Fall weather is generally full of ups and downs. As the weather turns cooler and the wind picks up, many of you are rushing to complete last-minute soil sampling before the ground freezes. Cold and wet weather can complicate the sampling process, and can cause great frustration when samples begin to stick in the probe. However, using a lubricant can help to reduce the sticking of samples in the probe and make the process work a bit easier on the sampler.
A number of different lubricants have been evaluated over the years for their effectiveness as a sampling aid and their impact on the analysis results. Two of the most commonly recommended lubricants are either WD-40, or aerosol cooking sprays such as Pam. Either of these products act as a water dispersant, effectively creating a film on the metal that repels water and limits the sticking within the tube. From anecdotal evidence, WD-40 tends to be a bit more persistent on the probe than does cooking spray, and therefore tends to require less frequent application.
The effect of either material generally has a negligible effect on measured levels of macronutrients. There is some evidence that suggests micronutrient levels may be affected somewhat, but the effect is generally pretty minor. WD-40 tends to affect micronutrient levels less than cooking spray, so it is recommended when micronutrients are to be analyzed. This may be more significant in soils that are naturally low in micronutrients because the slight variation in levels will be a larger percentage of the total levels. However, if the use of lubricants results in better quality sample collection, the benefits of using a lubricant should greatly outweigh any potential for contamination from the lubricant itself.