Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2006
Publication Date: 3/1/2007
Citation: Raper, R.L., Arriaga, F.J. 2007. Comparing Peak and Residual Soil Pressures Measured by Pressure Bulbs and Stress-State Tranducers. Transactions of the ASABE. 50(2):339-344. Interpretive Summary: Extremely heavy agricultural vehicles excessively compact soil and hinder crop growth. However, the ability to determine when a vehicle is too heavy is difficult due to transducers which are difficult to use and require significant instrumentation. An experiment was conducted that compared the ability of a simple rubber pressure bulb to measure differences in soil compaction with a more complicated electronic transducer. The transducers performed similarly, but the rubber pressure bulb had greater sensitivity and could distinguish between the loads applied to greater depths than the electronic transducer. Continued testing and development of the rubber pressure bulbs could lead to improvements in soil compaction management by allowing producers to know when their vehicle loads are excessive and could cause significant soil damage.
Technical Abstract: Measurement of soil pressures caused by vehicle loading is difficult and often subject to extreme variability. Two types of soil transducers were compared in an experiment conducted in a Norfolk sandy loam soil in the USDA-ARS National Soil Dynamics Laboratory’s (NSDL) soil bin facilities. Stress state transducers (SST), electronic transducers developed at the NSDL for measuring six directional pressures and determining the stress state, were used for this experiment. Rubber bulbs connected by a rubber hose to a dial pressure guage, which measure hydrostatic pressure, were also used in this experiment. Both transducers were buried at depths of 7.5, 15, or 23 cm and were used to measure soil pressures caused by a 30.5L-32 tire with dynamic loads of 19 or 37 kN. The SST’s were buried by inserting them into an excavated hole while the rubber bulbs were inserted by a special tool designed to leave the soil surface and surrounding soil undisturbed. Peak values of mean normal stress (calculated from measurements of pressure) from the SST and hydrostatic pressure measured with the rubber bulbs were found to be affected by both loading and burial depth. Similar magnitudes and variation were observed for each transducer. Residual pressure, defined as the pressure remaining after loading was removed, was found to be affected by both loading and burial depth when measured with the rubber bulbs. Continued development and testing of the rubber bulb transducers could provide a simple method of determining levels of compaction that could damage soils and thus prevent excessive trafficking.