refine and validate a procedure with known accuracy, based on measurable physical parameters, for determining the packing of grains within upright storage structures. Because grain is somewhat compressible when subjected to the cumulative weight exerted from the material above, accurate packing factors are required to determine the mass of grain in storage from bin dimensions and test weights. Inventory control is critical for stored grain managers due to financial aspects (auditing by state agencies) and for the future utilization of quality management systems. The major variables affecting stored grain packing are grain type, moisture content, test weight, internal friction, and bin wall material, geometry, and dimensions. Variation across different regions of the U.S. must be investigated as well as other minor factors. A preliminary model for determining packing factors for a wide range of grains and bins is being developed at the University of Georgia that employs the differential form of Janssen’s equation to estimate the pressure and in-bin bulk density for a given depth of grain in a bin. In the larger project, this model will be calibrated and validated by measuring packing factors for selected grains in bins in all of the major grain producing regions of the U.S. As part of that nationwide effort, the Cooperator will measure packing factors in selected states west of the Mississippi River. Field measurements of packing factors will be obtained by measuring the height of grain in bins of known dimensions and wall materials as they are filled and/or discharged with a measured mass of grain.


3.Progress Report:

In order to develop improved predictions of stored grain packing factors, existing compaction levels are being measured in the field for numerous common bin sizes and types on farms and at grain elevators around the U.S. We have measured more than 50 hard red winter (HRW) wheat bins (including both concrete and corrugated steel) across the Central U.S. for determining packing factor. Packing factor measurements were taken for 30 corn bins from the Central and Midwest U.S. and the eastern part of Mississippi River Valley. In addition, 12 oat bins, 8 soybean bins, and 3 grain sorghum bins were measured to determine packing factor. The overall evaluation of the wheat field data showed that our current packing model was slightly under-predicting packing factor and, thus, grain weight. The percentage difference between reported (actual) grain weights and model predicted was always below 8%. However, non-circular wheat bins showed a greater tendency to over-predict. For corn bins, field data showed that the current packing model (based on preliminary tests) was mostly under-predicting. The percentage difference between reported (actual) grain weights and model predicted was always below 4%. More field data for corn is being collected this fall to confirm this difference. For the limited soybean bins, field data showed that the current packing model was mostly under-predicting and the percentage difference between reported (actual) grain weights and model predicted weights (based on preliminary tests) were consistent at 5%. Oat bins have not yet been evaluated because the prediction models for oats are incomplete. This extensive field data is contributing to a greater understanding stored grain packing factors and should provide greater confidence in the packing factor predictions being developed compared to the old packing factor predictions.


Last Modified: 7/25/2014
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