Penetrometer

General:

This simple tool determines the degree of soil compaction at depths of 0-52.5 cm (0-21 inch). The penetrometer consists of an interchangeable tapered cone, a rod with depth markings at 7.5 cm (2.9 inch) intervals, a pressure chamber with precision drilling and a 0-60 bar pressure gauge. The diameters of the bore/piston and the base of the cone are essentially the same. This means that the pressure that can be read on the gauge is the same as the pressure required to push the tip of the rod through the ground.

Note: For a correct reading, the soil should be moist.

Guidelines and interpretation:

Highly compacted soil contains no air. Aerobic microbes, which require oxygen, are unable to make nutrients available to plant roots under such conditions. Good soil air content is very important for good, healthy growth of grass and other plants.

If the penetrometer reads less than 200 psi/ 14 bar, plant roots will show a good growth pattern. If more than 300 psi/ 21 bar is needed to push the tip through the soil, most plants will have very poor growing conditions.

With the 0 - 60 bar gauge, you can check how highly compacted the soil is and then measure the improvements created by adjustments in the tillage and aeration methods used. This allows you to make changes in tillage techniques and timing to see if there is a relative improvement. You can also evaluate the effectiveness of soil wetting agents.

Using the depth markings on the rod, you can determine the penetration resistance at different depths. By looking at the meter at the various markings, you can read the relative density at different depths.

Definitions:

Compaction (densification) is the degree of resistance to further penetration of soil by a point of a given shape and base surface, in units of pressure.

PRESSURE is the force per surface area, expressed in Kg/square cm² = Bar or pound per inch²= PSI (see scale penetrometer).

The projected surface area of the cone is 0.785 cm² or 0.122 inch²