Forest Research Soil Penetrometer
A soil penetrometer is used to measure the degree of soil compaction, or bulk density of a soil (grams per cubic centimetre), by the soils resistance to the penetration of the penetrometer cone. Penetrometers can be used to indicate how dense soil layers are, in comparison to other soil types or differing soil horizons, within a soil type. These measurements can be useful when assessing a soils bearing capacity for civil engineering construction e.g. roads and building foundations.
However, when planting trees it can be a very important measure of the potential of a soil/site to allow the trees to produce an unconstrained roots system, able to fully exploit the available soil nutrients, water and yet resist windthrow by anchoring the tree roots. If the bulk density of a soil exceeds 1.7 - 2.0 grams per cubic centimetre, within 60cm of the surface, this can restrict the trees ability to exploit the site and make the tree more susceptible to windthrow.
These were the reasons for Forest Research to ask their Alice Holt workshop to produce a robust yet portable penetrometer that could be used to gather comparative penetration data in the field. I can vouch that this instrument was both robust and "portable", just!
The striker/weight is raised to the upper stop and then dropped a set distance to impact the anvil at the base of the rod and drive the selected cone into the soil. Opposite to the weight handle there is a pencil mounted, so that it can be used to scribe a mark on the adjacent paper, attached to the wooden pole mounted to the stand. The distance between these marks indicates the differences between soil type's densities.
This particular instrument was abandoned in a polytunnel at Newton and rescued along with the attached photographs and notes. Hence the mouse chewing and soil stains! I returned it to the Northern Research Station stores in 2016, where it may still lie.
Technology has moved on and light, portable, digital resistance penetrometers are now readily available.
All of the recovered images and documents can be viewed in the attached pdf file.
Acknowledgement and details of "J. H. Thomson, Newton" and "G. Taylor, Sighthill" (Sighthill was Forest Research's H.Q. in Scotland, before moving to the Northern Research Station, Roslin) would be welcome. Thank you.