Calibrating the Troxler Soil Moisture Density Gauge

Dan Bloomer (LandWISE) and Bruce Searle (Plant & Food Research)

Soil Moisture-Density Gauges are commonly used in construction and roading to monitor soil density. This enables engineers to determine that sufficient compaction has been achieved to ensure foundation stability. This article summarises results from a Sustainable Farming Fund project co-funded by the Foundation for Arable Research and LandWISE. LandWISE cropping trials have often found yield limitations where legacy compaction is not removed prior to establishing a new crop. A study was undertaken to see if a soil moisture – density gauge can give a valid measure of soil density in cropping fields, whether soil density is altered by cultivation practices and if it affects yield.


Fig.1 Top view of Troxler Moisture-Density Meter

A Troxler 3440 soil moisture density gauge was used to assess soil at sites in Gisborne, Manawatu and Hawke’s Bay. One key advantage of the gauge is that measurements are completed quickly (a couple of minutes) in the field. Conventional sampling requires large samples to be taken, dried for several days in a lab, and then weighed to determine density and moisture.

Results showed the Troxler can give valid measures of soil density but must be calibrated for each soil type and depth. Some physical cores must be taken and processed to allow this. The calibration curves for two Hawke’s Bay soils are shown in Figure 2. These show the relationship between gauge soil density ‘estimates’ and soil density measured by removing, drying and weighing soil cores.



Figure 2. Relationship between estimated soil density obtained using individually calibrated Troxler measurements and soil core measured density for Twyford and Mangateretere soils.

Once calibrated, the Troxler offers the advantage of quickly collecting a large number of soil compaction measurements at different depths, without the cost of laborious soil sampling.  A draft protocol was prepared for calibration purposes. Project details here>

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